# Chemistry

posted by .

Hi,
I am having trouble with two questions.

Find the pH of the following aqueous solutions prepared by adding:

a) 20mL 0.12M HCl to 10mL 0.16M CH3COOH + 20mL 0.20 KOH.

b) 10mL 5.0x10^-7 M HCl to 90mL H2O

For a), I thought it was a buffer solution so what I tried to do was find the initial moles and add or subtract the moles of HCl (as it reacts with the conjugate base to create more conjugate acid). But then I realised that CH3COOH and KOH were not conjugate pairs. So what do I do?

For b), I tried using M1V2 = M2V2 but the sheet said that "the trivial answer to this is not correct". So how do I do this ?

• Chemistry -

For a, neutralize HCl with KOH (and there should be KOH left over) and use the excess KOH to neutralize CH3COOH. I think the mmoles left over from the first neutralization will be just the amount to neutralize the CH3COOH. So what you will have in the solutin is KCl (which doesn't affect the pH), H2O from both neutralizations (which is neutral), and CH3COOK (potassium acetate). The acetate ion )a base) is hydrolyzed like so
CH3COO^- + HOH ==> CH3COOH + OH^-

Kb = (K2/Ka) = (CH3COOH)(OH^-)/(CH3COOK).
Set up an ICE chart and substitute into the Kb equation and solve for OH^-, convert to pOH, then to pH. For CH3COOK, that will be the moles formed from the appropriate neutralization divided by the volume of ALL of the solutions.

For b, the trivial answer is not correct because the concn of the HCl given is so SMALL. Remember that the concn of H and OH in water is 1 x 10^-7 M. We usually neglect that when working with solutions BUT when the added soln is about the same, it is no longer negligible. So the total H^+ will be the sum of H^+ from HCl + H^+ from the H2O (which by the way will not be 1 x 10^-7 M).

• Chemistry -

Thanks,

But for the second one.
What will [H+] be if its not 1x10^-7 ?

## Similar Questions

1. ### Science - Chemistry

Having some trouble elaborating on a answer/conclusion for my investigation report. Why is it, that if we add more 2M HCl to 1gram of carbonate(crushed shells), the reaction takes longer to stop?
2. ### college chemistry

How do you calculate the pH difference when the following substances are added to a buffer.(all of the solutions are at .10M conc.) The buffer: 50mL NH3 + 50mL NH4NO3 1) 10mL buffer + 6mL water 2)10mL buffer + 5mL water +1mL HCl 3)10mL …
3. ### college chemistry

How do you calculate the pH when the following substances are added to a buffer.(all of the solutions are at .10M conc.) The buffer: 50mL NH3 + 50mL NH4NO3 1) 10mL buffer + 6mL water 2)10mL buffer + 5mL water +1mL HCl 3)10mL buffer …
4. ### chemistry

How do you calculate the pH when the following substances are added to a buffer.(all of the solutions are at .10M conc.) The buffer: 50mL NH3 + 50mL NH4NO3 1) 10mL buffer + 6mL water 2)10mL buffer + 5mL water +1mL HCl 3)10mL buffer …
5. ### chemistry lab titration

10.0 mL aliquot of 0.100M Na3AsO4 is titrated with 0.100M HCl. pKa1=2.25 pKa2=6.77 pKa3=11.60 Sketch the titration graph by calculating the pH at 0mL, 5mL, 10mL, 15mL, 20mL, 25mL, 30mL, 40mL of HCl.
6. ### chemistry

can u pls identify which has the greater activation energy. A cube of Fe reacting with 20mL, 1.0mol/L HCl or powdered Fe, having a the same mass, reacting with 20mL,1.0 mol/L HCl
7. ### chemistry

what is ph during titration of 10.00ml of 0.1000m triethylamine, ch3ch2)3n (kb=2.3x10^-, with 0.1000m HCL solution after addition of titrant (HCL) 1, 0ml, 5ml,10ml, 20ml,30ml
8. ### chemistry

indicate the concentration of each ion presentin the solution formed by mixing 20mL of .1M HCL and 10mL of .22 M HCL
9. ### Chemistry 2

For the reaction: 2A + 3B <--> 4C Kinetic data are as follows A B time needed 10mL 5mL 720 seconds 20mL 5mL 180 seconds 20mL 10mL 90 seconds 30mL 20mL ?
10. ### Chemistry

20ml H2SO4 and 10ml HCl can be neutralized by 20ml NaOH (0.1M) separately.Calculate the pH of the acids?

More Similar Questions