One GC question from old DAT

[vDDmaniaC]

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Hi,
I really dont' know how to solve this question so I ask here.
The question is

In an aqueous solution the following equilibrium reactions are present:

Ag(NH3)2^+ <=> Ag+ + 2NH3
NH3 + H2O <=> NH4+ + OH-

If the soluble salt AgNO3 is added to the solution, the following changes in concentration take place

1. NH3, NH4+ and OH- decrease
2. NH3 increases; NH4+ and OH- decrease
3. NH4+ increase; NH3 and OH- decrease
4. NH4+ and OH- increase; NH3 decrease
5. NH3 and OH- increase; NH4+ decrease

Please help me out of this question!
THanks,
🙄😉

 

[shoombol tallah]

is the answer 1 ?

 

[yakuza]

Is it 4?

 

[ldm0208]

Is it 4?

I think it's 4 too by the common ion effect

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not anymore, I think it's 1...what's the anwer!!??

 

[niktacal82]

I think the answer is 2; AgNO3 completely dissociates to Ag+ and NO3-; therefore the first eq shifts to the left,Ag(NH3)2^+ <=> Ag+ + 2NH3(toward producing Ag(NH3)2 to consume all the extra Ag+ in the solution). But NH3 decreases cuz of that, so the second eq NH3 + H2O <=> NH4+ + OH- shifts to the left to make more NH3. So we end up with more NH3 but less NH4+ and OH-.
I am not sure though😎

 

[yakuza]

I think the answer is 2; AgNO3 completely dissociates to Ag+ and NO3-; therefore the first eq shifts to the left,Ag(NH3)2^+ <=> Ag+ + 2NH3(toward producing Ag(NH3)2 to consume all the extra Ag+ in the solution). But NH3 decreases cuz of that, so the second eq NH3 + H2O <=> NH4+ + OH- shifts to the left to make more NH3. So we end up with more NH3 but less NH4+ and OH-.
I am not sure though😎

That makes more sense. I was thinking in the 1st reaction NH3 decreases shifting, so it simultaneously decreases in the 2nd one also, but making it shift right(using NH3). But if you think about it in terms of the 2nd one coming in effect AFTER the first 1 like you said, it sounds a lot better

I think its 2 now lol

 

[ldm0208]

I think the answer is 2; AgNO3 completely dissociates to Ag+ and NO3-; therefore the first eq shifts to the left,Ag(NH3)2^+ <=> Ag+ + 2NH3(toward producing Ag(NH3)2 to consume all the extra Ag+ in the solution). But NH3 decreases cuz of that, so the second eq NH3 + H2O <=> NH4+ + OH- shifts to the left to make more NH3. So we end up with more NH3 but less NH4+ and OH-.
I am not sure though😎

Yeah you changed my mind. But now I am debating between 1 and 2. From your explanation, you end up with more NH3, I think that NH3 shifts the top rxn to the left even more. So, I now think the answer should be 1..NOT sure this is right but it's a good question I think because I got tricked..😱

 

[shoombol tallah]

yeah but NH3 is the intermediate in this reaction. It is produced and then consumed. So if the first reaction was inhibited by the common ion effect then no NH3 would be produced to act as the intermediate (reactant) for the second reaction. Thats my reasoning for choosing 1, where is this guy btw doesnt he know people are waiting 🙂

 

[niktacal82]

IDmo208 I know what you mean...lol..now i am thinking more..
Also , to shoombooltala: I think eq shifts (like more to the left) not become an irreversible rxn and having no more NH3..we would have NH3 in the solution but decreases..you know..

 

[shoombol tallah]

lol yeah sorry thats what i meant the equilibrium shifts to the left and decreases NH3 there still would be some present but less than there were before AgNO3 was added. But I think that still answers the question, the overall result is a decrease in NH3 which in turn decreases NH4 and OH .

 

[PooyaH]

Since more Ag+ will be dissociating in the solution, more NH3 is needed; thus, "NH4+ + OH-" part of the second reaction would want to shift to the left to make more NH3! (increase NH3)
Shoombol jan, NH3 is in fact an intermediate but it is still needed to push the reaction forward and eventually make NH4+ and OH-.

So choice 2 all the way! 😉 Please please please say it's 2! 😀

 

[niktacal82]

😀ok! hopefully i am not confusing you Idm0208..but when NH3 decreases from first eq( lets say from 0.5 M goes to 0.2 M), and make the second one shift to the left, it's not like ending up with 2 M NH3( cuz we 1st decreased it)..so we would end up with ~0.3M ..so this wouldn't put alot of stress on the whole system to go from top and use the excess NH3..

god hopefully i am right !

 

[ldm0208]

😀ok! hopefully i am not confusing you Idm0208..but when NH3 decreases from first eq( lets say from 0.5 M goes to 0.2 M), and make the second one shift to the left, it's not like ending up with 2 M NH3( cuz we 1st decreased it)..so we would end up with ~0.3M ..so this wouldn't put alot of stress on the whole system to go from top and use the excess NH3..

Ok..lil confusing. If I understood what you said right, I should still think the anwer is 1? 😎 Well I just want the answer now.😀 But the guy is not on..man.....

 

[yakuza]

LOL! man wheres the OP?? I need the answer so I can stop looking at it and start studying

 

[harrygt]

I agree with "Golden Shomboll". The first reaction will shift to left, inducing the second reaction to shift to left as well. Adding Ag+ decreases [NH3], and the shift of the second reaction only relieves some of this decrease in [NH3]. However, the shift of the second reaction to left will not increase the concentration of NH3.

 

[yakuza]

I agree with "Golden Shomboll". The first reaction will shift to left, inducing the second reaction to shift to left as well. Adding Ag+ decreases [NH3], and the shift of the second reaction only relieves some of this decrease in [NH3]. However, the shift of the second reaction to left will not increase the concentration of NH3.

But regardless, NH3 will increase, and then just react again with Ag+. So will that count as increase in NH3

 

[vDDmaniaC]

Sorry guys.....
took so long to come back.
the answer is 1. But I am still not sure why it is the answer. Can any one simplify why the answer is 1?

 

[harrygt]

Here is an example in order to better understand this question:
A + B <---> C + D At equilibrium.
Let's say we have 30 moles of C in the container. We take 10 moles of C out, leaving us with 20 moles of C in the container. The equilibrium will shift to right in order to relieve this big change. We will end up with let's say 25 moles of C, but obviously we are not going to get more than the initial amount [30 moles].

The point is that adding Ag+ will decrease the [NH3], and the shifting of the second reaction to the left will ONLY RELIEVE this decrease in [NH3]. It won't end up giving you more NH3.

 

[ldm0208]

The point is that adding Ag+ will decrease the [NH3], and the shifting of the second reaction to the left will ONLY RELIEVE this decrease in [NH3]. It won't end up giving you more NH3.

There you go! The answer is 1! I got tricked first but I figured it out next...🙂 Thank you guys! It was a good question with an active debate. 👍

 

[yakuza]

Here is an example in order to better understand this question:
A + B <---> C + D At equilibrium.
Let's say we have 30 moles of C in the container. We take 10 moles of C out, leaving us with 20 moles of C in the container. The equilibrium will shift to right in order to relieve this big change. We will end up with let's say 25 moles of C, but obviously we are not going to get more than the initial amount [30 moles].

The point is that adding Ag+ will decrease the [NH3], and the shifting of the second reaction to the left will ONLY RELIEVE this decrease in [NH3]. It won't end up giving you more NH3.

I don't get why it only relieves it. Where did you read that it doesn't fully go back to normal?

 

[harrygt]

I don't get why it only relieves it. Where did you read that it doesn't fully go back to normal?

Le Chatelier's Principle

If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or total pressure, then the equilibrium shifts to partially counter-act the imposed change.

Reference: http://en.wikipedia.org/wiki/Le_Chatelier's_principle

 

[yakuza]

[/color]

Le Chatelier's Principle

If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or total pressure, then the equilibrium shifts to partially counter-act the imposed change.

Reference: http://en.wikipedia.org/wiki/Le_Chatelier's_principle

Oh wow, I really didn't know its only partial. Thanks

 

[shoombol tallah]

hey harry chetori thanks for the golden shombol shout out. The shombol loves you too man...but not in that way 🙂 and pooya thats what happens when a perspolisi tries to correct a taji 🙂 ha ha just kidding bro.

 

[ksksks]

aite the simple reason why its 1

Soluble salt AgNO3 will dissociate into Ag and NO3
NO3 is not even needed because none of these reactions involve NO3. So Ag+ is increased.

In the first reaction, Ag+ increase will shift reaction towards the reactants, reducing NH3.

Because NH3 is now reduced, it favours the reactant side in reaction 2, increasing NH4 and OH-

Hope that clears things.

In an aqueous solution the following equilibrium reactions are present:

Ag(NH3)2^+ <=> Ag+ + 2NH3
NH3 + H2O <=> NH4+ + OH-

If the soluble salt AgNO3 is added to the solution, the following changes in concentration take place

1. NH3, NH4+ and OH- decrease
2. NH3 increases; NH4+ and OH- decrease
3. NH4+ increase; NH3 and OH- decrease
4. NH4+ and OH- increase; NH3 decrease
5. NH3 and OH- increase; NH4+ decrease

 

[harrygt]

aite the simple reason why its 1

Soluble salt AgNO3 will dissociate into Ag and NO3
NO3 is not even needed because none of these reactions involve NO3. So Ag+ is increased.

In the first reaction, Ag+ increase will shift reaction towards the reactants, reducing NH3.

Because NH3 is now reduced, it favours the reactant side in reaction 2, increasing NH4 and OH-????????????????

Hope that clears things. NO it does not!

In an aqueous solution the following equilibrium reactions are present:

Ag(NH3)2^+ <=> Ag+ + 2NH3
NH3 + H2O <=> NH4+ + OH-

If the soluble salt AgNO3 is added to the solution, the following changes in concentration take place

1. NH3, NH4+ and OH- decrease
2. NH3 increases; NH4+ and OH- decrease
3. NH4+ increase; NH3 and OH- decrease
4. NH4+ and OH- increase; NH3 decrease
5. NH3 and OH- increase; NH4+ decrease

Boy, everything was clarified, and you just messed it up again.

 

[harrygt]

hey harry chetori thanks for the golden shombol shout out. The shombol loves you too man...but not in that way 🙂 and pooya thats what happens when a perspolisi tries to correct a taji 🙂 ha ha just kidding bro.

hahaha, lol