Chemical Reactions: Displacement, Double Displacement, and Oxides PDF

SIMPLE DISPLACEMENT/SINGLE DISPLACEMENT: The chemical reactions in which a more reactive element displaces a less reactive element from a compound is known as Displacement Reactions. Displacement reactions are also known as Substitution Reaction or Single Displacement/ replacement reactions...

SIMPLE DISPLACEMENT/SINGLE DISPLACEMENT: The chemical reactions in which a more reactive element displaces a less reactive element from a compound is known as Displacement Reactions. Displacement reactions are also known as Substitution Reaction or Single Displacement/ replacement reactions. A general displacement reaction can be represented by using a chemical equation as follows: A + BC → AC + B Displacement reaction takes place only when ‘A’ is more reactive than B. If ‘B’ is more reactive than ‘A’, then ‘A’ will not displace ‘C’ from ‘BC’ and reaction will not be taking place. NOTE: In this general reaction, element A is a metal that replaces element B, also a metal, in the compound. When the element that is doing the replacement is a nonmetal, it must replace another nonmetal in a compound, and the general equation becomes: Y+XZ→XY+Z Y is a nonmetal and replaces the nonmetal Z in the compound with X. Examples: 1) Fe + CuSO4 → FeSO4 + Cu 2) 2AgNO3 + Cu → 2Ag + Cu (NO3)2 3) Zn + 2HCl → ZnCl2 + H2 4) Ca + 2H2O → Ca (OH)2 + H2 ACTIVITY SERIES/REACTIVITY SERIES: What is the Reactivity Series? The reactivity series of metals, also known as the activity series, refers to the arrangement of metals in the descending order of their reactivities. PRINCIPLE OF SIMPLE DISPLACEMENT: Higher the position of the element in the activity series the very reactive it is. The element will displace the element from the compound if it is more reactive than it. 1 DISPLACEMENT THROUGH EXAMPLES: COPPER AND SILVER NITRATE REACTION EQUATION: Cu + 2AgNO3  Cu(NO3)2+ 2Ag OBSERVATION: The solution turns blue Greyish white (Silvery or silver coloured) metal deposited/formed IRON AND COPPER SULPHATE REACTION EQUATION: Fe + CuSO4  FeSO4 + Cu OBSERVATION: The blue solution turns light green Reddish brown /Reddish pink metal deposited/formed ZINC AND LEAD NITRATE REACTION EQUATION: Zn + Pb (NO3)2  Zn (NO3)2 + Pb OBSERVATION: Dark grey solid deposit formed on Zinc NOTE: Zinc is silvery white in colour MAGNESIUM AND COPPER SULPHATE REACTION EQUATION: Mg + CuSO4  MgSO4 + Cu OBSERVATION: The blue solution turns colourless Reddish brown /Reddish pink metal deposited/formed 2  ALUMINIUM AND COPPER SULPHATE REACTION EQUATION: Al + CuSO4  Al2(SO4)3 + Cu OBSERVATION: The blue solution turns colourless Reddish brown /Reddish pink metal deposited/formed OTHER EXAMPLES METAL + COLD WATER REACTION 2Na + H2O (cold) → 2NaOH + H2↑ 2K + H2O (cold) → 2KOH + H2↑ The reaction is highly exothermic. Hydrogen gas ignites. The metals dart over water and burn with characteristic flame- Sodium with Golden yellow flame and Potassium with Lilac flame. OBSERVATION: Brisk effervescence of a colourless gas which produces pop sound when a burning splinter is shown The metals dart over water and burn with characteristic flame- Sodium with Golden yellow flame and Potassium with Lilac flame. Ca + 2H2O (cold) → Ca(OH)2 + H2↑ OBSERVATION: Brisk effervescence of a colourless gas which produces pop sound when a burning splinter is shown METAL + HOT WATER REACTION Mg + H2O (steam) → MgO + H2 ↑ 3Al + 3H2O (steam) → Al2O3 + 3H2 ↑ Zn + H2O (steam) → ZnO + H2 ↑ Fe + H2O (steam) ⇄ Fe3O4 + H2 ↑ OBSERVATION: Brisk effervescence of a colourless gas which produces pop sound when a burning splinter is shown NOTE: METALS BELOW HYDROGEN (COPPER, MERCURY, SILVER, GOLD, PLATINUM) CANNOT DISPLACE HYDROGEN. METAL + DILUTE ACID REACTION With Dilute HCl: 2Na + HCl (dil) → 2NaCl + H2↑ 2K + HCl (dil) → 2KCl + H2↑ Ca + 2HCl (dil) → CaCl2 + H2↑ Mg + 2HCl (dil) → MgCl2 + H2 ↑ 3  2Al + 6HCl (dil) → 2AlCl3 + 3H2 ↑ Zn + 2HCl (dil) → ZnCl2 + H2 ↑ Fe + HCl (dil) → FeCl2 + H2 ↑ With Dilute H2SO4: 2Na + H2SO4 (dil) → Na2SO4 + H2↑ 2K + H2SO4 (dil) → K2SO4 + H2↑ Ca + H2SO4 (dil) → CaSO4 + H2↑ Mg + H2SO4 (dil) → MgSO4 + H2↑ 2Al + 3H2SO4 (dil) → Al2(SO4)3 + 3H2↑ Zn + H2SO4 (dil) → ZnSO4 + H2↑ Fe + H2SO4 (dil) → FeSO4 + H2↑ OBSERVATION: Brisk effervescence of a colourless gas which produces pop sound when a burning splinter is shown NOTE: METALS BELOW HYDROGEN (COPPER, MERCURY, SILVER, GOLD, PLATINUM) CANNOT DISPLACE HYDROGEN. DOUBLE DISPLACEMENT/DOUBLE DECOMPOSITION: A double displacement reaction is a chemical reaction in which two reactants exchange ions to form two new compounds. Double displacement reaction takes the form: AB + CD → AD + CB The two types of double replacement reactions are Precipitation reaction Neutralization reaction PRECIPITATION REACTION: Reaction that takes place between two water soluble solutions of salt or alkali and results in the formation of an insoluble salt (solid) is called precipitation reaction. Eg: AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl ↓(white) Pb(NO3)2(aq) + KI(aq) → PbI2↓(yellow) + KNO3(aq) H2SO4(aq) + BaCl2(aq) → HCl(aq) + BaSO4↓(white) H2SO4(dil) + BaCl2 (aq) → HCl (dil) + BaSO4 ↓ (white) ZnSO4(aq) + 2NaOH(aq) → Zn(OH)2 ↓(white) + Na2SO4 4  Pb(NO3)2(aq) + 2NaOH(aq) → Pb(OH)2 ↓(white) + 2NaNO3 CuSO4(aq)(blue) + 2NaOH(aq) → Cu(OH)2 ↓(pale blue) + Na2SO4 FeSO4(aq)(light green/pale green) + 2NaOH(aq) → Fe(OH)2 ↓(dirty green) + Na2SO4 Fe2(SO4)3 (aq)(reddish brown) + 2NaOH(aq) → Fe(OH)3 ↓(reddish brown) + Na2SO4 NEUTRALIZATION REACTION: The reaction between an acid and a base is called neutralisation reaction. Acid + Metal oxide → Salt + water HCl(dil) + MgO → MgCl2 + H2O 2HNO3(dil) + MgO → Mg(NO3)2 + H2O H2SO4(dil) + MgO → MgSO4 + H2O Acid + Metal hydroxide → Salt + water 2HCl(dil) + Mg(OH)2 → MgCl2 + H2O 2HNO3(dil) + Mg(OH)2 → Mg(NO3)2 + 2H2O H2SO4(dil) + Mg(OH)2 → MgSO4 + 2H2O APPLICATIONS OF NEUTRALISATION: ANTACIDS: Stomach contains hydrochloric acid to help prevent infection and digest food. Sometimes there can be too much acid in your stomach due to indigestion causing acid reflux. Indigestion medicines (antacids) contain an alkali such as Magnesium hydroxide that helps to neutralise the excess acid. Mg (OH)2 + HCl (dil) → MgCl2 + H2O TOOTH PASTES: Most food particles are acidic in nature. For example, lemonade, chocolate, etc. Such foods produce acid in our mouth which reacts with enamel i.e. calcium phosphate and leads to cavities. Using toothpaste while brushing helps to neutralize the acid since toothpaste is a base. FERTILISERS: Plants don’t grow well if the soil is too acidic or too basic. To neutralize acidic soils, basic fertilizers like the ash of burnt wood, CaO, CaCO3(chalk), etc are added. Similarly, basic soils are neutralized by adding decaying organic matter. TO TREAT BEE STINGS/ANT BITES: Bee stings/Ant bites contain formic acid and are acidic in nature, these stings can be neutralized by applying a base like baking soda. TO TREAT WASP STINGS: Wasp sting’s venom is basic in nature, applying vinegar to the sting neutralizes the sting as vinegar is acidic in nature. 5  OXIDES Compounds of oxygen with other elements are called oxides. There are only two kinds of atoms in oxides: NO2, SO2, H2O, CO2, N2O5, NO, N2O are common non-metal oxides. They have covalent bond structure Na2O, FeO, Al2O3, CaO, MgO, CuO, PbO are some common metal oxides. They have ionic structure PREPARATION OF OXIDES: By direct combination of metals and non-metals: 2Mg + O2  2MgO 2C + O2  2CO2 By Thermal decomposition of metal carbonates: CaCO3  CaO + CO2 By Thermal decomposition of metal nitrates: 2Pb(NO3)2  2PbO + 4NO2 + O2 TYPES OF OXIDES ACIDIC OXIDES: Acidic oxides are the oxides of non-metals. These oxides produce acid when combined with water. Examples include sulphur dioxide (SO2), carbon dioxide (CO2), and sulphur trioxide (SO3). Acidic oxides are also known as acid anhydrides. SO2+H2O→H2SO3(l) Sulphurous acid SO3+H2O→H2SO4(l) Sulphuric acid CO2+H2O→H2CO3(l) Carbonic acid They turn moist blue litmus paper red/Blue litmus solution red They turn Alkaline phenolphthalein solution (which is pink in colour) to colourless BASIC OXIDES Basic oxides are the oxides of metals. These oxides produce a base when combined with water. Examples include calcium oxide (CaO), magnesium oxide (MgO), and sodium oxide (Na2O). If soluble in water, they react with water to produce hydroxides called alkalis e.g., 6  CaO+H2O→Ca (OH)2 K2O+H2O→KOH Na2O+H2O→2NaOH These metallic oxides are known as basic anhydrides. They turn moist red litmus paper blue/Red litmus solution blue They turn phenolphthalein solution (which is colourless) pink AMPHOTERIC OXIDES These are metal oxides. These oxides have both acidic and basic properties. They react with both acids and bases to produce water and salts. Examples include Zinc oxide (ZnO), Lead oxide (PbO) and Aluminium oxide (Al2O3). Metals that display amphoteric nature include copper, zinc, lead, tin and aluminum. Their oxides and hydroxides are also amphoteric. ▪ ZnO + 2HCl (dil) → ZnCl2 + H2O (BASIC NATURE) ▪ ZnO + NaOH (conc) → Na2ZnO2 + H2O (ACIDIC NATURE) ▪ PbO + 2HCl (dil) → PbCl2 + H2O (BASIC NATURE) ▪ PbO + NaOH (conc) → Na2PbO2 + H2O (ACIDIC NATURE) ▪ Al2O3 + 6HCl (dil) → 2AlCl3 + 3H2O (BASIC NATURE) ▪ Al2O3 + 2NaOH (conc) → 2NaAlO2 + H2O (ACIDIC NATURE) Amphoteric oxides do not change the colour of litmus paper because of their amphoteric nature. NEUTRAL OXIDES They are oxygen poor compounds of nonmetals. They have neither acidic no basic property. They have no effect on litmus paper. They do not react with acids, bases and water. They are slightly soluble in water. E.g: CO (carbon monoxide), NO (nitric oxide/Nitrogen monoxide), and N2O (Nitrous oxide/Dinitrogen monoxide) 7