  ) If 5.0 mL of 0.100 M NaOH is added to 100.0 mL of a 0.0500M phosphate buffer solution at pH 7.2, what is the resultant pH of the solution?

Question

) If 5.0 mL of 0.100 M NaOH is added to 100.0 mL of a 0.0500M phosphate buffer solution at pH 7.2, what is the resultant pH of the solution?

Step 1

A solution which resists the change in pH when a small amount of acid or base is added to it,  is known as a buffer solution. The behaviour of a buffer is described by the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation for a mixture of weak acids and its salts with a strong base is shown.

Step 2

In order to calculate the resultant pH of the solution, first calculate the number of moles of NaOH and the phosphate buffer before the addition of NaOH.

The product of volume and concentration gives the number of moles which is expressed by equation (1)

For 5.0 mL of 0.100M NaOH, the number of moles is calculated using equation (1) as shown in equation (2)

For 100.0 mL of 0.0500M phosphate buffer, the number of moles is calculated using equation (1) as shown in equation (3)

Step 3

Now, calculate the number of moles of H2PO4- and HPO42- that are present after the addition of NaOH.

The reaction between phosphate buffer and NaOH is represented by equation (4).

Initially, 5 mmol of phosphate buffer is present. After the addition of 0.5 mmol of NaOH, 4.5 mmol of H2PO4- and...

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