Unit 1 - Chemistry - Chapter 2 PDF

2 C H A P T E R Names, Formulas, How can you name and write formulas for ionic and molecular compounds to reflect their composition? How do theories of bonding in ionic and molecular compounds help explain their physical properties? What ar...

2 C H A P T E R Names, Formulas, How can you name and write formulas for ionic and molecular compounds to reflect their composition? How do theories of bonding in ionic and molecular compounds help explain their physical properties? What are some properties of acids and bases and what precautions should you take to work safely with them? 40 MHR Unit 1 Energy and Matter in Chemical Change and Properties T his spectacular limestone cave resulted from the interactions Some of the carbonic acid decomposes into carbon dioxide and water. As the of an ionic compound, a molecular carbon dioxide escapes into the air, the compound, and an acid. calcium carbonate stays on the cave The first stage in “cave building” ceiling and eventually forms stalactites. is the formation of layers of limestone. In this chapter, you will learn Over a period of millions of years, how to name and write formulas the shells of dead sea creatures form for ionic compounds such as calcium a calcium carbonate (CaCO3(s)), or carbonate, CaCO3(s), and for limestone, sea bed. Movements deep molecular compounds such as inside Earth lift the limestone layer carbon dioxide, CO2(g). You will above sea level. Eventually the original investigate and explain their properties sea bed becomes a limestone layer using bonding theories you learned deep below the surface of the land. in Chapter 1. You will also learn about Later, as rain falls through the the names, formulas, and properties atmosphere, carbon dioxide, CO2(g), of acids such as carbonic acid, in the air dissolves in the rainwater, H2CO3(aq), and bases. Finally, you forming carbonic acid, H2CO3(aq). will learn why the unique properties The acid seeps through the soil of water, the most familiar and plen- down to the limestone. tiful o o k i substance on Earth, are essential n L g Very slowly, the acid dissolves to life on this planet. head A the calcium carbonate and washes it away. Underground streams may o oki n In the Unit 1 Design L g speed the process. When large caverns Your Own Investigati on: head Analyzing Antacids A have formed, a reversal of the carving , you will need to ma use of some of the ke properties of acids process may occur. Small drops bases. As you work and through this chapter attention to the inf , pay close of calcium carbonate dissolved in ormation on acids and bases. Write down any qu estions that occur carbonic acid cling to the cave ceiling. you consider how to you as you will use your kn to design your expe owledge riment. Chapter 2 Names, Solar Formulas, Energy andand Properties Climates MHR 41  2.1 Chemical Names and Formulas Do you enjoy a sip of refreshing dihydrogen monoxide on a hot day? Do you like sodium chloride on your French fries? Do you take sucrose in your tea? You probably know these substances better as water, salt, and sugar — their common names. Figure 2.1 shows some other examples of chemicals with common names. Common names often tell very little about a substance. In the past, names often referred to the source, uses, or properties of a substance. Saltpetre, for example, is a salty-tasting chemical found crusted on rocks (petra in Greek). No one could guess from this name that saltpetre is a potassium compound. Chemists need a naming system that lets them identify the substance clearly. A chemical name also should describe the composition of a substance. As well, it should enable chemists to communicate results with other chemists around the world. A Sodium hydrogen carbonate, NaHCO3, is commonly called baking soda. It is often placed in refrigerators to prevent odours. The baking soda absorbs moisture and molecules that cause odour from the air. A B B Solid carbon dioxide, CO2, is often called dry ice because it resembles solid water (ice). Unlike ice, it does not melt under normal conditions. Instead, dry ice sublimes to form gaseous C carbon dioxide. C Limestone, used for building, is composed mainly of calcium Figure 2.1 Each of these compounds has a common name, a carbonate, CaCO3. Calcium carbonate also has the common systematic name, and a chemical formula. Which do you think is names chalk or calcite. most useful in identifying the compound? 42 MHR Unit 1 Energy and Matter in Chemical Change  The international system for naming chemicals is maintained by the International Union of Pure and Applied Chemistry www.mcgrawhill.ca/links/ (IUPAC). Founded in 1919, IUPAC has developed a systematic sciencefocus10 method to name chemicals according to their composition. Use Internet search tools to find the systematic Today, chemists all over the world use the IUPAC system. names and some uses for these common chemicals: This system ensures that each pure substance has a single, laughing gas, muriatic acid, milk of magnesia, lye, and lime. What are the origins of these common names? The unique name, called its systematic name. The name of a “official” rules for chemical nomenclature are summarized substance describes its composition. It also enables you to in the IUPAC “colour” books. (For example, the Green write its chemical formula and predict some of its properties. Book contains rules for quantities, symbols, and units For example, the systematic name for saltpetre is potassium of measurement.) You can investigate these books, and find out more about the history and role nitrate (KNO3). This name identifies the substance as an ionic of IUPAC, from its web site. Go to the web compound that contains potassium and nitrate ions. From this site above, and click on Web Links to information, a modern chemist can predict that, like all potassium find out where to go next. salts, potassium nitrate will dissolve readily in water. In this section, you will learn how to name several types of compounds from their formulas. You will also learn how to write a chemical formula when you are given the name of a compound. Later, you will study properties of different types of compounds. Binary Compounds Compounds that are made up of two elements are called binary compounds. Before chemical names were Sodium chloride, NaCl, is a binary compound. The same is true of nitrogen standardized, a single compound dioxide, NO2. Compounds that contain atoms of more than two elements might have more than one name. For example, sulfur dioxide (SO2) are not binary compounds. For example, sodium nitrate, NaNO3, is not a binary was known as both vitriolic acid compound. One way to identify a binary compound is to examine the ending air and sulfurous gas. of its name. The names of binary compounds that you will see in this textbook almost always end with the suffix “-ide.” Binary Molecular Compounds Table 2.1 Prefixes for Binary The prefix “mono” is A binary molecular compound forms when Molecular Compounds only used for the second atoms of two different elements group together element. When the second Prefix Number it as molecules by forming covalent bonds. Usually element is oxygen, the the two elements are non-metallic elements. These “o” is dropped. Thus the ➤ mono- represents 1 second part of the name is three rules will help you write the names and monoxide, not monooxide. di- 2 formulas of binary molecular compounds. tri- 3 1. The first element in the name and formula is usually the one that is tetra- 4 farther to the left on the periodic table. For example, in a compound penta- 5 containing carbon and oxygen, the carbon is named first because carbon is to the left of oxygen on the periodic table. hexa- 6 2. The suffix “-ide” is attached to the name of the second element. For hepta- 7 example, in a compound containing carbon and oxygen, the name octa- 8 “oxygen” is changed to “oxide.” nona- 9 3. Prefixes are used to indicate how many atoms of each type are present (ennea-) in one molecule of the compound. Table 2.1 lists the first ten prefixes. deca- 10 For example, a compound consisting of molecules with one carbon atom and two oxygen atoms is called carbon dioxide. Chapter 2 Names, Formulas, and Properties MHR 43  Study Table 2.2 to understand how to apply these rules. Table 2.2 lists different binary molecular compounds formed from nitrogen and oxygen. Table 2.2 Naming the Oxides of Nitrogen Formula Systematic name Common name Comments NO nitrogen monoxide nitric oxide helps to maintain blood pressure pollutant from vehicle exhaust N2O dinitrogen monoxide nitrous oxide also known as laughing gas NO2 nitrogen dioxide none brown gas used to manufacture nitric acid N2O3 dinitrogen trioxide none deep blue liquid N2O4 dinitrogen tetraoxide none used in rocket fuels N2O5 dinitrogen pentaoxide none dissolves in water to form nitric acid Figure 2.2 Car exhaust is a mixture of gases that includes carbon monoxide and carbon Practice Problems dioxide. For carbon monoxide, CO, carbon is to the left of oxygen 1. Write the name of each of the following molecular compounds: in the periodic table, so it comes (a) SO2 (b) SO3 (c) OF2 (d) O2F2 first in both the name and formula. The “di-” prefix of carbon dioxide, 2. Write the formula for each of the following molecular compounds: CO2, you now know. (a) sulfur difluoride (c) sulfur hexafluoride (b) sulfur tetrafluoride (d) disulfur difluoride 3. Write the name for each of the following molecular compounds: (a) CCl4 (b) SF2 (c) CO (d) PCl5 4. Write the formula for each of the following molecular compounds: (a) dinitrogen oxide (c) disulfur trioxide (b) carbon dioxide (d) carbon tetrafluoride Names and Formulas for Binary Ionic Compounds A binary ionic compound is composed of ions of one metal element and ions of one non-metal element joined by ionic bonds. The name of a binary ionic compound is formed from the names of its elements. These three rules can help you Look back to Figure 1.28 on page write the names and formulas of binary ionic compounds. 31. The figure shows the crystal lattice for sodium chloride, NaCl. 1. The first element in the name and formula is the metal. Copy the figure into your note- 2. The second element, the non-metal, is named as an ion. In other words, book. Circle a portion of the crystal lattice that represents one the suffix “-ide” is attached to the name. For example, the compound formula unit of sodium chloride. formed from lithium and fluorine is named lithium fluoride. 3. The chemical formula shows the simplest whole number ratio of each type of ion in the compound. For example, the formula CaF2 indicates that any crystal of calcium fluoride contains two fluoride ions for every calcium ion. Note that because ionic compounds are crystal lattices, their formulas do not represent molecules. Instead, the formulas represent the smallest repeating unit within the lattice. These repeating units are called formula units. 44 MHR Unit 1 Energy and Matter in Chemical Change  The names of ionic compounds do not contain prefixes. Therefore, to determine the formula for the compound, you must deduce the number of each type of ion in a formula unit of the substance. You can do this by thinking of the number of electrons transferred when the compound forms. You find the number of transferred electrons using the ion charges given on the periodic table. Remember that an ionic compound is electrically neutral. (Its overall charge is zero.) So, in one formula unit of an ionic compound, the total positive charge on the cations plus the total negative charge on the anions is equal to zero. Model Problem 1 Predict the formula of calcium fluoride. The small lowered numbers in chemical formulas are called Solution subscripts. They indicate the number of particles of a particular Identify the type of compound. Since the compound contains a metal element found in the smallest and a non-metal, it is ionic. possible unit of a compound. Use ion charges from the periodic table or your knowledge of the The prefix “sub-,” meaning “below,” describes the position groups to determine the charges on the ions. In an ionic compound, of the number. How many other calcium tends to form a calcium cation with a charge of 2! (Ca2!). “sub-” words do you know? In an ionic compound, fluorine tends to form a fluoride anion with a charge of 1" (F"). The compound must be electrically neutral. Therefore, one formula unit of the ionic compound must contain two fluoride ions, each with a charge of 1", and one calcium ion with a charge of 2!. The formula for the compound is CaF2. Check your answer by adding the total charges on the ions: !2 ! [2 # ("1)] $ 0 The total charge adds up to zero. The formula is correct. You can figure out the formula for calcium fluoride by picturing an electron transfer, as shown in Figure 2.3. Practice Problems Ca F 5. Write the name of each of the following ionic compounds: (a) LiCl (b) KBr (c) CaCl2 (d) MgO F 2+ – 6. Predict the formula for each of the following ionic compounds: [Ca] [ F ] (a) sodium fluoride (c) barium bromide – (b) magnesium fluoride (d) aluminium chloride [F] 7. Write the name of each of the following ionic compounds: Figure 2.3 In one formula unit (a) KF (b) K2O (c) CaO (d) BeF2 of calcium fluoride, one calcium atom gives up two of its electrons, 8. Predict the formula for each of the following ionic compounds: and two fluoride atoms each accept one electron. (a) lithium bromide (c) potassium nitride (b) magnesium sulfide (d) aluminium oxide Chapter 2 Names, Formulas, and Properties MHR 45  Cation Charges Atoms of some elements can form more than one ion. For example, most of the transition metals (the elements in groups 3 to 12 on the periodic table) are able to form more than one cation. The periodic table in Appendix B shows some common ions of the transition metals. For example, nickel can form the cations Ni2! and Ni3!. Copper can form the cations Cu! and Cu2!. If you are given the formula of an ionic compound, you can determine the charge on the cation. Model Problem 2 Which copper cation, Cu! or Cu2!, is in CuCl2? Solution Begin by writing the two ions involved. You know that a chloride anion has a charge of 1". You are not sure of the charge on the copper ion — it could be either 1! or 2!, according to the periodic table. Cu? Cl" The compound must be electrically neutral. There are two chloride ions in CuCl2. Therefore, the single copper ion must have a charge of 2! to balance the two chloride ions. The copper cation is Cu2!. Check your answer by adding the total charges on the ions: !2 ! [2 # ("1)] $ 0 The total charges add up to zero. The answer is correct. Practice Problems 9. Determine which iron cation, Fe2! or Fe3!, is in each of the following binary ionic compounds: (a) FeCl2 (b) FeO (c) Fe2O3 (d) FeBr3 10. Determine the charge of the cation in each of the following binary ionic compounds: (a) SnBr4 (b) FeN (c) PbO (d) PbO2 Naming Cations Using the Stock System The current way to distinguish between cations was invented by a German chemist, Alfred Stock. In the Stock system, the charge on the cation is written, in parentheses, as a Roman numeral after the name of the metal. (The first ten Roman numerals are I, II, III, IV, V, VI, VII, VIII, IX, and X.) For example, Cu! is called copper(I). Cu2! is called copper(II). The Stock system is used only for metals that have more than one type of cation. You do not need to write sodium(I), because sodium forms only one type of cation: Na!. When an ionic compound is named using the Stock system, the name tells you the cation charge to use. 46 MHR Unit 1 Energy and Matter in Chemical Change  Model Problem 3 Write the chemical formula for copper(II) oxide. You may need to write the formula Solution for an ionic compound without Because the copper cation is named copper(II), it must be Cu2!. knowing the Stock name. In that case, choose the most common According to the periodic table, the oxide anion is O2". cation, as indicated on the periodic The compound must be electrically neutral. Therefore, one formula table in Appendix B. For example, suppose you were asked to write unit must contain one copper(II) cation and one oxide anion. the formula for an ionic compound The formula for the compound is CuO. containing mercury and iodine. The best answer is HgI2, because Hg2! Check your answer by adding the total charges on the ions: is a more common ion than Hg!. !2 ! ("2) $ 0 Now write the formula for an ionic compound containing lead The total charge adds up to zero. The formula is correct. and bromine. Practice Problems 11. Write the formula for each of the following ionic compounds. (a) colbalt(II) chloride (c) molybdenum(VI) chloride (b) chromium(III) oxide (d) lead(IV) oxide 12. Determine which cation is in each of the following compounds. Then, write the name of the compound using the Stock system. (a) SnO2 (c) TiCl4 (b) CuBr (d) PdO In Investigation 2-A, you will practise using the rules for writing names and formulas of binary ionic compounds. The classical system for naming transition metal cations is based on the Latin names for metals. For example, the Latin names for iron, copper, and lead are ferrum, cuprum, and plumbum. To indicate the ion with the higher charge, the “um” ending is dropped, and the suffix “-ic” is added. The suffix “-ous” indicates the ion with the lower charge. Copy and complete the table below by adding the missing names. The first line is given to help you. Element Latin name Ion with Ion with lower charge higher charge The classical system for naming compounds is still iron ferrum ferrous Fe2! ferric Fe3! used. Compare the Stock cuprum Cu! Cu2! system with the classical system. Which do you think plumbum Pb2! Pb4! works better, and why? Chapter 2 Names, Formulas, and Properties MHR 47  S K I L L C H E C K Initiating and Planning Performing and Recording 2-A Analyzing and Interpreting Communication and Teamwork Writing Names and Formulas of Binary Ionic Compounds Think About It Examine the type of elements in each of 3 Ionic bonding involves the transfer of electrons to the following substances. Identify whether form ions with the same electron configuration as each name or formula represents an ionic a noble gas. In this investigation, you will use the or molecular substance. periodic table to predict the number of electrons (a) sodium sulfide transferred in the formation of some binary ionic (b) PCl3 compounds. Then, you will use this information to (c) nitrogen dioxide determine the chemical formula of each substance. (d) zinc oxide Apparatus (e) MgI2 periodic table notebook 4 Remember that the name of a binary ionic compound begins with the name of its cation (metallic) and ends with the name of its anion What to Do (non-metallic). The anion name ends with “-ide.” 1 Review the definition of a binary compound on Copy the table below and use this information page 43. Then, identify the binary compounds in to complete it. the following list: (a) HCl Element Anion (b) SO3 Name Symbol Name Symbol (c) MgCO3 fluorine F fluoride F– (d) hydrogen sulfide chloride (e) sodium hydrogencarbonate bromide As you have seen, the naming system for ionic oxide 2 substances differs from the naming system for sulfide molecular substances. nitride (a) Which types of elements combine to form binary ionic compounds? 5 Copy the formulas below. Find the total charge (b) Which types of elements combine to form on the cations and the total charge on the anions. molecular compounds? Classify each formula as correct or incorrect. Correct the incorrect formulas. Finally, write the name of each compound. (a) LiO (b) MgO (c) K2S (d) AlBr3 (e) NaN3 48 MHR Unit 1 Energy and Matter in Chemical Change 6 Work through the following examples. Then 8 Many transition metals form more than one answer question 7 to practise writing formulas. cation. You can use the formula of an ionic compound to determine the charge on the cation. A Determining the formula of magnesium chloride Copy the following example, and explain it to a Based on your understanding of valence partner so that you will remember how it works. electrons and the periodic table, you know that in an ionic compound, magnesium forms A Formula: FeCl3 a cation with a charge of 2+, and chlorine forms an anion with a charge of 1–. One formula unit of FeCl3 contains three chloride anions and one iron The compound must be electrically cation. Each chloride ion has a neutral. Therefore, one formula unit charge of 1–. The total charge of must contain two chloride ions and the anions is therefore 3–. Iron one magnesium ion. cations have a charge of either 2+ or 3+, according to the periodic magnesium chloride table in Appendix B. Check your answer by adding the total charges on Since the compound must be electrically neutral, the ions: +2 + [2 x (–1)] = 0 the iron ion must have a charge of 3+ to balance the The total charge is zero. The answer is correct. total charge of the anions. In FeCl3, the iron cation is B Determining the formula of calcium oxide Fe3+. In an ionic compound, calcium forms a cation B Formula: FeO with a charge of 2+, and oxygen forms an anion with a charge of 2–. One formula unit of FeO contains one oxide anion and one iron The compound must be electrically cation. Each oxide anion has a neutral. Therefore, one formula unit charge of 2–. must contain one calcium ion and one oxide ion. Since the compound must be electrically neutral, the iron ion must have a charge of 2+. In FeO, the iron calcium oxide cation is Fe2+. Check your answer by adding the total charges on the ions: +2 + (–2) = 0 The total charge is zero. The answer is correct. 9 Find the charge on the cation in these compounds. Decide if your answers are reasonable before you move on to step 10. 7 Write the formula of each of the following (a) Cu2S compounds: (b) Cr2O3 (a) beryllium fluoride (c) PbO2 (b) sodium nitride (d) NiCl2 (c) calcium sulfide (e) CrN (d) aluminium chloride (f) HgO (e) lithium oxide (f) magnesium nitride (g) gallium sulfide (h) barium bromide CONTINUED Chapter 2 Names, Formulas, and Properties MHR 49 0 Copy and complete the following table by adding @ Write the chemical formula for each of the the missing Stock system names. The first line is following compounds. given to help you. (a) copper(I) oxide Stock System Naming (b) lead(IV) bromide Formula Ion Name (c) iron(III) sulfide FeCl3 Fe3! iron(III) chloride (d) nickel(III) fluoride (e) manganese(IV) sulfide FeO Fe2! Cu2S Cu! # What happens when you do not have the Stock name of an ionic substance to help you write its PbO2 Pb4! formula? In that case, choose the most common cation of the transition metal, as indicated on the When the Stock system is used to name an ionic periodic table in Appendix B. Write formulas to ! represent the following compounds, choosing compound, you can tell immedicately which cation charge to use. Copy the following example, the most common cation. then move on to question 12. (a) an ionic compound containing iron and chlorine Writing a chemical formula given the Stock system name (b) an ionic compound containing titanium of a compound and fluorine 2+ In iron(II) sulfide, the iron cation must be Fe. (c) an ionic compound containing platinum 2– According to the periodic table, the sulfur anion is S. and oxygen For the compound to be electrically (d) an ionic compound containing lead neutral, there must be one iron ion and oxygen for each sulfur ion. iron(II) sulfide Analyze Check your answer by adding the total charges on the ions. +2 + (–2) = 0 1. Explain why you must use the Stock system to The total charge is zero. The answer is correct. name ionic compounds containing transition metals. In which cases do you not need to use the Stock system to name an ionic compound? Explain your answer. 2. There is something wrong with the name written beside each of the following compounds. In each case, explain why the name is wrong, and then write the correct name. (a) Ti2O3, dititanium trioxide (b) NaCl, sodium(I) chloride (c) CuCl2, copper chloride (d) NO2, nitrogen(IV) oxide 50 MHR Unit 1 Energy and Matter in Chemical Change Compounds Containing Polyatomic Ions Many ionic compounds are not binary because one or both ions contain atoms Table 2.3 Common Polyatomic Ions of more than one element. These polyatomic ions consist of one or more Name Chemical different atoms, which are joined by covalent bonds. As a group, these bonded formula atoms have an overall positive or negative charge. An example of a polyatomic ammonium NH4! ion is the nitrate ion, NO3". In the nitrate polyatomic ion, one nitrogen atom hydroxide OH" and three oxygen atoms are joined by covalent bonds. As a unit, they have a net carbonate CO32" charge of 1". Many common polyatomic ions are negatively charged and have names ending in “ate.” You will find it helpful to memorize the names, formulas, nitrate NO3" and charges of the ions shown in Table 2.3. You will find the names, formulas, sulfate SO42" and charges of more polyatomic ions on the periodic table in Appendix B. hydrogencarbonate HCO3" Compounds containing polyatomic ions are classified as ionic. To name these hydrogensulfate HSO4" compounds, use the name of the cation, followed by the name of the anion. For example, NH4NO3 is named ammonium nitrate. When writing formulas, you phosphate PO43" must use parentheses around the polyatomic ion when more than one is present in a formula unit. For example, aluminium nitrate must contain three nitrate ions, NO3", for every aluminium ion, Al3!. This combination gives a net charge of zero. To show this clearly, the formula is written Al(NO3)3. Model Problems 4 and 5 below give more examples of writing names and formulas for compounds that contain polyatomic ions. Model Problem 4 What is the formula of ammonium sulfide? Solution Compounds with polyatomic The compound contains a polyatomic ion, so it is ionic. Name it ions contain both ionic and without using prefixes. Write the formula of each ion: covalent bonds. For example, sodium sulfate, Na2SO4, is classified as an ionic substance because it is Since the compound must be electrically neutral, there must be two made up of different ions. ammonium ions for every sulfide ion. Sodium sulfate dissolves in water, and the solution Use parentheses to indicate the two ammonium ions present. conducts electricity. Because The formula of ammonium sulfide is (NH4)2S the sulfate ion, SO42", is made up of non-metal atoms, Check your answer by adding the total charges on the ions. however, the bonding [2 # (!1)] ! ("2) $ 0 between the sulfur and oxygen atoms is covalent. The total charge is zero. The answer is correct. Model Problem 5 What is the name of CuCO3? Solution From the periodic table in Appendix B, the two possible ions of copper are Cu! and Cu2!. From Table 2.3 above, the carbonate ion has a charge of 2". There is one copper ion and one carbonate ion in each formula unit of CuCO3. Since the compound must be electrically neutral, the copper ion must be Cu2!. The name of CuCO3 is copper(II) carbonate. Chapter 2 Names, Formulas, and Properties MHR 51  Practice Problems 13. Write the name of each of the following compounds: (a) NaNO3 (c) CuHCO3 (b) CaSO4 (d) Cu(OH)2 14. Predict the formula of each of the following compounds: (a) magnesium sulfate (c) ammonium hydroxide (b) sodium phosphate (d) copper(II) nitrate 15. Write the name of each of the following compounds. To find the name of some of the polyatomic ions, you will need to refer to the periodic table in Appendix B. (a) Sr(ClO2)2 (d) Na2Cr2O7 (b) Ba(CH3COO)2 (e) KSCN (c) Ca(IO3)2 (f ) FeSO4 16. Write the formula of each of the following compounds. To find the formula and charge of some of the polyatomic ions, you will need to refer to the periodic table in Appendix B. (a) ammonium chloride (d) calcium sulfite (b) sodium hydrogensulfite (e) nickel(II) phosphate (c) potassium dihydrogenphosphate Families of Polyatomic Anions You may have noticed that many polyatomic anions are composed of oxygen and one other non-metallic element. Nitrate, NO3", and sulfate, SO42", are two common examples. Nitrite, NO2", and sulfite, SO32", are two other examples. What do you notice about the names, formulas, and charges of the nitrate and nitrite anions? What do you notice about sulfate and sulfite? Anions that contain oxygen, such as sulfate and sulfite, or nitrate and nitrite, are part of the same families of polyatomic anions. They contain the same elements and have the same charge. Their names and formulas are slightly different, however. You can use a series of rules to name anions that belong to these families. The rules are outlined below. In each family, the anion with the ending “-ate” serves as a reference point. In the example in Table 2.4, nitrate, NO3", is the reference. The other anions Table 2.4 A Family of are named according to the number of oxygen atoms in their formula, in Oxygen-Containing Anions relation to the reference anion. Anion name Formula Compared with an “ ate” anion, an anion named “ ite” has one less pernitrate NO4" oxygen atom in its formula. Compare nitrate, NO3 , with nitrite, NO2". " nitrate NO3! Anions that have two less oxygen atoms than the reference anion are named nitrite NO2" “hypo ite”, as in hyponitrite, NO". Anions that have one more oxygen atom than the reference anion are called hyponitrite NO" “per ate”, as in pernitrate, NO4". 52 MHR Unit 1 Energy and Matter in Chemical Change Answer the following questions. They will help you practise naming oxygen- containing anions based on the rules you have just learned. Practice Problems 17. The anion sulfate has the formula SO42". What is the formula and charge of the sulfite anion? 18. The anion chlorate has the formula ClO3". What is the formula and charge of the hypochlorite anion? 19. The anion iodate has the formula IO3". What is the formula and charge of the periodiate anion? Find Out The Ionic Card Game How well do you understand the rules for classify- 2. Prepare cards and a detailed set of rules for ing and naming ionic compounds? In the following your game. activity, apply your knowledge to design a chemical card game. 3. Try several rounds of your game within your group. Refine the rules as necessary. Materials 4. Exchange games with at least one other group. pencils After playing each game, complete an evalua- felt markers tion of the game as directed by your teacher. index cards What Did You Find Out? Analyzing and Interpreting Initiating and Planning Procedure Communication and Teamwork 1. What were the main difficulties your group 1. Work with your group to design a card game faced in designing and producing the game? that involves naming and finding formulas for 2. How did your game differ from those of ionic compounds. Consider the following other groups? points as you design your game. Your game must include a variety of ions, 3. What would you improve about your game including polyatomic ions, and must if you were to redesign it? Give reasons for involve combining them to make formula each change. units with a net charge of zero. 4. How has producing and playing a card game The game must include at least 32 cards. helped you learn and practise naming rules You may base the game on other card and formula-writing rules for ionic compounds? games, or you may invent a new game entirely. The game should involve two to four players and require no more than 15 min to complete. Chapter 2 Names, Formulas, and Properties MHR 53  Hydrogen Compounds www.mcgrawhill.ca/links/ One important group of compounds seems to break the sciencefocus10 naming rules given in this section. You might think that How many chemicals are there? Scientists are still HCl, for example, would be ionic. It contains hydrogen counting. The Chemical Abstracts Service (CAS) of (found with the metals on the periodic table) and a non- the American Chemical Society maintains a very large database of substances. In mid-August, 2002, the CAS metal. In fact, hydrogen is a non-metal, and HCl is known Registry was adding about 4000 new substances per to be molecular. It is the same for most other compounds day and contained a total of 20 124 413 different whose names begin with “hydrogen”. The names of these compounds. You can check the CAS Substance molecular substances, however, do not use prefixes. The Counter on the Internet to find the current number. Go to the web site above, and correct name for the molecular compound HCl is hydrogen click on Web Links to find out chloride, not hydrogen monochloride. Similarly, H2S is hydrogen where to go next. sulfide, not dihydrogen monosulfide. You will learn more about this type of substance in section 2.3. Compounds containing hydrogen and carbon, such as ethane, C2H6, or ethanol, C2H5OH, have another set of naming rules, which you will learn in later science courses. Table 2.5 shows some examples of important compounds that contain hydro- gen. You should memorize the names and formulas of these common compounds. Table 2.5 Selected Hydrogen-Containing Compounds Formula Name Comments H2O water known as ice in its solid form and water vapour in its gaseous form NH3 ammonia a gas used in household cleaners and fertilizers CH4 methane natural gas is composed mostly of methane colourless and odourless CH3OH methanol a liquid also known by its common name, wood alcohol used as a disinfectant, in antifreeze, and as a paint thinner Section 2.1 Summary In this section, you learned how to name and write formulas for ionic and molecular compounds. Table 2.6 below summarizes some of the key points Table 2.6 A Summary to remember when naming molecular compounds and ionic compounds. of Key Naming Rules Molecular Compounds Ionic Compounds Binary molecular compounds Binary ionic compounds These compounds contain two non-metal elements. These compounds contain one metallic element and one non-metallic element. The leftmost element on the periodic table is written first in the name and the formula. The metallic element (the cation) is named first. These compounds are named using prefixes to indicate the number The name of the non-metallic element (the anion) is changed of atoms in each molecule (e.g., P2O5, diphosphorus pentoxide). to “-ide” (e.g., sodium chloride). The prefix “mono-” is omitted in the first element named Cations with more than one possible charge are named using (e.g., CO2, carbon dioxide). the Stock system. Subscripts in the formulas of these compounds indicate the The total charge of anions and cations must equal zero. number of atoms in each molecule (e.g., a molecule of CO2 Ionic compounds with polyatomic ions contains one carbon atom and two oxygen atoms). Refer to the periodic table for names and charges of polyatomic ions. Treat a polyatomic ion as a unit. 54 MHR Unit 1 Energy and Matter in Chemical Change Check Your Understanding 1. Name each of the following ionic compounds: (a) MgBr2 (b) KHSO4 (c) (NH4)3PO4 (d) Ca(OH)2 2. Name each of the following molecular compounds: (a) CF4 (d) PCl3 (b) PH3 (e) N2F4 (c) P4O10 (f) O2F2 3. Copy the following list of compounds in your notebook. Identify each compound as ionic or molecular. Mark the binary compounds with an asterisk (*). Name each compound using the appropriate method. (a) P2O5 (b) CaSO4 (c) KNO3 (d) MgI2 4. Write the formula for each of the following compounds: (a) phosphorus pentachloride (b) sulfur hexafluoride (c) nitrogen trifluoride (d) silicon tetrafluoride (e) silver phosphate (f) manganese(II) dichromate (g) sodium perchlorate (h) cobalt(II) permanganate 5. Write the systematic name for each of the following substances: (a) water, H2O (b) ammonia, NH3 (c) potash, K2CO3 (d) lye, NaOH 6. Thinking Critically Explain why a standard naming system is important for international communication, safety, and efficiency. Chapter 2 Names, Formulas, and Properties MHR 55  2.2 Explaining Properties of Substances Table 2.7 Abbreviations for States One mark of a valid theory is its State Abbreviation Examples (at room temperature) ability to explain observations. In solid (s) iron: Fe(s) this section, you will investigate the sodium chloride: NaCl(s) properties of ionic compounds and liquid (!) water: H2O(!) molecular compounds. You will use octane (found in gasoline): C8H18(!) the theory you learned in section 1.3 gas (g) helium: He(g) to explain what you observe. Then, nitrogen: N2(g) you will investigate the properties aqueous (aq) sodium chloride solution (brine): NaCl(aq) of two other important classes (dissolved in water) ammonia solution (found in glass cleaner): NH3(aq) of substances. Bonding and Properties Chemists can infer many features of the structure and bonding of different substances. They do this by observing their physical and chemical properties. For example, physical properties such as structure, melting and boiling points, and electrical conductivity give important clues about bonding in ionic compounds and molecular compounds. It is important to know the state of a substance because substances have different properties in different states. For example, substances have different properties when they are dissolved in water. To avoid confusion, chemists use subscripts to show the state of a substance when writing its formula. Table 2.7 shows these subscripts. Properties of Ionic Compounds You can see some important properties of sodium chloride, NaCl(s), in Figure 2.4. Note that a red light indicates when a substance is conducting electricity. In the solid state, ionic compounds have regular crystalline shapes with flat sides. This property suggests that the ions in the crystal are arranged in a regular, repeating pattern. As you know, scientists call this pattern a crystal lattice. A Figure 2.4 Like most ionic compounds, sodium chloride (A) has a relatively high melting point (801˚C). It conducts electricity in solution (B), and B C does not conduct electricity in its solid state (C). 56 MHR Unit 1 Energy and Matter in Chemical Change  Ionic compounds tend to have fairly high melting points. This property suggests that the attraction between positively and negatively charged ions in the lattice is strong and extends throughout the crystal. A great deal of energy is required to break the strong ionic bonds. In the solid state, ionic compounds do not conduct electricity. This property suggests that the ions in the lattice are not free to move. When melted or dissolved in water, ionic compounds are electrolytes. They conduct electricity. This property suggests that melting and dissolving break down the crystal lattice and allow ions to move freely and carry charge. Properties of Molecular Compounds Properties of molecular compounds can also be used to build up a picture of their structure. Figure 2.5 shows glucose solid and solution being tested for electrical conductivity. Most molecular compounds have fairly low melting points. This property suggests that the attractive forces between molecules must be weak and easy to overcome. Once melted, molecular compounds can usually be heated further without decomposing into other compounds or elements. This property suggests that the covalent bonds within molecules must be strong. Molecular substances tend to be non-electrolytes. They do not conduct electricity in any state as pure substances. This property suggests that molecular substances are not made of ions. They do not conduct electricity even in liquid form, because the liquid contains only neutral molecules. When dissolved in water, most molecular substances do not conduct electricity. However, some molecular substances do conduct electricity when dissolved in water. This observation suggests that some molecular substances can form ions when they are dissolved in water. When a substance that is dissolved in water conducts electricity, you cannot be sure whether it is an ionic compound or a molecular compound. You must perform further tests. Figure 2.5 Like most molecular compounds, glucose does not conduct electricity either in solid form (A) or in an aqueous solution (B). Glucose is a solid at room temperature, but it has a relatively low melting point (146°C). Many molecular compounds, such as sulfur dioxide, SO2(g), are gases at room temperature. Many others are liquids. In the investigation that follows, you will design a procedure to identify substances as ionic or molecular, based on their properties. You will explain why theories of ionic and covalent bonding help to describe the different properties of substances. Chapter 2 Names, Formulas, and Properties MHR 57  S K I L L C H E C K Initiating and Planning Performing and Recording 2-B Analyzing and Interpreting Communication and Teamwork Ionic or Molecular? Scientists often work in the same way as detectives. Like detectives searching for clues, chemists classify substances by matching observations against theories about ionic and molecular compounds. In this investigation, you will try to determine the type of bonding in several common substances by observing their properties. Question Which substances in this investigation are composed of molecules, and which are composed of ions? Prediction Read Procedure steps 1 to 6. Before you write your procedure, examine the substances you will be investigating. Describe their physical appearance. Predict whether your tests will determine whether each one is ionic or molecular. Safety Precautions Procedure 1 With your group, decide on a set of at least five observations, including a conductivity test, This may be the first time you work with chemicals which will help you determine whether each in this course. If so, review the general laboratory safety procedures outlined on page xiv of this substance is ionic or molecular. You may include textbook. Your teacher may provide additional tests using any of the apparatus listed. Qualitative guidelines specific to your school. observations are fine, too. For example, you can Review with your teacher the safety hazards of the describe the melting point as “low” or “high,” chemicals you will be using. Be sure you understand depending on whether the substance melts in the MSDS information for these chemicals, and use a beaker sitting on a hot plate at low heat. You recommended handling and disposal procedures. can also describe the odour of the substances. If you have medical conditions, such as allergies or asthma, inform your teacher and find out appropriate Write a step-by-step procedure for your tests. precautions to take before beginning the investigation. 2 CAUTION: If you are going to use smell as Be sure to wear gloves, safety glasses, and protective one of your tests, be sure to include the correct clothing while you are working in the lab. procedure for doing so. CAUTION: Never Apparatus Materials taste any substances in the laboratory. magnifying lens 9 labels 3 Design a data table to record your 5 beakers (100 mL) distilled water observations. Use a grid format, with scoopula solid honey (paraffin wax is an alternative) space for observations of each substance stirring rod in a separate row. conductivity tester Epsom salts hot plate lauric acid Have your procedure and data table approved 4 test tube rack washing soda by your teacher. 4 test tubes test tube holder 58 MHR Unit 1 Energy and Matter in Chemical Change  S K I L L C H E C K Initiating and Planning Performing and Recording xx-A Analyzing and Interpreting Communication and Teamwork 5 Perform each test and record your observations. If you decide to test the substance after it has been dissolved, be sure to include observations For tips on designing an investigation, of a control sample of distilled water. turn to Skill Focus 5. 6 When your tests are finished, dispose of each sample and clean your workspace and apparatus as directed by your teacher. Wash your hands thoroughly. Analyze 1. What do the relative melting points suggest 7. Share your results with others in your class. about the bonding within each substance? Discuss any classifications about which you disagree and suggest a method of resolving 2. Classify each substance as an electrolyte or the disagreement. a non-electrolyte. On which test do you base this classification? 8. Discuss how this investigation would change if you made quantitative, rather than qualitative, 3. What is the purpose of testing a control, as observations. Which of your observations or you did in Procedure step 5? Did all your tests could be made in a quantitative fashion? observations require a control? Explain Would your confidence in your classification why or why not. be improved by using quantitative observations? Would there be any disadvantages to making Conclude and Apply this investigation quantitative? 4. Which of the compounds in this investigation are made of ions? Which compounds are made Extend Your Knowledge of molecules? Explain why you classified each 9. Use Internet or print resources to investigate substance the way you did. the substances you tested in this investigation. 5. Which substances were the most difficult to If possible, write the IUPAC name and formula classify? Describe any inconsistencies in your for each substance. If it is not possible to name observations. For example, perhaps one test and write the formula of a substance, explain suggests that the substance is ionic even though why. Hint: At least one of the substances is not all the other tests suggest that it is molecular. a pure substance. 6. Choose one of your tests and evaluate it in detail. Identify the manipulated and responding variables. Which variables (if any) were controlled? Were the results clear and easy to interpret? Based on your experience, how could the testing procedure be improved or made more precise? Chapter 2 Names, Formulas, and Properties MHR 59  Assessing the Risk: Toxic Properties of Substances Nicotine-like chemicals are being Industrial workers who handle the molecular substance ethanol, C2H5OH(!), investigated for their potentially are warned that the chemical can be harmful. The MSDS for pure ethanol useful medicinal effects. They may be useful in the treatment of states that it can cause mutations, damage unborn children, irritate the skin Alzheimer’s disease, Parkinson’s and lungs, cause unconsciousness, and damage the liver and nervous system. disease, some mental illnesses, Despite these hazards, people expose themselves to ethanol solutions daily. and adult ADD. Some chemicals that are related to nicotine appear They do so every time they drink an alcoholic beverage. to improve memory and learning Life in our modern society can involve the use of many chemicals with in rats, and may protect rat brain properties that produce pronounced physical and psychological effects. Society’s cells from some toxins. Other attitude to these substances varies. Some of them are widely accepted. Caffeine, chemical relatives of nicotine are effective painkillers. Nicotine for example, is a powerful stimulant that is found in coffee, tea, cocoa, and itself is a “dirty drug,” whose chocolate (Figure 2.6). It is a diuretic, meaning that it causes more frequent negative effects often counteract urination. It also increases blood pressure by constricting blood vessels. Caffeine its possible benefits. Tobacco is not classified as a hazardous substance. Its use is not regulated. Controlling products, such as cigarettes, with their mix of potent chemicals, your caffeine intake is a personal decision. have no known medical use. On the other hand, governments and other bodies strictly regulate the use of some substances. Many performance-enhancing drugs, for example, are strictly banned from athletic competitions. The use and sale of many psychoactive drugs, such as cocaine, heroin, and ecstasy (MDMA), are illegal. People under a certain age cannot legally purchase alcoholic beverages and cigarettes. In the last decade, many towns and cities have decided to ban smoking in public places. Knowing about chemistry can help people make informed personal decisions about whether to include potentially harmful chemicals as part of their lifestyle. Table 2.8 outlines some information about the chemicals in alcoholic beverages and tobacco products and their effects. In the next investigation, you will have Figure 2.6 Caffeine is present in a chance to find similar information about another chemical that you wish varying amounts in all these items. to research. Table 2.8 Ethanol and Nicotine Products Alcoholic beverages Tobacco products Active ingredient ethanol, C2H5OH(!) nicotine, C10H14N2(!) Toxicity Drinking 50 mL of pure ethanol can lead to death. Absorbing one drop of nicotine through the tongue can cause death. (In tobacco plants, nicotine functions as a natural insecticide.) Physical effects increased risk of fetal alcohol syndrome in unborn increased heart rate and blood pressure child if alcohol consumed during pregnancy suppressed appetite temporary loss of coordination and slurred digestive problems and vomiting speech (“drunkenness”) reduced body temperature damage to brain, pancreas, liver, and kidneys increased risk of lung cancer and other lung problems increased risk of cancer of the stomach, mouth, and liver possible medicinal uses impotence and infertility Effect on depressant (reduces activity in brain areas that stimulant nervous system control behaviour) release of dopamine, a brain chemical associated temporary confusion and inability to think clearly with feelings of pleasure and relaxation increased risk of seizures Addictiveness Both physical and psychological dependence develop. Both physical and psychological dependence develop. Tolerance develops slowly, so larger doses are Tolerance develops rapidly, so larger doses are eventually needed to produce the same effect. quickly needed to produce the same effect. Associated Other chemicals in alcoholic beverages are not Other chemicals in tobacco smoke are even more toxic chemicals generally hazardous. than nicotine. 60 MHR Unit 1 Energy and Matter in Chemical Change  S K I L L C H E C K Initiating and Planning Performing and Recording 2-C Analyzing and Interpreting Communication and Teamwork Reducing the Risk Think About It Deciding to use chemicals always involves balancing 5 Creatively present your findings and action risks and benefits based on what you know about plan. For example, you may present your work their properties. In this investigation, you will create as a poster, a slide show, or a web page. an action plan for regulating the use of a particular chemical so that people can enjoy its benefits (if any) while minimizing its risk to human health and to the Analyze environment. Try to create an action plan that is 1. Compare the action plans proposed by the imaginative, feasible, and likely to be effective. different groups. Which action plans seemed What to Do most likely to be successful? 1 As a group, choose a widely used chemical to 2. Problems associated with a particular investigate. Some possibilities are listed below: chemical may take years to discover. The chlorine or fluoride chemicals added to anti-nausea drug thalidomide, for example, drinking water was introduced in the late 1950s. Not until formaldehyde-emitting glues used in 1961 did scientists realize that many women plywood and chipboard who took thalidomide during pregnancy gave a medicine birth to children with missing or deformed “road salt” used to melt ice limbs. How did each group’s action plan deal with the possibility that an apparently useful addictive chemicals discussed in this section chemical might have unsuspected long-term MSG (monosodium glutamate) or another side effects? food additive 3. The sale and use of alcoholic beverages 2 Gather information on the benefits of using was completely banned in Alberta during the chemical and the specific hazards it presents Prohibition (1916–1924). Despite harsh to human health and to the environment. Such penalties, however, many people disregarded risks may arise while in producing, distributing, the law. How did each group’s action plan using, recycling, or disposing of the chemical. Use Internet and print resources. The Merck encourage people to follow regulations and Index is a useful starting point for information guidelines for using the chemical? about chemicals and their properties. Extend Your Knowledge 3 Find out whether use of the chemical is now 4. Chemicals that are relatively safe on their regulated in Canada. If its use is regulated, own can be much more hazardous when used find out how. together. Find and describe an example of 4 Brainstorm ways to reduce the hazards associated a potentially hazardous drug interaction. with the chemical. You could, for example, decide Doctors, firefighters, hazardous materials to ban it completely, control how it is distributed, specialists, pharmacists, and industrial safety require a permit to purchase or use it, or restrict officers at chemical plants are good resources the quantity that is allowed in products. Use for your research. your ideas to create an action plan for using the chemical. Chapter 2 Names, Formulas, and Properties MHR 61  Section 2.2 Summary In this section, you learned about some of the properties of molecular compounds and ionic compounds. You used your knowledge of bonding to explain some of these properties. You have also explored some of the risks associated with chemicals and their properties. In section 2.3, you will learn about the properties of acids and bases. These substances have some dangerous properties, but they are also very useful. Check Your Understanding 1. Compare and contrast each term in the pairs below. (a) crystal lattice " molecule (b) electrolyte " non-electrolyte 2. Explain why ionic compounds tend to have very high melting points, while molecular compounds tend to have relatively low melting points. Compound Melting 3. Apply Examine the table on the left. The table shows melting points for point sodium fluoride, sodium chloride, and sodium bromide. By examining these sodium fluoride, NaF 993°C melting points, what can you infer about the bonding in each compound? sodium chloride, NaCl 804°C 4. Apply You have been given two solid substances. One of them is sodium bromide, NaBr 755°C an ionic compound, and one is a molecular compound. (a) Describe four safe tests you could perform to try to identify the substances as ionic compounds or molecular compounds. (b) For each test, explain what you would expect to see for an ionic compound, and what you would expect to see for a molecular compound. 5. Thinking Critically Examine the observations in the table below. (a) Use the observations to classify each substance as an ionic compound or a molecular compound. Give reasons to justify your choice. (b) Based on the information in the table, which of the five tests (odour, hardness, ability to dissolve in water, conductivity, or melting point) is the least useful when classifying compounds as ionic or molecular? Explain your answer. Substance Appearance Odour Hardness Dissolves Conductivity Relative Ionic or in water? in aqueous melting point molecular? solution moth balls white solid distinctive soft no cannot be low odour measured sodium white solid none hard and brittle yes conductor high thiosulfate (photographer’s “hypo”) antifreeze colourless “sweet” odour liquid yes non-conductor low liquid potassium deep purple none hard and brittle yes conductor high permanganate crystals benzoic acid white solid distinctive soft a little poor conductor low odour 62 MHR Unit 1 Energy and Matter in Chemical Change 2.3 Properties of Acids and Bases Do your muscles ache after a long workout? Unless you have injured yourself, the ache is probably due to lactic acid. Intense exercise causes the energy- Some anthropods use the releasing process of cell metabolism to surpass the supply of oxygen to your properties of acids to their muscle cells. New chemical reactions begin, releasing the energy you need. advantage. For example, milli- pedes and scorpions produce These reactions also produce lactic acid. Unfortunately, lactic acid reduces corrosive acids to deter predators. the ability of muscle tissue to contract — and causes you pain. Ants secrete drops of an acid to You have seen how to classify compounds as molecular or ionic. There are mark their pathways. other useful ways to classify compounds. You can group them based on their chemical and physical properties. Acids form a very important and common group of chemicals with distinctive and useful properties. The tangy flavour of some fruits and other foods and drinks is due to one physical property of acids: their sour taste. Acids are used to remove rust and to refine and process metals. Acids can perform these functions because of their useful and sometimes dangerous chemical properties. Bases are bitter-tasting compounds with a slippery feel. The bitterness of tonic water is due to a base called quinine. Like acids, bases have useful, distinctive properties. Many cleaning products are bases. So are medical drugs such as lidocaine, a local anaes- thetic used by dentists. Because they are corrosive, however, bases must always be handled with care. Common household acids and bases are shown in Figure 2.7. Defining Acids How do chemists explain the properties of acids and bases? In 1884, the Swedish chemist Svanté Arrhenius (1859–1927) proposed a theory of acids and bases based on their behaviour in water. Pure water, a molecular compound, does not conduct electricity. Both acidic and basic solutions, however, are electrolytes, so they must contain freely moving ions. One common feature of acids is that they all contain hydrogen. Figure 2.7 All these consumer products contain acids and bases. Therefore, Arrhenius defined an acid as a substance that reacts Which of them have you used? and releases hydrogen ions, H!(aq), in a water solution. Did you check the packages for One molecule of hydrogen chloride gas, HCl(g), forms the ions safety warnings? How did you H!(aq) and Cl"(aq) in water. This change is shown below. According change your behaviour after to Arrhenius’s definition, hydrogen chloride dissolved in water, HCl(aq), reading the warnings? is acidic. HCl(g) → H!(aq) ! Cl"(aq) Table 2.9 gives examples of some important acids and their uses. Chapter 2 Names, Formulas, and Properties MHR 63  Table 2.9 Some Important Acids Name Formula Notes sulfuric acid H2SO4(aq) most widely used industrial chemical present in automobile batteries one component of acid precipitation hydrochloric acid HCl(aq) sold in hardware stores as muriatic acid used in water treatment and processing of metals nitric acid HNO3(aq) used to manufacture fertilizers, explosives, and dyes one component of acid precipitation carbonic acid H2CO3(aq) present in rainwater and carbonated drinks ethanoic acid CH3COOH(aq) commonly called white vinegar and used in the home (acetic acid) Defining Bases Arrhenius defined a base as a substance that dissolves in water and releases Pure water contains equal, hydroxide ions, OH"(aq), into the solution. Sodium hydroxide, NaOH(s), for minute quantities of hydrogen example, is an ionic compound that dissolves readily. The number of hydroxide ions and hydroxide ions. In any ions in the solution increases as NaOH(s) crystals break up into ions in solution. pure sample of water, an extremely tiny proportion of the H2O(!) Arrhenius’s theory, therefore, correctly predicts that the solution, NaOH(aq), molecules are ionized. That is, will be basic. One formula unit of solid sodium hydroxide, NaOH(s), dissolves they are broken into a hydrogen in water to form OH–(aq) and Na!(aq), as shown below. According to Arrhenius’s ion (H!(aq)) and a hydroxide ion definition, sodium hydroxide dissolved in water, NaOH(aq), is basic. (OH"(aq)). As a result, the amounts of the two ions in any given NaOH(s) → Na!(aq) ! OH–(aq) sample of pure water are equal. Table 2.10 gives more important information about several useful bases. Table 2.10 Some Important Bases Name Formula Notes sodium hydroxide NaOH(aq) common name is lye most widely used industrial base present in drain cleaners potassium hydroxide KOH(aq) used to make some liquid soaps calcium hydroxide Ca(OH)2(aq) used to manufacture paper and cement magnesium hydroxide Mg(OH)2(aq) not very soluble in water active ingredient in some antacids ammonium hydroxide NH4OH(aq) used to make fertilizer and cleaning solutions Indicators and pH Many common acids and bases form colourless solutions. These look just like water but may be much more hazardous. One safe way to tell whether a solution is acidic or basic is to use an acid-