[dan2000]

Hello,

So I'm trying to make a solution of same basicity as 10% sodium bicarbonate with potassium hydroxide.

But it's been so long, I can only vaguely remember making equilibrium constant and canceling out [H+][OH-]...and I think this was using concentrations (eg 0.1M) instead of pKa.

This is really basic stuff but can anyone explain this to me or link to a good site that does?

[Borek]

What is your definition of basicity? This is a pretty ambiguous term.

[dan2000]

I asked and forgot for a week, so i dont expect any replies, though will be very thankful.

I worded it wrong, I simply meant pH when i said basicity.

For examble, sodium bicarbonate pH at 0.1N is 8.4, but KOH's pH at 0.01N is 12

(from http://www.engineeringtoolbox.com/bases-ph-d_402.html)

Does this mean I have to dilute KOH to around 1x10^-6 N for it to have similar pH as sodium bicarbonate? And is there a general formula I can use (for those not measured)?

[Borek]

Theoretical calculations are pretty straightforward - from known pH calculate concentration of OH^- (pH+pOH=14), then assume concentration of OH^- is that of KOH. So yes - in theory diluting to more or less 10^-6 M is what you need.

In practice it won't work. This is a pretty diluted, alkaline solution, that will pretty fast absorb atmospheric CO₂ and pH will plummet down. No way of stabilizing the pH - other than using a buffer solution.

[dan2000]

I see. Thank you for your answer.

[dan2000]

Just really basic stuff.

If I had something like HF and titrated it with KOH, in the end it would consume exactly equal moles of them to make pH 7? So this doesnt take into account the acid/base strength?

Also, if it has 2 H+ (eg H2SO4), it would take 2 moles of KOH to neutralise 1 mole of H2SO4?

[Borek]

If I had something like HF and titrated it with KOH, in the end it would consume exactly equal moles of them to make pH 7?

Nope. While the stoichiometry of the reaction is as you expect (1:1 in the case of the HF/KOH, 2:1 in the case of H₂SO₄/KOH), pH at equivalence point is not 7.00.

Hint: at the equivalence point you have KF, salt of a strong base and a weak acid. What is its pH?

[dan2000]

well probably basic

then would it be as simple as i said if i use acid/base of similar magnitude?

how do i calculate this? is just from pKa using 7 as my zero point fine? (eg. pKa 3 acid with pKa 10 base)

[Borek]

http://www.titrations.info/titration-equivalence-point-calculation

http://www.titrations.info/acid-base-titration-equivalence-point-calculation