Acids and Bases: Buffer Action - Calculating pH of Buffers

Question 1

What equation is used to calculate [H+] so you can calculate the pH of a buffer solution?

Answer 1

• Ka = [H+][A-] / [HA]

Question 2

What are the different ways an acidic buffer can be made?

Answer 2

• Adding the salt to the weak acid

- Adding strong base to an excess of the weak acid

Question 3

How do you calculate the pH of an acidic buffer solution after addition of the salt when given:

• Ka for weak acid
• the mass and Mr of the salt of weak acid
• the concentration and volume of weak acid?

Answer 3

• Write expression for Ka
• Calculate number of moles of salt
• Calculate number of moles of weak acid
• Calculate [H+] using [H+] = Ka x (nHA / nA-)
• Calculate pH

Question 4

How do you calculate pH of a buffer solution after addition of an acid when given:

• Ka for original buffer acid (weak acid)
• initial moles for salt ions and original buffer acid
• concentration and volume of acid added?

Answer 4

• Write expression for Ka
• Calculate number of moles of added acid to calculate moles of H+ added
• Use ICE table to find moles of salt and original buffer acid
• Calculate new [H+] using [H+] = Ka x (nHA / nA-)
• Calculate pH

Question 5

How do you calculate the pH of a buffer solution after addition of a base when given:

• Ka for original buffer acid (weak acid)
• initial moles of original buffer acid and its salt
• concentration and volume of base added?

Answer 5

• Write expression for Ka
• Calculate number of moles of base added
• Use ICE table to find moles of salt and original buffer acid
• Calculate [H+] using [H+] = Ka (nHA / nA-)
• Calculate pH