Lesson 7 Buffer Solutions CLASSNOTES
Buffer Solutions
w A buffer solution (or just buffer) is a solution that resist changes in pH
when (strong) acids or (strong) bases are added to them.
w A buffer is made up of:
1. a weak acid or weak base and
2. its salt (i.e. conjugate base or conjugate acid, respectively)
w The two components are mixed to produce approximately equal molar
concentrations of the conjugate acid­base pair.
w Buffer solutions have two important characteristics:
1. the pH of the solution
2. its buffer capacity: the amount of acid or base that can be added before
considerable change occurs to pH
e.g. acetic acid – sodium acetate buffer solution
i.e. acid/salt
or
CH3COOH/CH3COONa
∴ CH3COOH (aq) ⇌
acid/conjugate base
CH3COOH/CH3COO–
H+ (aq) +
CH3COO– (aq)
Example 1:Which of the following solutions are buffer systems? Explain your answer.
a) H3PO4/KH2PO4
b) HClO4/NaClO4
c) C5H5N/C5H5NCl
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Lesson 7 Buffer Solutions CLASSNOTES
In general:
HA (aq) +
H2O (l) ⇌ H3O (aq) + A– (aq)
Example 2:
a) Calculate the pH of buffer system containing 1.0 mol/L CH3COOH (aq)
and 1.0 mol/L CH3COONa (aq) .
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Lesson 7 Buffer Solutions CLASSNOTES
b) What is the pH of the buffer system after the addition of 0.10 mole of gaseous HCl to 1 L of the
solution? (Assume volume of the solution does not change when the HCl is added).
Example 3:
If 1 L of a 0.1 mol/L CH3COOH (aq) is prepared and 5.0 g of sodium acetate, NaCH3COO(s), is added
to the acid, what will be the pH of the buffer system? Ka (CH3COOH(aq)) is 1.8 x 10–5.
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Lesson 7 Buffer Solutions CLASSNOTES
Example 4:
A buffer is prepared by adding 5.0 g of NH4NO3 (s) to 1.0 L of a 0.1 mol/L NH3 solution.
What is the pH of the buffer?
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