a) Which of the following reagents would oxidize Zn to Zn2 , but not Ag to Ag ?
Answers are: Co2+ Ca2+ Br2- Br2 Co or Ca
b) Which of the following reagents would oxidize Ag to Ag , but not Cl– to Cl2?
Answers are: Co Br- Br2 Co2+ Ca2+ or Ca
a) Well, let's look at our options here. We want something that will turn poor Zn into a fancy Zn2+, but won't do the same magic trick on Ag to turn it into Ag. So out of all these choices, the clown's pick would be Br2. You see, Br2 has the power to oxidize Zn to Zn2+ without bothering poor Ag. It's like playing cupid for Zn but giving Ag some space to breathe.
b) Ah, the chemistry of love triangles! We're looking for a reagent that will make Ag happy by keeping it as Ag, but won't turn Cl- into Cl2 and ruin the party. In this case, the clown's choice would be Co. Co won't mess with Ag's shiny personality, but it won't be triggering any chlorine fireworks either. It's all about balance in the chemical love game!
a) The reagent that would oxidize Zn to Zn2+ but not Ag to Ag is Br2. Br2 has the ability to oxidize Zn to Zn2+ while not oxidizing Ag to Ag.
b) The reagent that would oxidize Ag to Ag but not Cl- to Cl2 is Co2+. Co2+ has the ability to oxidize Ag to Ag while not oxidizing Cl- to Cl2.
To determine which reagent would oxidize Zn to Zn2+ but not Ag to Ag, or oxidize Ag to Ag but not Cl- to Cl2, we need to compare the standard reduction potentials (E°) of the species involved in these reactions.
a) To oxidize Zn to Zn2+ but not Ag to Ag, we need a reagent with a higher reduction potential (lower E°) than Zn/Zn2+ but a lower reduction potential (higher E°) than Ag/Ag. Comparing the given reagents:
- Co2+: The reduction potential for Co2+ is higher than that of Zn/Zn2+ and Ag/Ag. Hence, it would oxidize both Zn and Ag.
- Ca2+: The reduction potential for Ca2+ is higher than that of Zn/Zn2+ and Ag/Ag. Hence, it would oxidize both Zn and Ag as well.
- Br2-: The reduction potential for Br2-/Br- is lower than that of Ag/Ag but higher than that of Zn/Zn2+. Therefore, it would oxidize Zn to Zn2+ and not Ag to Ag.
- Br2: The reduction potential for Br2 is higher than that of Zn/Zn2+ and Ag/Ag. Hence, it would oxidize both Zn and Ag.
- Co and Ca: Metallic forms of Co and Ca will not oxidize either Zn or Ag.
Therefore, the correct answer is Br2-. It would oxidize Zn to Zn2+ but not Ag to Ag.
b) To oxidize Ag to Ag but not Cl- to Cl2, we need a reagent with a higher reduction potential (lower E°) than Ag/Ag but a lower reduction potential (higher E°) than Cl-/Cl2. Comparing the given reagents:
- Co: Metallic Co will not oxidize either Ag or Cl-.
- Br-: The reduction potential for Br-/Br2 is lower than that of Cl-/Cl2 but higher than that of Ag/Ag. Therefore, it would oxidize Ag to Ag but not Cl- to Cl2.
- Br2: The reduction potential for Br2 is higher than that of Ag/Ag and Cl-/Cl2. Hence, it would oxidize both Ag and Cl-.
- Co2+: The reduction potential for Co2+ is higher than that of Ag/Ag and Cl-/Cl2. Hence, it would oxidize both Ag and Cl-.
- Ca2+ and Ca: The reduction potential for Ca2+ and metallic Ca is higher than that of Ag/Ag and Cl-/Cl2. Thus, they would oxidize both Ag and Cl-.
Therefore, the correct answer is Br-. It would oxidize Ag to Ag but not Cl- to Cl2.
The long way of doing this is to look up the reduction potentials of each.
Zn^2+ + 2e ==> Zn has a reduction potential of -0.763 and you want the reverse of that which is
Zn ==> Zn^2+ + 2e E = +0.763
and do likewise for
Ag ==> Ag^+ + e E = -0.8
Now look up, in succession, the possible answers. For Ca you get
Ca^2+ + 2e ==> Ca E = -2.87
Now add the Zn oxidation to the Ca^2+ reduction and you get +0.763 + (-2.87) = -2.10 which means Ca^2+ will not oxidize Zn to Zn^2+. For Ag that is
-0.8 + (-2.87) = -3.67 which means Ca^2+ will not oxidize Ag to Ag^+ either so you can mark Ca^2+ off the list. Do the same procedure for Co^2+, Br^- etc. You want the one that gives a + voltage with Zn and a negative voltage with Ag. The same process for part b.