Calculate the pH of a buffer that is prepared by mixing 25.0 mL of 0.300 M methylamine (CH3NH2) and 0.405 g of methylammonium chloride with water to make 500.0 mL of solution.

The pH of the solution is 10.74

Explanation:

To calculate the number of moles, we use the equation:

Given mass of methylammonium chloride = 0.405 g

Molar mass of methylammonium chloride = 67.52 g/mol

Putting values in above equation, we get:

To calculate the number of moles for given molarity, we use the equation:

Molarity of methylamine solution = 0.300 M

Volume of solution = 25 mL = 0.025 L

Putting values in above equation, we get:

Total volume of the solution = [25 + 500] = 525 mL = 0.525 L   (Conversion factor: 1 L = 1000 mL)

To calculate the pOH of basic buffer, we use the equation given by Henderson Hasselbalch:  

We are given:  

= negative logarithm of base dissociation constant of methylamine = 3.36

pOH = ?

Putting values in above equation, we get:

To calculate the pH of the solution, we use the equation:

Hence, the pH of the solution is 10.74

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