AAMC Scored C/P #53

[laczlacylaci]

So Zn +2HCl-> ZnCl2 + H2 + Cl2
Zn is (0 to 2+)->>>oxidized
H is (1+ to 0)->>>reduced

2Al + 6HCl-> 2AlCl3 + 3H2
Al is (0 to 3+)->>> oxidized
H is (1+ to 0)->>> reduced

I don't know what I was thinking when I chose C because Cl doesn't change it's oxidation state. (I think I some how formed Cl2)<<--dumb

I think I would have gotten it correct through POE, but I don't understand why the key says a new solid is formed when Al is mixed with Zn2+ (It did not say Zn and Al was in the same beaker).
Why is Al more susceptible to oxidation than Zn? Because of the 3+ charge rather than 2+? If I was given Ecell values, I think I would have concluded this.

Did I need to use this table at all?

---

Members don't see this ad.

 

[laczlacylaci]

View attachment 208610
So Zn +2HCl-> ZnCl2 + H2 + Cl2
Zn is (0 to 2+)->>>oxidized
H is (1+ to 0)->>>reduced

2Al + 6HCl-> 2AlCl3 + 3H2
Al is (0 to 3+)->>> oxidized
H is (1+ to 0)->>> reduced

I don't know what I was thinking when I chose C because Cl doesn't change it's oxidation state. (I think I some how formed Cl2)<<--dumb

I think I would have gotten it correct through POE, but I don't understand why the key says a new solid is formed when Al is mixed with Zn2+ (It did not say Zn and Al was in the same beaker).
Why is Al more susceptible to oxidation than Zn? Because of the 3+ charge rather than 2+? If I was given Ecell values, I think I would have concluded this.

Did I need to use this table at all?
View attachment 208611

I think I got it...
Is it because Al3+ doesn't really want to become a solid (reduction), so it is more prone to oxidation.
Since Zn2+ became a solid more frequency than Al (in the presence of Al), it is more prone to reduction.

 

[theonlytycrane]

The first situation uses Zn(s) and HCl and they say that H2(g) evolves. In this case, H is getting reduced and Zn(s) must be getting oxidized to Zn2+. This means that H2 must have a higher reduction potential than Zn since it gets the electrons.

The question involves Al, but it's really about comparing Al to Zn. Using table 1, we can see that Zn has a higher reduction table than Al. When it was in the Zn(s) form, Al3+ can't reduce it, and when it was in the Zn2+ form it takes the electrons from Al(s).

Since H2(g) has a higher reduction potential than Zn(s) and Zn(s) has a higher reduction potential than Al(s), H2 will also be able to take the electrons from Al(s) so H2(g) will evolve.

 

[betterfuture]

The first situation uses Zn(s) and HCl and they say that H2(g) evolves. In this case, H is getting reduced and Zn(s) must be getting oxidized to Zn2+. This means that H2 must have a higher reduction potential than Zn since it gets the electrons.

The question involves Al, but it's really about comparing Al to Zn. Using table 1, we can see that Zn has a higher reduction table than Al. When it was in the Zn(s) form, Al3+ can't reduce it, and when it was in the Zn2+ form it takes the electrons from Al(s).

Since H2(g) has a higher reduction potential than Zn(s) and Zn(s) has a higher reduction potential than Al(s), H2 will also be able to take the electrons from Al(s) so H2(g) will evolve.

Can you explain that again. You said Zn + HCl --> H2 (g) + Zn2+ (In this case Zn (s) is oxidized and HCl is reduced.) How do we know again which one has the higher reduction potential or not?

An how did you figure that about Al? I guessed on that question but got it right but I want to make sure I understand it.

 

[laczlacylaci]

Can you explain that again. You said Zn + HCl --> H2 (g) + Zn2+ (In this case Zn (s) is oxidized and HCl is reduced.) How do we know again which one has the higher reduction potential or not?

An how did you figure that about Al? I guessed on that question but got it right but I want to make sure I understand it.

If you look at the table, if something becomes a solid (Al or Zn) it is being reduced. (ie. Zn2+ to Zn (O.S.: 2+ to 0, gained e- : reduction)
In table 1, it says Al3+ and Zn has no change=Al3+ likes to stay as Al3+ (oxidized)
In the row of Zn, Zn2+ becomes a solid in Al, so it wants to become Zn (s) (being reduced)
This is why you know Al wants to be oxidized more than Zn.

 

[betterfuture]

Thank God I did some quick review on Electrochemistry. It was beginning to bother me that I had no clue how the answer was what it was. Thank you both!