Unit 4 Review - Chemical Reactions PDF

Unit 4 Review Chemical Reactions  Topic 4.1 - Introduction for Reactions Learning Objective: Identify evidence of chemical and physical changes in matter. Essential Knowledge: ○ A physical change occurs when a substance undergoes a change in properties but not a change i...

Unit 4 Review Chemical Reactions  Topic 4.1 - Introduction for Reactions Learning Objective: Identify evidence of chemical and physical changes in matter. Essential Knowledge: ○ A physical change occurs when a substance undergoes a change in properties but not a change in composition. Changes in the phase of a substance (solid, liquid, gas) or formation/ separation of mixtures of substances are common physical changes. ○ A chemical change occurs when substances are transformed into new substances, typically with different compositions. Production of heat or light, formation of a gas, formation of a precipitate, and/or color change provide possible evidence that a chemical change has occurred.  Physical vs. Chemical Changes Physical Change: matter changes form, but not chemical identity ○ Any phase change is a physical change ○ In the case of a phase change, bonds are not broken or formed, but intermolecular forces can be severed or formed. Chemical Change: a change that creates new substances by the breaking of bonds and the formation of new bonds ○ Also known as a chemical reaction Signs of Chemical Reactions: ○ Color changes ○ Temperature changes (heat or light) ○ Formation of a gas ○ Formation of a precipitate ○ Production of a gas ○ Production of an odor  Video Resources Physical and Chemical Changes - Bozeman: https://www.youtube.com/watch?v=X328AWaJXvI Chemical Changes - Bozeman: https://www.youtube.com/watch?v=oBFVPd9N5SY&disable_polymer=true Physical and Chemical Changes: https://www.youtube.com/watch?v=yIJ2qnUOOwQ  Practice Problems A student mixes silver nitrate and potassium chloride and notices that the solution becomes cloudy. Is this an example of a physical or a chemical change? Explain ○ Chemical change - formation of a precipitate When liquid water evaporates, which of the following is occurring? ○ Bonds between hydrogen and oxygen atoms are being broken ○ Bondings between hydrogen and oxygen atoms are being formed ○ Intermolecular forces between water molecules are being severed ○ Intermolecular forces between water molecules are being formed Which of the following does NOT indicate a chemical change? ○ A colorless solution turns pink ○ When zinc is added to hydrochloric acid, bubbles are produced ○ Heat is produced when hydrogen peroxide is mixed with potassium iodide ○ A beaker of acetone evaporates in the fume hood  Topic 4.2 - Net Ionic Equations Learning Objective: Represent changes in matter with a balanced chemical or net ionic equation: ○ For physical changes ○ For given information about the identity of the reactants and/or products ○ For ions in a given chemical reaction Essential Knowledge: ○ All physical and chemical processes can be represented symbolically by balanced equations. ○ Chemical equations represent chemical changes. These changes are the result of a rearrangement of atoms into new combinations; thus, any representation of a chemical change must contain equal numbers of atoms of every element before and after the change occurred. Equations thus demonstrate that mass is conserved in chemical reactions. ○ Balanced molecular, complete ionic, and net ionic equations are differing symbolic forms used to represent a chemical reaction. The form used to represent the reaction depends on the context in which it is to be used. TIP FOR BALANCING COMBUSTION REACTIONS: BALANCE CARBON FIRST, THEN HYDROGEN, THEN OXYGEN  Representing Chemical Reactions Molecular Equation: a complete balanced equation representing all reactants and products in a chemical reaction. Pb(NO3)2 (aq) + 2NaI(aq) ---> PbI2 (s) + 2NaNO3 (aq) Complete Ionic Equation: a complete balanced equation which separates all ions that participate in the chemical reaction. Pb2+(aq) + 2NO31-(aq) + 2 Na1+ (aq) + 2 I1-(aq) ---> PbI2 (s) + 2 Na1+(aq) + 2 NO31- (aq) Net Ionic Equation: Includes only the species involved in a chemical reaction ○ Does not include spectator ions Pb2+(aq) + 2 I1-(aq) ---> PbI2 (s)  Video Resources Complete and Net Ionic Equations - KHAN: https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichio me/types-of-chemical-reactions/v/complete-ionic-and-net-ionic-equations Writing Net Ionic Equations - ChemistNATE: https://www.youtube.com/watch?v=EQIqcT9a7DY Precipitation Reactions: https://www.youtube.com/watch?v=leCoWeIN-h8  Practice Problems Balance the following equation: Al(OH)3 + H2SO4 ---> Al2(SO4)3 + H2O ○ 2 Al(OH)3 + 3 H2SO4 ---> Al2(SO4)3 + 6 H2O Write and balance the complete molecular equation and net ionic equation for the reaction between potassium phosphate and aluminum nitrate. ○ K3PO4 (aq) + Al(NO3)3 (aq) ---> AlPO4 (s) + 3 KNO3 (aq) ○ Al3+(aq) + PO43- (aq) ---> AlPO4 (s) Sodium fluoride reacts with nitric acid. Write and balance the net ionic equation for this reaction. ○ F-(aq) + H+(aq) ---> HF(s)  Topic 4.3 - Representations of Reactions Learning Objective: Represent a given chemical reaction or physical process with a consistent particulate model. Essential Knowledge: Balanced chemical equations in their various forms can be translated into symbolic particulate representations.  Practice Problems Using the key provided, draw a particulate level diagram for the reaction below:  Topic 4.4 - Physical and Chemical Changes Learning Objective: Explain the relationship between macroscopic characteristics and bond interactions for: ○ Chemical processes ○ Physical processes Essential Knowledge: ○ Processes that involve the breaking and/or formation of chemical bonds are typically classified as chemical processes. Processes that involve only changes in intermolecular interactions, such as phase changes, are typically classified as physical processes. ○ Sometimes physical processes involve the breaking of chemical bonds. For example, plausible arguments could be made for the dissolution of a salt in water, as either a physical or chemical process, involves breaking of ionic bonds, and the formation of ion-dipole interactions between ions and solvent.  Physical Processes and Bond Breaking Sometimes physical processes involve the breaking of chemical bonds. ○ Ex. the dissolution of a salt in water, involves breaking of ionic bonds and the formation of ion-dipole interactions between ions and solvent.  Practice Problems Briefly describe what happens when ammonia evaporates from a beaker that is sitting inside a fume hood. ○ Hydrogen bonds between molecules of ammonia are broken and the molecules begin to separate and leave the liquid phase to enter the gas phase  Topic 4.5 - Stoichiometry Learning Objective: Explain changes in the amounts of reactants and products based on the balanced reaction equation for a chemical process. Essential Knowledge: ○ Because atoms must be conserved during a chemical process, it is possible to calculate product amounts by using known reactant amounts, or to calculate reactant amounts given known product amounts. ○ Coefficients of balanced chemical equations contain information regarding the proportionality of the amounts of substances involved in the reaction. These values can be used in chemical calculations involving the mole concept. ○ Stoichiometric calculations can be combined with the ideal gas law and calculations involving molarity to quantitatively study gases and solutions.  Video Resources Limiting Reactants - KHAN: https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome/limiting -reagent-stoichiometry/v/stoichiometry-limiting-reagent Limiting Reactants - Tyler DeWitt: https://www.youtube.com/watch?v=N0dTXcoHI-I Theoretical and Percent Yield: https://www.youtube.com/watch?v=jtAj0s203CI  Practice Problems According to the balanced equation below, how many moles of copper (II) carbonate are required to react with 30 mL of a 1.5 M sulfuric acid. Cu3(PO4)2 + 3 H2SO4 → 3 CuSO4 + 2H3PO4 ○ 0.015 mols What is the percentage yield of hydrochloric acid if 11.0 g of calcium chloride produces 6.6 g of hydrochloric acid? CaCl2 +2 HBr → CaBr2 + 2 HCl ○ 91% Take the reaction In an experiment, 3.25 g of NH3 are allowed to react with 3.50 g of O2. What is the maximum mass of NO that could be produced? 4NH3 + 5O2 → 4NO + 6H2O. ○ 2.63 g NO  Practice Problems The equation for the complete combustion of methanol is 2 CH3OH(l) + 3 O2(g)---> 2 CO2(g) + 4 H2O(g) If 64 grams of methanol (molar mass 32 g/mol) is combined with 44.8 liters of oxygen, measured at STP, the number of moles of carbon dioxide which can be produced is (A) 0.66 moles (B) 1.3 moles (C) 1.5 moles (D) 4.0 moles  Topic 4.6 - Introduction to Titration Learning Objective: Identify the equivalence point in a titration based on the amounts of the titrant and analyte, assuming the titration reaction goes to completion. Essential Knowledge: ○ Titrations may be used to determine the concentration of an analyte in solution. The titrant has a known concentration of a species that reacts specifically and quantitatively with the analyte. The equivalence point of the titration occurs when the analyte is totally consumed by the reacting species in the titrant. The equivalence point is often indicated by a change in a property (such as color) that occurs when the equivalence point is reached. This observable event is called the endpoint of the titration.  Video Resources What is a titration and how is it preformed?: https://www.youtube.com/watch?v=YqfvRBJ-iPg Redox Titration of Potassium Permanganate and Hydrogen Peroxide: https://www.youtube.com/watch?v=J7Pnqzi4eHc&disable_polymer=true  Titration Vocabulary Titrant: The solution of known concentration Analyte: The solution of unknown concentration Buret: a piece of laboratory glassware used to add small volumes of liquid to a solution  What is a Titration? To perform a titration, the titrant is slowly added to the buret. ○ The buret should first be rinsed with two small portions of the titrant Next, a measured volume of the analyte is added to an erlenmeyer flask and placed under the buret. ○ If an indicator is being used in the titration, several drops of indicator will be added to the analyte Titrant is slowly added to the flask from the buret until the end point is reached ○ The end point is detected when the color of the indicator changes or the desired pH is detected by the pH meter From the amounts of titrant and analyte used, the concentration of the analyte can be determined  Practice Problems A titration was performed using NaOH as the titrant. Using the diagram on the left, how much NaOH was dispensed from the buret? Write your answer using the correct number of significant figures. ○ 31.65 mL (+ or - 0.5 mL) If the concentration of the sodium hydroxide in the previous problem is 0.10 M, calculate the number of moles of OH- that were added to the analyte. ○ 3.2 x 10-3 moles  Topic 4.7 - Types of Chemical Reactions Learning Objective: Identify a reaction as acid-base, oxidation-reduction, or precipitation. Essential Knowledge: ○ Acid-base reactions involve transfer of one or more protons between chemical species. ○ Oxidation-reduction reactions involve transfer of one or more electrons between chemical species, as indicated by changes in oxidation numbers of the involved species. Combustion is an important subclass of oxidation-reduction reactions, in which a species reacts with oxygen gas. In the case of hydrocarbons, carbon dioxide and water are products of complete combustion. ○ In a redox reaction, electrons are transferred from the species that is oxidized to the species that is reduced.  Essential Knowledge (cont): ○ Oxidation numbers may be assigned to each of the atoms in the reactants and products; this is often an effective way to identify the oxidized and reduced species in a redox reaction. ○ Precipitation reactions frequently involve mixing ions in aqueous solution to produce an insoluble or sparingly soluble ionic compound. All sodium, potassium, ammonium, and nitrate salts are soluble in water  Types of Reactions Acid-Base Reactions: involve transfer of one or more protons between chemical species. ○ Example: HCl(aq) + NaOH(aq)→H2O(l) + NaCl(aq) HC2H3O2(aq)+ H2O(l)⇌ C2H3O2−(aq)+ H3O+(aq) Oxidation-Reduction (Redox) Reactions: a type of chemical reaction that involves a transfer of electrons between two species. ○ Example: Fe2+ + Ce4+→ Fe3+ + Ce3+ ○ In this case iron is oxidized and cerium is reduced Precipitation Reactions: a type of chemical reaction in which two soluble salts in aqueous solution combine and one of the products is an insoluble salt ○ Example: AgNO3(aq) + KCl(aq) →AgCl(s) + KNO3(aq)  Rules for Oxidation Numbers Elements in their elemental form have an oxidation number of zero. The oxidation number of a monatomic ion is the same as its charge. Oxygen has an oxidation number of −2, except in the peroxide ion (O22-), in which it has an oxidation number of −1. Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal. Fluorine always has an oxidation number of −1. The other halogens have an oxidation number of −1 when they are negative They can have positive oxidation numbers, most notably in oxyanions The sum of the oxidation numbers in a neutral compound is zero. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.  Solubility Rules While there are many solubility rules that you should be familiar with, the only important rules on the AP exam are that salts that contain any of the following four ions are ALWAYS soluble in water: ○ Sodium (Na+) ○ Potassium (K+) ○ Ammonium (NH4+) ○ Nitrate (NO3_)  Video Resources Introduction to Redox Reactions - KHAN: https://www.khanacademy.org/science/chemistry/oxidation-reduction/redox-oxidation-re duction/v/oxidation-reduction-or-redox-reactions Redox Reactions - Crash Course in Chemistry: https://www.youtube.com/watch?time_continue=253&v=lQ6FBA1HM3s&feature=emb_lo go Assigning Oxidation Numbers - Tyler Dewitt: https://www.youtube.com/watch?v=-a2ckxhfDjQ Descriptions and Examples of the Three Reaction Types: https://chem.libretexts.org/Courses/Oregon_Institute_of_Technology/OIT%3A_CHE_201_- _General_Chemistry_I_(Anthony_and_Clark)/Unit_6%3A_Common_Chemical_Reactions/6.5 %3A_Classifying_Chemical_Reactions_(Redox)  Practice Problems Write and balance the precipitation reaction between silver nitrate and ammonium chloride. ○ AgNO3(aq) + NH4Cl AgCl(s) + NH4NO3(aq) In the following reaction, which element is being oxidized and which element is being reduced? H2O + Cl− + 2 MnO4− → 2 MnO2 + ClO3− + 2 OH− ○ Mn is reduced ; Cl is oxidized Identify the oxidation numbers of the elements in the following compound: (NH4)2SO4 ○ N: -3 H: +1 S: +6 O: -2 What type of reaction occurs when ammonia reacts with water? ○ Acid-Base Reaction What type of reaction occurs when cadmium nitrate reacts with potassium phosphate? ○ Precipitation Reaction  Topic 4.8 - Introduction to Acid-Base Reactions Learning Objective: Identify species as BrønstedLowry acids, bases, and/or conjugate acid-base pairs, based on proton-transfer involving those species. Essential Knowledge: ○ By definition, a Brønsted-Lowry acid is a proton donor and a Brønsted-Lowry base is a proton acceptor. ○ Only in aqueous solutions, water plays an important role in many acid-base reactions, as its molecular structure allows it to accept protons from and donate protons to dissolved species. ○ When an acid or base ionizes in water, the conjugate acid-base pairs can be identified and their relative strengths compared.  Acid and Base Definitions Bronsted-Lowry Acid: substances that are proton donors (H+) Bronsted-Lowry Base: substances that are proton acceptors (H+) ○ Water can be act as a proton donor or a proton acceptor (amphiprotic) Conjugate Acid: the substance that forms after a base gains a proton Conjugate Base: the substance that remains after an acid has donated its protons  Strong Acids and Bases The seven strong acids are: HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3 The strong bases are: LiOH, NaOH, KOH, RbOH, CsOH, Sr(OH)2, Ca(OH)2, Ba(OH)2 The magnitude of the equilibrium constant (Keq)for an ionization reaction can be used to determine the relative strengths of acids and bases. ○ If Keq is greater than 1, the reaction favors the products and the acid or base in the reactants is stronger ○ If Keq is less than 1, the reaction favors the reactants and the acid or base on the products side is stronger  Video Resources Bronsted-Lowry Definition of Acids and Bases - KHAN: https://www.khanacademy.org/science/biology/water-acids-and-bases/acids-bases-and-p h/v/bronsted-lowry-definition-of-acids-and-bases Conjugate Acid-Base Pairs: https://www.youtube.com/watch?v=IeOKzvlFiIk Acid-Base Strength: https://www.youtube.com/watch?v=PdqFSw_SRug  Practice Problems In the reaction 2 HCO3- H2CO3+ CO32- the hydrogen carbonate ion, HCO3- is functioning as: (A) a Bronsted-Lowry acid only. (B) a Bronsted-Lowry base only. (C) both a Bronsted-Lowry acid and a Bronsted-Lowry base. (D) neither a Bronsted-Lowry acid nor a Bronsted-Lowry base. According to the reaction below, what is the strongest acid? HF(aq) + H2O(l) ---> F - (aq) + H3O + (aq) Keq = 7.2 x 10-4 ○ H3O+ According to the reaction below, what is the strongest base? HCl(aq) + NaOH(aq) ---> H2O(l) + NaCl(aq) Keq = 1 x 10 8 ○ NaOH  Topic 4.9 - Oxidation-Reduction (Redox) Reactions Learning Objective: Represent a balanced redox reaction equation using half-reactions. Essential Knowledge: Balanced chemical equations for redox reactions can be constructed from half-reactions  Oxidation vs Reduction An element is oxidized when there is a loss of electrons An element is reduced when there is a gain of electrons Use the mnemonic OIL RIG (Oxidation is Loss - Reduction is Gain)  Video Resources What are Half-Reactions? - ChemistNATE: https://www.youtube.com/watch?v=vDdVWUVe-pY  Practice Problems In the reaction 6 KI + 2 KMnO4+ 4 H2O------> 3 I2+ 2 MnO2+ 8 KOH which atom undergoes oxidation? (A) K (B) Mn (C) O (D) I Write the oxidation and reduction half reactions for the following redox reaction: Zn(s) + CuSO4 (aq) → ZnSO4 (aq) + Cu ○ The oxidation half-reaction can be written as: Zn → Zn2+ + 2e– ○ The reduction half-reaction can be written as: Cu2+ + 2e– → Cu  Practice Problems Balance the following half reactions: Cu2+ → Cu+ Pb2+ →Pb4+ 1e- + Cu2+ → Cu+ Pb2+ →Pb4+ + 2e- Write the complete balanced reaction based on the half reactions above ○ 2 Cu2+ + Pb2+ → 2Cu+ + Pb4+ Unit 4: Chemical Reactions Write This… …Not That! Rationale Net ionic equations only containing species that Aqueous ionic compounds in their Including these is not a net ionic, it’s a molecular or complete ionic change undissociated form, spectator ions Polyatomic ions that are shown as a compound Polyatomic ions that are broken down into Polyatomic ions themselves do not dissociate in solution, they only dissociate from the other ion in with the correct charge in solution elemental ions in solution an ionic compound Net ionic equations with correct species, ionic Net ionic equations that contain incorrect Net ionic equations must correctly represent the ions and other species (ref. 2018 #6a and 2019 #3a) charges and stoichiometric coefficients formulas or ions without associated charges or that are not stoichiometrically balanced Determination of the concentration of an analyte in Applying M1V1=M2V2 as a blanket method for While acid-base titrations are often 1:1, not all titrations (especially REDOX titrations) follow this a titration that takes into account the stoichiometry determining concentration at an end point if the stoichiometry; in situations that are not 1:1, the of the reaction stoichiometry is not 1:1 stoichiometric ratios must be accounted for in calculations (ref. 2018 #3e) Justification of whether a species is A justification of oxidation/reduction that uses Oxidation numbers are assigned to individual atoms in the reaction, and they are not automatically the oxidized/reduced by referencing oxidation charge on an ion same as the charge in a polyatomic ion (ref. 2019 numbers #7a)