CONSTRUCTING RELATIVE REACTIVITY TABLES

1. CONSTRUCTING RELATIVEREACTIVITY TABLES

2. we will examine the observations made when a group of elements and their ions are mixed together. • We will then arrange these elements into a table showing relative reactivity. • This could be in terms of the easiest to the most difficult to be oxidized or reduced; or in terms of the best/worst oxidizing agent or reducing agent

3. SAMPLE PROBLEM 1 • Four elements, A, B, C, and D, form diatomic molecules and ions with a 1- charge. • B- + C2 → C- + B2 • A- + C2 → No Reaction • D- + B2 → B- + D2

4. Write the equation for each reduction half reaction. • Arrange the equations in a relative reduction potential table with the easiest to reduce at the top and the hardest to reduce at the bottom. c) Write the equation for each oxidation half reaction. d) Arrange the equations in a relative oxidation potential table with the easiest to oxidize at the top and the hardest to oxidize at the bottom. e) Which is the best oxidizing agent? Which is the best reducing agent?

5. SAMPLE ANSWER 1 • The reduction half reactions are: C2 + 2e- → 2C- B2+ 2e- → 2B- A2+ 2e- → 2A- D2+ 2e- → 2D-

6. b) Equation (2) indicates no reaction. However, this means no forward reaction. The reverse reaction will take place: C- + A2 → A- + C2 • C2 reacts with B-, ∴ C2 is above B2 in table • A2 reacts with C-, ∴ A2 is above C2 • B2 reacts with D-, ∴ B2 is above D2 • This works out to A2 is above C2 , C2 is above B2 , and B2 is above D2 .

7. Table for (b) • Reactivity table for reduction half reactions, easiest to reduce top, hardest on bottom • A2 + 2e- → 2A- • C2 + 2e- → 2C- • B2 + 2e- → 2B- • D2 + 2e- → 2D-

8. c) The oxidation half reactions are: • 2A- → A2 + 2e- • 2C- → C2 + 2e- • 2B- → B2 + 2e- • 2D- → D2 + 2e

9. d) • B- reacts with C2, ∴ B- is above C • C- reacts with A2, ∴ C- is above A • D-reacts with B2, ∴ D- is above B So, D-is above B-, B- is above C-, and C- is above A-. • 2D- → D2 + 2e- • 2B- → B2 + 2e- • 2C- → C2 + 2e- • 2A- → A2 + 2e- e) The best oxidizing agent is the one that is easiest to reduce, A2. The best reducing agent is the one that is easiest to oxidize, D-.

10. SAMPLE PROBLEM 2 • Four metals, Ca, Mn, Pb, and Mg and their ions with a 2+ charges were involved in experiments that gave the following results: 1. Mg + Mn 2+ → Mg 2+ + Mn 2. Mg 2+ + Ca → Mg + Ca 2+ 3. Pb + Mn 2+ → No Reaction

11. a) Write the equation for each reduction half reaction. b) Arrange the equations in a relative reduction potential table with the easiest to reduce at the top and the hardest to reduce at the bottom. c) Write the equation for each oxidation half reaction. d) Arrange the equations in a relative oxidation potential table with the easiest to oxidize at the top and the hardest to oxidize at the bottom.

12. Practice 3 • Experiments were performed with 4 metals and solutions of their positive ions: Zn/Zn2+ , Fe/Fe 2+ ,Ag/Ag +, Cu/Cu 2+ .The following observations were made: i) Fe 2+ + Zn → Fe + Zn 2+ ii) Fe 2+ + Cu → No Reaction iii) 2Ag + + Cu → 2Ag + Cu 2+ • Answer parts a to e, like previous sample problems.