[fobbz]

These redox questions are giving me grief for my upcoming exam, I hope someone can help me out with these questions, as I have no clue.

40. I assumed that O would be the oxidizer? Why is it not so?
41. I tried to balance this as a 1/2 reaction, and I found that I had to add 5 electrons to one side, doesn't that make the ox # 5?




42. By breaking the second reaction into 1/2 reactions, I get Z ---> Z+  +  e- and  Y+  +  e- --> Y. So isn't Z is the strongest oxidizing agent as it is already in this form?
Next would be Y because it's a reduction, as for X I have no clue...

43. ignore I found the answer
44. also ignore





Thanks in advance

answers are... : D , C and C

[Hunter2]

What is your attempt?

40. What is the basic condition to have an redox reaction? What has to be changed?
41. The given solution are strange, but each arsenic will change bei 5
42. Think again, what is oxidation agent and what is reducing agent

[fobbz]

40. So a redox reaction requires a reduction and an oxidation. Therefore by finding the oxidation number of the given answers you can find a reduction/increase in oxidaton number. So basicly I went

K₂Cr₂O₇

2(1) + 2(x) + 7(-2) = 0
solve for x = 6

then on the product side


Cr₂(SO₄)₃

2x + 3(-2) = 0

x = 3

So Cr was reduced.


41. I don't understand the first reaction at all, is it suggesting that there is no reaction because both reactants are reducing agents?
 I now remember that Y⁺ + e^-  Y is a reduction reaction, thus Y⁺ is an oxidizing agent...


42. I did this question like 40.

As  H₃AsO₄

On the reactant side As's oxidation number is 0, and on the product side it is 5, so the oxidation number increased by 5.

[Hunter2]

40 is correct

41. X + Y⁺ noreaction means that if you have X⁺ + Y a reaction would takes place. So X⁺ is stronger oxydation agent as Y.

Y⁺ + Z = Z⁺ + Y shows that Y is stronger as Z.

Which answer can be only the right one now?

42. I would also agree, but the question is trange, they talking about As₄ what means in total 20 electrons are moved. But for one As ithe solution 5 is correct.

[lillybeans]

40. Under most circumstances, oxygen IS a very powerful oxidizing agent but it depends on the equation. Sometimes it can act as a reducing agent. The answer to this is straight forward, just compare oxidation number before/after and see which one is reduced. So the answer is Cr, which goes from +6 to +3.

41. 0 --> 5. Each As in As4 has ON of 0. in H3AsO4, O4 contributes -8, H3 contributes +3, therefore As must be +5 to make the molecule neutral.

42. Remember, strength of oxidizing agent is another way of saying "Which one is most likely to be reduced, from most likely to least likely". From first equation, we see that when X meets Y, X is reduced, thats why there is no reaction (it is already in its natural state!). So X+ is a powerful oxidizing agent, as it oxidizes Y to Y+ and itself has a strong tendency to become reduced to X. When Y+ meets Z however, Y+ became reduced and Z is oxidized. This means Y has a stronger tendency to be reduced (act as an oxidizing agent) and Z has a stronger tendency to be oxidized (act as a reducing agent). I know the terminology can be really confusing at times.

Therefore the answer should be: X+ > Y+ > Z+

44. Answer is D. This is a grade 11 question, it's just stoichiometry. So what you do is you first find out the total number of moles needed for MnO4, which is (0.0241M * 0.0135L = 0.000325 moles). Then you see that the mole ratio for MnO4 : H2O2 is 2 :5, so 0.000325 * (5/2) = 0.000813 moles. Then divide by volume to get H2O2's concentration, which is 0.000813 / 0.01L =  0.0813 M.

[fobbz]

40. Under most circumstances, oxygen IS a very powerful oxidizing agent but it depends on the equation. Sometimes it can act as a reducing agent. The answer to this is straight forward, just compare oxidation number before/after and see which one is reduced. So the answer is Cr, which goes from +6 to +3.

41. 0 --> 5. Each As in As4 has ON of 0. in H3AsO4, O4 contributes -8, H3 contributes +3, therefore As must be +5 to make the molecule neutral.

42. Remember, strength of oxidizing agent is another way of saying "Which one is most likely to be reduced, from most likely to least likely". From first equation, we see that when X meets Y, X is reduced, thats why there is no reaction (it is already in its natural state!). So X+ is a powerful oxidizing agent, as it oxidizes Y to Y+ and itself has a strong tendency to become reduced to X. When Y+ meets Z however, Y+ became reduced and Z is oxidized. This means Y has a stronger tendency to be reduced (act as an oxidizing agent) and Z has a stronger tendency to be oxidized (act as a reducing agent). I know the terminology can be really confusing at times.

Therefore the answer should be: X+ > Y+ > Z+

44. Answer is D. This is a grade 11 question, it's just stoichiometry. So what you do is you first find out the total number of moles needed for MnO4, which is (0.0241M * 0.0135L = 0.000325 moles). Then you see that the mole ratio for MnO4 : H2O2 is 2 :5, so 0.000325 * (5/2) = 0.000813 moles. Then divide by volume to get H2O2's concentration, which is 0.000813 / 0.01L =  0.0813 M.

Fantastic! Thank you so much guys