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Chemical equations- the Ka and Henderson Hasselbalch equation

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Please help, I'm really stuck on the following:-

A weak acid has a PKa of 7.713. Calculate the pH of a solution in which the ratio of the concentrations of undissociated acid to acid anion ([HA]/[A-]) equals 8.441

also

Calculate the PKa of a weak acid given the information that a 0.652 M solution has a pH of 2.882

and

Calculate the pH of a 0.24 M solution made from a weak acid whose PKa is 4.271

Hope you can help or at least point me in the right direction.

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See Also This Related BrainMass Solution

Acid - Base Reactions Henderson-Hasselbalch Equation

Please show all work.

Do NOT use the Henderson-Hasselbalch equation in solving any of these questions.

1. Ksp = 2 x 10^-19 for LaF3 in water at 25 degrees celcius. How many grams of LaF3 are present in 500 mL of saturated LaF3(aq) at 25 degrees celcius ? The atomic weight of La is 139.

2. Find [H+] in 0.25 M NaC2H3O2 (aq) at 25 degrees celcius given that Ka = 1.8 x 10^-5 for HC2H3O2 (aq) at 25 degrees celcius. You MUST begin by writing the chemical reaction that is at equilibrium.

3. Find [H+] in a solution prepared by dissolving 1.50 g of Ca(OH)2 in 600 mL of water and diluting the solution to a final volume of 800 mL.

4. Find the pH when 45.0 mL of 0.250 M NaOH (aq) is added to 35.0 mL of 0.200M HCl (aq).

5. Find [H+] in a solution prepared by adding 0.40 moles of NaCN to 500 mL of a 0.25M HCN(aq) solution. Assume that there is no volume change when the NaCN is added. For HCN(aq), Ka = 4.9 x 10^-10.

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