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Chem30 Unit 1 – REDOX UA

1. List three aqueous ions that may either gain or lose electrons in a redox reaction.

2. Identify which of the following reactions are spontaneous under standard conditions. Explain why this reaction is spontaneous.

a) Co2+(aq) + 2Fe2+(aq) Co(s) + 2Fe3+(aq)

b) Sn4+(aq) + 2Br-(aq) Sn2+(aq) + Br2(l)

c) 2I-(aq) + Cl2(g) I2(s) 2 Cl-(aq)

d) Pb(s) + Fe2+(aq) Pb2+(aq) + Fe(s)

3. Two of the reagents below will oxidize Pb(s) to Pb2+(aq), but will not oxidize I-(aq) to I2(s). Identify the reagents and explain why they will oxidize lead and not iodine ions.

a) F2(g) and Fe3+(aq)

b) Fe3+(aq) and Br2(l)

c) Cd2+(aq) and Sn4+(aq)

d) Cu2+(aq) and Sn4+(aq)

4. The oxidation numbers of carbon in HCOOH(aq), C6H12O6(s), CO2(g) and CHCl3(g), respectively, are ______.

5. Identify the oxidation number of each atom below. In which substance does sulphur have an oxidation state of zero?

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a) SO3(g)

b) S8(s)

c) H2SO4(aq)

d) Na2SO3(s)

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6. During respiration, our body’s cells metabolize glucose according to the equation

C6H12O6(aq) + 6O2(g) 6HOH(l) + 6CO2(aq)

In the above reaction, is the glucose reduced or oxidized? Explain using your knowledge of electrochemistry.

7. Chlorine gas has an irritating odor and can cause lung damage. To prevent chlorine from escaping into the air, it can be bubbled through Na2S2O3(aq).The unbalanced reaction that occurs is

Cl2(g) + S2O32-(aq) + H2O(l) SO42-(aq) + H+(aq) + Cl-(aq)

a) Identify which compounds are being reduced and oxidized in the reaction above. Label the oxidizing agent and reducing agent.

b) Balance the equation using the oxidation numbers approach. Show all work.

8. Talon Tapes of Edmonton manufactures plastic tape containing small pieces of magnesium. This tape is completely wrapped around iron pipes that will be buried underground. Explain in chemical terms the purpose(s) of each component of the tape. Your response should include relevant half-reactions.

Use the following information to answer the next 4 questions

Titration is an important procedure in the analysis of water samples. One common test is a water hardness test, which determines the concentration of dissolved metals such as calcium. A sample of water is titrated using tetrasodium EDTA, Na4C10H12O8N2(aq). The tetrasodium EDTA reacts with the Ca2+(aq) to form a soluble complex. This change can be detected by using the indicator murexide, C8H8N6O6(aq), which changed from an initial red color to a final purple color.

9. Write the balanced chemical equation for this reaction between tetrasodium EDTA and calcium ions.

Use the titration data below to answer the next two questions

Trial / I / II / III / IV / V
Volume of water sample (mL) / 100.0 / 100.0 / 100.0 / 100.0 / 100.0
Concentration of tetrasodium EDTA (mol/L) / 0.125 / 0.125 / 0.125 / 0.125 / 0.125
Initial volume of tetrasodium EDTA (mL) / 50.00 / 50.00 / 50.00 / 50.00 / 50.00
inal volume of tetrasodium EDTA (mL) / 47.18 / 41.80 / 46.97 / 47.12 / 47.01
Final color of solution / purple / red / purple / purple / purple

10. The volume of tetrasodium EDTA that should be used in calculating the “hard water” concentration is _____ mL. (2.93 mL)

11. Assuming the “hardness of the water” is due solely to dissolved calcium, the concentration of Ca2+(aq) is ______mmol/L. (0.366 mmol/L)

12. What is the oxidation state of H+(aq)in murexide?

13. In the equation Au3+(aq) + 3 NO2(g) + 3H2O(l) Au(s) + 3 NO3-(aq) + 6 H+(aq), which species is the oxidizing agent? The reducing agent? Which is being oxidized? Which is being reduced?

14. Household bleach (sodium hypochlorite solution) will remove iodine stains from clothing. The reaction occurs in a basic medium that prevents the formation of hypochlorous acid. The unbalanced redox reaction is

I2(s) + ClO-(aq) + OH(aq)- Cl-(aq) + IO3-(aq) + H2O(l)

a) Using oxidation numbers, balance the reaction. Calculate the volume of 0.550 mol/L NaClO(aq) solution required to completely react with 1.15 g of I2(s).(41.2 L)

b) Describe the safety procedures that should be followed in the storage and use of bleach. Explain why these safety procedures should be followed. Your response must include appropriate half-reactions and/or chemical equations.

Use the following information to answer the next question.

15. In which test tubes will a spontaneous reaction occur? Support your answer using appropriate half-reactions.

16. LD has made himself a nice solution of 150 mol/L hydrochloric acid. He wants to store it in a metal container. He has four choices for a container: gold, zinc, lead and magnesium. Assuming cost and availability is not an issue, which container should LD use and why? Cite appropriate half-reactions in you answer.

Use the following information to answer the next question.

1 Reacts spontaneously with Cu2+(aq)

2 Reacts spontaneously with Cl-(aq)

3 Is an oxidizing agent and reducing agent

4 Is reduced by hydrogen gas

5 Reacts spontaneously with H2O(l)

6 Reacts spontaneously with Ag(s)

17. Match each of the following species with its most appropriate property.

H2O(l) ______Zn(s) ______Sn4+(aq) ______

18. A student wishes to build a small redox table from the elements A2(aq), B2(aq), C2(aq) and D2(aq). The following reactions were observed:

A2(aq) + 2B-(aq) B2(aq) + 2A-(aq)

C2(aq) + 2B-(aq) no reaction

D2(aq) + 2A-(aq) 2D-(aq) + A2(aq)

Using this information, place each of the elements in order from the SOA to the SRA.

19. Hydrogen cyanide is burned according to the following reaction:

4HCN(g) + 9 O2(g) 4CO2(g) +H2O(g) + 4 NO2(g)

Label each atom in the reaction with its oxidation state. What atom does not change its oxidation state?

Use the following information to answer the next question

20. Write a balanced net ionic redox equation for this reaction. Label the SRA and SOA.

21. A researcher wants to test aluminum, zinc, chromium and copper individually for their suitability as a dental filling. Keeping in mind many foods are acidic, which metal would be the best filling material? Explain using appropriate half-reactions.

22. In an analysis to determine the concentration of Sn2+(aq) ions in a tin ore solution, a 25.0 mL sample of the solution is acidified and titrated to a pink endpoint with 40.0 mL of 0.200 mol/L KMnO4(aq). What is the concentration of Sn2+(aq) ions in the sample?(0.800 mol/L)

23. Solutions of tin (II) ions and copper (II) ions are mixed. What, if any, products would be formed? Support your answer with appropriate electrochemical formulas.

24. Balance the following chemical formula using the oxidation numbers method. Show all work. Assume acidic conditions.

Cr2O72-(aq) + I-(aq) Cr3+(aq) + I2(s)