help on this gchem problem

[PreDental88]

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On one of the Kaplan exams I took, it says that this reaction will not proceed:

Zn + NaNO3 --> NR

The solutions manual was confusing and I was hoping to get help from anyone who knew why this reaction wouldn't proceed. Thanks!

 

[gigawatt]

The only reaction that could happen would be Zn displacing the Na:

Zn + NaNO3 --> Na + ZnNO3

Net ionic equation (NO3- is a spectator ion):

Zn + Na^+ --> Na + Zn^2+ (charges not balanced, but it's not relevant)

So we have Zn oxidized and Na reduced:

Na^+ + e- --> Na
E = -2.71

Zn --> Zn^2+ + 2e-
E = 0.76

The total E would be negative, meaning this reaction is non-spontaneous, and wouldn't happen as written.

Qualitatively, without all this, you know that Zn is not a strong enough reducing agent to reduce Na...hence, no reaction.

 

[Baylor2011]

Are you just supposed to know Zn isn't a strong enough reducing agent?

 

[toothfairy05]

Qualitatively, without all this, you know that Zn is not a strong enough reducing agent to reduce Na...hence, no reaction.

How do you judge whether something is a strong versus weak reducing agent/ oxidizing agent?

Thanks!

 

[wantVCUdental]

Are you just supposed to know Zn isn't a strong enough reducing agent?

look at the magnitude of E

 

[gigawatt]

How do you judge whether something is a strong versus weak reducing agent/ oxidizing agent?

Thanks!

In all likelihood, you won't have to on the DAT (at least not without being given E values, which makes it obvious).

For Na and Zn, in particular: solid Zn exists. You've probably used it in a gen chem lab before with HCl? Solid Na is so reactive it has to be stored under oil...it almost always occurs as Na+.

 

[toothfairy05]

In all likelihood, you won't have to on the DAT (at least not without being given E values, which makes it obvious).

For Na and Zn, in particular: solid Zn exists. You've probably used it in a gen chem lab before with HCl? Solid Na is so reactive it has to be stored under oil...it almost always occurs as Na+.

Thanks so much!