[rickyponting66]

Hello,

I got a old redox reactions worksheet, i think its from 1985 paper. I solved, but i do not have answers, can you please solve it for me so that i can match my answers?

It has 17 MCQs attached in docx file below..
thanks for helping!

[Lord Hades]

Too many questions in one shot.....give them as you go...or else not many will answer

[rabolisk]

You haven't attempted all of them. Of the ones you have, 1, 3, and 12 are wrong. Also, are you given a table of standard reduction potentials?

[rickyponting66]

No, i am not given a standard reduction potentials..

Can you please tell me the correct of ones that i solved wrong?

and i'll solve others and will tell you... please correct me..

edit: okay, i have solved all.. Now please correct and give me right answers.. thanks! (file attached)

rabolisk said that 1, 3 and 12 are wrong, please let me know their correct answers.
Also i re-attempted 8, 9, 10 question.. please check them out.

[rabolisk]

1, 3, and 12 are not any different from the rest of the questions you answered correctly. I see no reason you should be having trouble with these. Why did you pick the answers you did?

Your reasons for 10 is like re-stating the obvious. Hydrogen is a reducing agent because it reduces when it reacts? Also, number 3 of 10 is wrong, and your reason, again, is just defining oxidation. Think again.

8 and 9 are correct, although you should explain your reasons.

[rickyponting66]

1, 3, and 12 are not any different from the rest of the questions you answered correctly. I see no reason you should be having trouble with these. Why did you pick the answers you did?

Your reasons for 10 is like re-stating the obvious. Hydrogen is a reducing agent because it reduces when it reacts? Also, number 3 of 10 is wrong, and your reason, again, is just defining oxidation. Think again.

8 and 9 are correct, although you should explain your reasons.

1, 3 and 12 i solved.. Thanks!

As for the 9 (a), my reason is that Ni(NO₃)₂ is an oxidising agent as oxygen is eliminating from it, itself reduced. So oxidising other, thats why its an oxidising agent. . Is this correct?

9 (b), MnO₂ is oxidising agent in it as its loosing oxygen and oxidises other, so itself getting reduced. Hence its an oxiding agent. . Is this correct?

10 (1) True as oxidation state of oxygen reduced, so itself get reduced and oxidises other.. is it correct?

10 (2)  True: as oxidation state of H increases, itself oxidised and reduced other.. is that true?

10 (3) i thought its true, i deducted from equation.. I cant get, if its false then can you please share the reason with me?

Please check now,
Thanks!

[rabolisk]

Those are all correct. I don't see the reason to talk about "oxygen eliminating" in 9. I don't know how you were taught redox, but the simplest and the clearest answer would just be to state that the oxidation state of Ni is changed from +2 to 0.

For 10(3), look at the reaction again, and use the rules for oxidation state. There is a case in which chlorine is not reduced to -1.

[rickyponting66]

For 10(3), look at the reaction again, and use the rules for oxidation state. There is a case in which chlorine is not reduced to -1.

I dont see such case, in both equations, chlorine is changing to -1 i think..

[rabolisk]

You should review the rules for determining oxidation states then. The second reaction contains a chlorine product that is not -1.

[rickyponting66]

You should review the rules for determining oxidation states then. The second reaction contains a chlorine product that is not -1.

So, you must be talking about NaClO in
2NaOH (aq) + Cl₂ (g) --> NaCl (aq)  + NaClO (aq) + H₂O

but can you explain, how it is not -1.. Na has +1, Cl has -1, O has -2, So how it would be done?

[rabolisk]

It's not -1 because if it were -1, NaClO would have to be NaClO^3-. Oxygen is more electronegative than chlorine, and its oxidation state will be -2. Na will be +1. Since the molecule is neutral, Cl has to be +1.

[Vidya]

you can assume oxidation number of Cl as X
Na is +1
O is -2
so
+1 +x + (-2) = 0 ( no charge on NaClO)
then solve it for x and that is the oxidation number of Cl