Calculating the pH after dilution

Hi,

Quick Question:

For AQA Chemistry, A2, Module 4, do we need to know how to calculate the pH after dilution? I know we need to do buffer calcs, and pH after dilution is similar, but it isn't mentioned anywhere in that section of the specification. My teacher doesn't really know what to teach, mainly because she's a noob, so I would appreciate some replies from people with better teachers.

TY.

Reply 1

Stoney12345

Why is this in the medicine forum?

Reply 2

Demon_AS

13

I'm guessing because the OP knows most of us have done chemistry lol.

OP: Post this in the Academic Help forum, under A level Chemistry.

OP

Lol

OP

It moved for me, how good is that :smile:

Reply 5

Gangsta Boogie

OP

7

Now could someone answer please?

Thanks.

Reply 6

*Princess*

Gangsta Boogie

Hi,

Quick Question:

For AQA Chemistry, A2, Module 4, do we need to know how to calculate the pH after dilution? I know we need to do buffer calcs, and pH after dilution is similar, but it isn't mentioned anywhere in that section of the specification. My teacher doesn't really know what to teach, mainly because she's a noob, so I would appreciate some replies from people with better teachers.

TY.

Yes we do I think
I remember doing it vaguley

Reply 7

Gangsta Boogie

OP

7

OK... Thanks, but does anyone know for sure? Aah well, I'll just learn it anyway, it's not to long.

Reply 8

trektor

7

Gangsta Boogie

OK... Thanks, but does anyone know for sure? Aah well, I'll just learn it anyway, it's not to long.

the chemistry mock i did ages ago (june 2008) that i have in front of me now

question 1d (i)

says calculate the pH of the solution formed when 100cm3 of pure water is added to this 100cm3 buffer solution

that shows you need to.

*at first i just gave the same pH that the buffer solution originally started with as i had no idea and it turned out to be right*

*i then figured out using the rest of the information you can use:

ka*[HA]/[A-] = [H+]

that you can get a value for [H+]

i then -log10'd it and got the same pH that the original solution started with*

by dilution i think that is what you meant or do you mean dilution as in addition of an acid or alkali (if so then the above bit is not so relavant) but you will need to be able to calc pH after addition of acid or alkali (is that what you mean by buffer calc?

I can post something about addition of acid or alkali such as the bit where you add and take it away from the acid/alkali moles depending on the question

hope this helps

Reply 9

Tech

12

aha!
they asked me this in my oxford interview and I literally didn't have a *clue* ! kinda harsh that it's not something i've done in chem =\

Reply 10

Revd. Mike

17

You could well get a question like "Calculate the pH of a solution formed by the addition of 10cm^3 of 0.4M H2SO4 to 50cm^3 of water" or "a student added 3cm^3 of monoprotic strong acid to a flask, and made a solution up volumetrically to 100cm^3. Calculate the pH"

Calculating the pH after dilution

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