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Multiple Choice
If you have 500.0 mL of a 0.10 M solution of HClO, what mass of NaClO (molar mass = 74.44 g/mol) do you need to add to make a buffer with a pH of 7.5?
A
7.44 g
B
3.72 g
C
1.86 g
D
0.93 g
Verified step by step guidance
1
First, understand that you are creating a buffer solution using HClO and NaClO. A buffer solution resists changes in pH when small amounts of acid or base are added.
Use the Henderson-Hasselbalch equation to find the ratio of the concentrations of the conjugate base (ClO⁻) and the weak acid (HClO). The equation is:
Determine the of HClO. You can find this value in a chemistry reference table. For HClO, is approximately 7.5.
Since the desired pH is 7.5, set up the equation: . This simplifies to , meaning .
Calculate the mass of NaClO needed. Since , the concentration of ClO⁻ should be 0.10 M in 500.0 mL. Use the formula: to find the mass of NaClO needed.