just took a chemistry test...

[theMan]

So, the question is,

What is the effect of adding a small amount of CsOH to a .1M HCN solution?

and it was multiple choice.

i cannot remember the exact choices, but they had to do with increasing/decreasing Ka, changing the concentration of CN- or the concentration of HCN. or, no change.

not sure.

 

[TecHNooB]

Hooray!

 

[theMan]

Originally posted by: TecHNooB
Hooray!

yeah, ok, i pressed enter instead of tab when i went down to the next field, is that really so much of a crime???

 

[Bitek]

Well you would be adding a base to an acid, so you would increase the pH and create a salt.

 

[theMan]

yeah, but that wasnt a choice. let me think...

i think the choices were:

a) it would increase [HCN]
b) Ka of HCN would decrease (or increase, not sure)
c) [CN-] would increase
d) no change
e) [CN-] would increase

i am pretty sure what the choices were, but not totally, it is something along those lines.

 

[Kevin1211]

Originally posted by: Hafen
Well you would be adding a base to an acid, so you would increase the pH and create a salt.

salt + h20

 

[Brainonska511]

Ka would remain the same for HCn since it is a fixed value for each compound.

C and E are the same choices. I would go with [CN-] would increase since HCn is a weak acid and adding the OH- into solution would push equilibrium and cause the HCn to dissociate more as the salt is formed.

 

[Toastedlightly]

the CN- ion would decrease (as I asssume CsCN is non-soluable

 

[Serp86]

dude - its just one question in a test

heck, im getting a degree in chemistry and can hardly answer that - havent done dissosciation constants in a long time, and your choices are too vague. So unless youre typing this during the test, give it a rest, will you 🙂

 

[rainglue]

I agree with Brainonska511. I believe that [CN-] would increase. HCN is a weak acid, and CsOH is a strong base. Prior to the addition of the base, HCN is in equilibrium:
H+ + CN- <=> HCN.

When CsOH is added, H+ and OH- will react to completion (with OH- being the limiting reagent). As the H+ combines with OH- to form water, the equilibrium will shift to the left, forming more CN-.

Ka will not change unless temperature changes. And CsCN is a soluble salt since Cs is a Group I metal.

 

[Toastedlightly]

Originally posted by: rainglue
I agree with Brainonska511. I believe that [CN-] would increase. HCN is a weak acid, and CsOH is a strong base. Prior to the addition of the base, HCN is in equilibrium:
H+ + CN- <=> HCN.

When CsOH is added, H+ and OH- will react to completion (with OH- being the limiting reagent). As the H+ combines with OH- to form water, the equilibrium will shift to the left, forming more CN-.

Ka will not change unless temperature changes. And CsCN is a soluble salt since Cs is a Group I metal.

I couldn't remember those damn solubility rules. This seems to be correct.

 

[Fenixgoon]

Originally posted by: Kevin1211

Originally posted by: Hafen
Well you would be adding a base to an acid, so you would increase the pH and create a salt.

salt + h20

CsCN will *should* be soluble in water... so it's just H2O 😛

 

[theMan]

Originally posted by: rainglue
I agree with Brainonska511. I believe that [CN-] would increase. HCN is a weak acid, and CsOH is a strong base. Prior to the addition of the base, HCN is in equilibrium:
H+ + CN- <=> HCN.

When CsOH is added, H+ and OH- will react to completion (with OH- being the limiting reagent). As the H+ combines with OH- to form water, the equilibrium will shift to the left, forming more CN-.

Ka will not change unless temperature changes. And CsCN is a soluble salt since Cs is a Group I metal.

yeah, that must be right. i really cannot remember which answer i decided upon. anyway just another quick question...

Phosphine acts as a Lewis base right?

I really needed to get a good score on this, and i am a bit nervous... :roll: