[pop000]

1)BE the Equation (in the picture). I know that: CBr2HCOO- is more Stronger base than HCOO-.

CBr2HCOO- is gain proton more easy.

so the Question is: Which side will tend to balance?


2)what is the PH of Solution that it volume is 50 ml‏‏‏‏ and prepared by melting 0.012 gr Lithium hydroxide in Water.

thanks

[Unknown008]

1)

The Br being electronegative atoms will tend to pull the -ve charge in the ion towards itself. Hence, you can assume there is some degree of delocalisation of charge, and where there is delocalisation of charge, there is increased stability.

Now, this means that you will more likely end up with CBr2HCOO-. Where does the equilibrium lie?

2) First assumption is that all the LiOH dissociates into ions.

Then, you are dissolving this into water, and top to 50 mL

Find the number of moles of OH- in the solution (using the mass of LiOH used)

You can find pOH first.



Then use the relation:



to find the pH.

[DrBob1]

As a matter of fact, dibromoacetic acid is STRONGER than formic acid, hence its conjugate base is weaker. The reaction you wrote will lie to the right so as to produce the weaker acid and weaker base, the natural tendency of any acid/base reaction.
In Question 2 note that you DISSOLVE LiOH in water, not MELT it. Then, follow Unknown008's answer.

[pop000]

Well is will be correct if I will say: that the balance will tend to the right side because in this side there the more strong base CBr2HCOO- and it will gain in more proton so the balance will tend to right side. Proton is heavy proportionate to atoms weight.

Or maybe the answer is like this: we know that CBr2HCOO- is the strong base and in the right side we can see that there is no H+ and in the left side the HCOO- also don't have H+ but because CBr2HCOO- is more strong base than HCOO- (in the left side) so CBr2HCOO- will gain in proton so the balance will tend to the right side where is the CBr2HCOO-.

Do I correct? Thanks.

[Unknown008]

I usually try not to think in terms of strong acid or base because I would end up messing up with things :o

I prefer using delocalisation, stability, etc and as such didn't pay much attention to the 'stronger base' part.

For the second part, I didn't see the verb melt at all :p After reading those strange symbols, I jumped to LiOH in water :o

Thanks again for clearing things up!

[Unknown008]

well is will be correct if i will say: that the balance will tend to the right side because in this side there the more strong base CBr2HCOO- and it will gain in more proton so the balance will tend to right side. proton is heavy proportionate to atoms weight.

or maybe the answer is like this: we know that CBr2HCOO- is the strong base and in the right side we can see that there is no H+ and in the left side the HCOO- also don't have H+ but because CBr2HCOO- is more strong base than HCOO- (in the left side) so CBr2HCOO- will gain in proton so the balance will tend to the right side where is the CBr2HCOO-.

do i correct?. thanks.

I'm really sorry, but this is getting very confusing... may I ask in what language you are most at ease with? If it's French, I can manage.

But no, CHBr2COO- is a weak base as Dr. Bob just told you. As a weak base, it will not accept a proton to go to the left.

On the other hand, CHBr2COOH is a strong acid and will donate a proton to become CHBr2COO-

[pop000]

Well no I am not speak French my mother tongue is hebrew .
I will try to write it more clear :)

[Unknown008]

Oh... that's a tough one =/ I understand better now. Do try your best :)

[pop000]

U told that CHBr2COO- is the weak base but I speak about CBr2HCOO- and my teacher told is more strong base than HCOO- so maybe he mistake :)

[pop000]

Well what I am trying to say is if CBr2HCOO- is the strong base and we can find it in the left side so it ( CBr2HCOO- ) will accept proton from the material in the right side so the balance will move to the right side.

[Unknown008]

I would guess so.

Unfortunately, I don't have the information to confirm this... If you had the value (the acid dissociation constant of then we'll be sure which is the stronger acid between methanoic acid)

I worked with chloro-ethanoic acid, dichloro-ethanoic acid and trichloro ethanoic acid (CH2ClCOOH, CHCl2COOH and CCl3COOH) which are all more acidic than methanoic acid. But Br is a much weaker electronegative atom and has a slight chance of being more basic than HCOOH. But until I have the actual figures, I can't say for sure. I would guess that CHBr2COOH is more acidic otherwise.

[pop000]

Again you speak about CHBr2COO- and I about CBr2HCOO- there is different?

[Unknown008]

No, if CHBr2COO- is a strong base, then the equilibrium will lie on the left.

This is because the strong base would easily react with the proton from HCOOH to give the weak acid CHBr2COOH.

That is IF CHBr2COO- is the strong base.

[Unknown008]

No no, this is the same thing. I just have the habit to put all the H before an group coming afterwards. It's the same thing, don't worry.

[pop000]

OK I will ask my teacher who is more strong base is will be funny to show him his mistake if there really mistake.

And I will let you know if you are correct :)

[Unknown008]

Yes please :)

[DrBob1]

The pKa of bromoacetic acid is 2.69 while the pKa of formic acid is 3.75. The pKa of dibromoacetic acid will be even lower, meaning dibromoacetic acid is stronger. (I can't find the pKa of dibromoacetic acid.)
CBr2HCOOH and CHBr2COOH are the same compound - just go with the chemical name. Check with your teacher - dibromoacetate is a weaker base than is formate. Perhaps you misunderstood your teacher.

[pop000]

OK I asked and Because it is holiday he send me email to keep follow after the instructions.

Mean CBr2HCOO- is the strong base than HCOO- so if we will follow after this instructions so where the balance will tend? Which side?

Thank to both of you really.

[DrBob1]

If we grant the premise that bromoacetate is the stronger base, the reaction lies to the left as you have writtten it. But the premise is wrong!
This is like saying that if 2 + 2 = 5 then, yes, 2 + 3 = 6. LOGICALLY correct, chemically and mathematically wrong!

[pop000]

Yes you are correct 100% tell me if the pka become more is mean that the acid is more strong?
Thanks.