Question

A formic acid buffer containing 0.50 M HCOOH and 0.50 M HCOONa has a pH of 3.77.

What will the pH be after 0.010 mol of NaOH has been added to 100.0 mL of the buffer? (Assume the addition cause negligible volume change.)

Answer 1

Concepts and reason

The concept used here is based on the dissociation constant of an acid is used for the determination of the strength of an acid. Higher the value of dissociation constant, higher will be acid strength and vice versa.

The Henderson-Hasselbalch equation is used for the determination of the corresponding to the buffer solution. A buffer solution is basically composed of an acid and its corresponding conjugate base or vice versa.

Fundamentals

The molarity of a solution is given as shown below.

…… (1)

Here, is a number of moles of solute, is the volume of solution in liters.

The Henderson-Hasselbalch equation is given as shown below.

…… (2)

Here, is the negative logarithm of the dissociation constant, is the concentration of salt and is the concentration of acid.

To calculate the moles of , substitute the value of as , as in the equation (1)

To calculate the moles of , substitute the value of as , as in the equation (1)

The Henderson-Hasselbalch equation for the solution can be written as shown below using equation (2).

Now, substitute the value of as , as and as in the above equation

The chemical equation after the addition of sodium hydroxide can be written as shown below.

To calculate the concentration of substitute as and as in the equation (1).

To calculate the concentration of substitute as and as in the equation (1).

The Henderson-Hasselbalch equation for the solution can be written as shown below using equation (2).

Now, substitute the value of as , as and as in the above equation.

The of the solution after the addition of sodium hydroxide is .

Ans:

The of the solution after the addition of sodium hydroxide is .