9666-1 - Page 1 Name: 1) What is the oxidation number of chromium in the chromate ion, CrO 2-4? A) +8 B) +3 C) +2 D) +6 2) What is the oxidation number of sulfur in Na 2 S 2 O 3? A) +6 B) +4 C) +2 D) -1 3) In a redox reaction, the total number of electrons lost is A) equal to the total number of electrons gained B) less than the total number of electrons gained C) equal to the total number of protons gained D) greater than the total number of electrons gained 4) Half-reactions can be written to represent all A) fission and fusion reactions B) oxidation and reduction reactions C) double-replacement reactions D) neutralization reactions 5) Which balanced equation represents an oxidation-reduction reaction? A) CaCO 3 CaO + CO 2 B) C + H 2 O CO + H 2 C) BaCl 2 + Na 2 SO 4 BaSO 4 + 2NaCl D) Mg(OH) 2 + 2HNO 3 Mg(NO 3 ) 2 + 2H 2 O 6) Which of the following balanced equations represents a redox reaction? A) AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) B) H 2 CO 3 (aq) H 2 O(l) + CO 2 (g) C) NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) D) Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) 7) During which process does an atom gain one or more electrons? A) reduction B) oxidation C) neutralization D) transmutation 8) Which changes occur when Pt 2+ is reduced? A) The Pt 2+ gains electrons and its oxidation number increases. B) The Pt 2+ loses electrons and its oxidation number increases. C) The Pt 2+ loses electrons and its oxidation number decreases. D) The Pt 2+ gains electrons and its oxidation number decreases. 9) Which half-reaction correctly represents reduction? A) Mn 4+ + 3e - Mn 7+ B) Mn 4+ Mn 3+ + e - C) Mn 4+ + e - Mn 3+ D) Mn 4+ Mn 7+ + 3e - 10) Which half-reaction equation represents the reduction of a potassium ion? A) K + + e - K C) K + K + e - B) K + e - K + D) K K + + e - 11) Given the balanced ionic equation representing a reaction: 2Al 3+ (aq) + 3Mg(s) 3Mg 2+ (aq) + 2Al(s) In this reaction, electrons are transferred from A) Al 3+ to Mg C) Mg 2+ to Al B) Al to Mg 2+ D) Mg to Al 3+ 12) Given the balanced equation representing a reaction: Fe 2 O 3 + 2Al Al 2 O 3 + 2Fe During this reaction, the oxidation number of Fe changes from A) +3 to 0 as electrons are transferred B) +3 to 0 as protons are transferred C) +2 to 0 as electrons are transferred D) +2 to 0 as protons are transferred 13) Which of the following reactions occurs spontaneously? A) I 2 (s) + 2NaBr(aq) Br 2 (l) + 2NaI(aq) B) I 2 (s) + 2NaF(aq) F 2 (g) + 2NaI(aq) C) Cl 2 (g) + 2NaBr(aq) Br 2 (l) + 2NaCl(aq) D) Cl 2 (g) + 2NaF(aq) F 2 (g) + 2NaCl(aq) 14) Which of the following half-reactions shows conservation of charge? A) Cu + e - Cu + C) Cu + Cu + e - B) Cu 2+ + 2e - Cu D) Cu 2+ Cu + 2e - 15) Given the balanced equation representing a reaction: Mg(s) + Ni 2+ (aq) Mg 2+ (aq) + Ni(s) What is the total number of moles of electrons lost by Mg(s) when 2.0 moles of electrons are gained by Ni 2+ (aq)? A) 1.0 mol B) 4.0 mol C) 3.0 mol D) 2.0 mol
16) Which conversion of energy always occurs in a voltaic cell? A) light energy to chemical energy B) electrical energy to chemical energy C) chemical energy to electrical energy D) chemical energy to light energy 17) Given the balanced equation representing the reaction occurring in a voltaic cell: 9666-1 - Page 2 20) The diagram below represents an operating electrochemical cell and the balanced ionic equation for the reaction occurring in the cell. Zn(s) + Pb 2+ (aq) Zn 2+ (aq) + Pb(s) In the completed external circuit, the electrons flow from A) Zn(s) to Pb(s) B) Pb(s) to Zn(s) C) Zn 2+ (aq) to Pb 2+ (aq) D) Pb 2+ (aq) to Zn 2+ (aq) 18) Given the balanced ionic equation representing the reaction in an operating voltaic cell: Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) The flow of electrons through the external circuit in this cell is from the A) Zn cathode to the Cu anode B) Zn anode to the Cu cathode C) Cu cathode to the Zn anode D) Cu anode to the Zn cathode 19) A student collects the materials and equipment below to construct a voltaic cell. d two 250-mL beakers d wire and a switch d one strip of magnesium d one strip of copper d 125 ml of 0.20 M Mg(NO 3 ) 2 (aq) d 125 ml of 0.20 M Cu(NO 3 ) 2 (aq) Which additional item is required for the construction of the voltaic cell? A) a cathode B) a salt bridge C) an anode D) a battery Which statement identifies the part of the cell that conducts electrons and describes the direction of electron flow as the cell operates? A) Electrons flow through the wire from the Ni(s) to the Zn(s). B) Electrons flow through the salt bridge from the Zn(s) to the Ni(s). C) Electrons flow through the salt bridge from the Ni(s) to the Zn(s). D) Electrons flow through the wire from the Zn(s) to the Ni(s). 21) Which of the following statements describes electrolysis? A) Chemical energy is used to produce an electrical change. B) Thermal energy is used to produce a chemical change. C) Electrical energy is used to produce a chemical change. D) Chemical energy is used to produce a thermal change. 22) Which of the following statements describes one characteristic of an operating electrolytic cell? A) It requires an external energy source. B) It undergoes a spontaneous redox reaction. C) It produces electrical energy. D) It uses radioactive nuclides. 23) Given the balanced equation representing a reaction occurring in an electrolytic cell: 2NaCl(l) 2Na(l) + Cl 2 (g) Where is Na(l) produced in the cell? A) at the anode, where oxidation occurs B) at the cathode, where oxidation occurs C) at the cathode, where reduction occurs D) at the anode, where reduction occurs
24) Reduction occurs at the cathode in A) voltaic cells, only B) neither electrolytic cells nor voltaic cells C) electrolytic cells, only D) both electrolytic cells and voltaic cells 25) Which statement is true about oxidation and reduction in an electrochemical cell? A) Oxidation occurs at the anode and reduction occurs at the cathode. B) Both occur at the cathode. C) Both occur at the anode. D) Oxidation occurs at the cathode and reduction occurs at the anode. 26) What is the oxidation number of nitrogen in NO(g)? 9666-1 - Page 3 30) A student places a 2.50-gram sample of magnesium metal in a bottle and fits the bottle with a 2-hole stopper as shown in the diagram below. Hydrochloric acid is added to the bottle, causing a reaction. As the reaction proceeds, hydrogen gas travels through the tubing to an inverted bottle filled with water, displacing some of the water in the bottle. 27) The unbalanced equation below represents the decomposition of potassium chlorate. KClO 3 (s) KCl(s) + O 2 (g) Determine the oxidation number of chlorine in the reactant of the given equation. Questions 28 and 29 refer to the following: In a laboratory investigation, magnesium reacts with hydrochloric acid to produce hydrogen gas and magnesium chloride. This reaction is represented by the unbalanced equation below. Mg(s) + HCl(aq) H 2 (g) + MgCl 2 (aq) 28) State, in terms of the relative activity of elements, why the reaction shown is spontaneous. Identify the type of chemical reaction that occurs when magnesium reacts with hydrochloric acid. Questions 31 through 33 refer to the following: The diagram below shows a voltaic cell with copper and aluminum electrodes immediately after the external circuit is completed. 29) Write a balanced half-reaction equation for the oxidation that occurs in the given equation. 31) Balance the redox equation below, using the smallest wholenumber coefficients. Cu 2+ (aq) + Al(s) Cu(s) + Al 3+ (aq)
32) As the voltaic cell shown in the diagram operates, the mass of the Al(s) electrode decreases. Explain, in terms of particles, why the decrease in mass occurs. 33) Explain the function of the salt bridge shown in the diagram. 34) Identify the anode in the cell shown. 9666-1 - Page 4 35) Write a balanced half-reaction equation for the reduction that occurs in the cell shown. Questions 34 and 35 refer to the following: The diagram below represents an operating voltaic cell at 298 K and 1.0 atmosphere in a laboratory investigation. The reaction occurring in the cell is represented by the balanced ionic equation below. 36) In a laboratory investigation, a student constructs a voltaic cell with iron and copper electrodes. Another student constructs a voltaic cell with zinc and iron electrodes. Testing the cells during operation enables the students to write the balanced ionic equations below. Cell with iron and copper electrodes: Cu 2+ (aq) + Fe(s) Cu(s) + Fe 2+ (aq) Cell with zinc and iron electrodes: Fe 2+ (aq) + Zn(s) Fe(s) + Zn 2+ (aq) Write a balanced half-reaction equation for the reduction that takes place in the cell with zinc and iron electrodes. Questions 37 and 38 refer to the following: A voltaic cell with magnesium and copper electrodes is shown in the diagram below. The copper electrode has a mass of 15.0 grams. When the switch is closed, the reaction in the cell begins. The balanced ionic equation for the reaction in the cell is shown beneath the cell diagram. After several hours, the copper electrode is removed, rinsed with water, and dried. At this time, the mass of the copper electrode is greater than 15.0 grams.
37) State the direction of electron flow through the wire between the electrodes when the switch in the given diagram is closed. 9666-1 - Page 5 38) Explain, in terms of copper ions and copper atoms, why the mass of the copper electrode in the given diagram increases as the cell operates. [Your response must include information about both copper ions and copper atoms.] 39) The diagram below shows a system in which water is being decomposed into oxygen gas and hydrogen gas. Litmus is used as an indicator in the water. The litmus turns red in test tube 1 and blue in test tube 2. The oxidation and reduction occurring in the test tubes are represented by the balanced equations below. Test tube 1: 2H 2 O(l) O 2 (g) + 4H + (aq) + 4e - Test tube 2: 4H 2 O(l) + 4e - 2H 2 (g) + 4OH - (aq) Identify the information in the given diagram that indicates the system shown is an electrolytic cell.