# A student needs to prepare a buffer solution with a pH of 4.60. Assuming a pK a of 4.12, how many mL of 0.1 M B minus would need to be added to 20.0 mL of 0.1 M HB prepare this buffer? Please include a proper (abbreviated) unit.HINT : Use pH = pK a + log ([B minus]/[HB]) or, if concentrations are the same, pH = pK a + log (Volume of B minus / Volume of HB)

Question

A student needs to prepare a buffer solution with a pH of 4.60. Assuming a pK a of 4.12, how many mL of 0.1 M B minus would need to be added to 20.0 mL of 0.1 M HB prepare this buffer? Please include a proper (abbreviated) unit.
HINT : Use pH = pK a + log ([B minus]/[HB]) or, if concentrations are the same,
pH = pK a + log (Volume of B minus / Volume of HB)

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Step 1

A solution which resists 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, which is shown in equation (1).

Step 2

The concentrations of the conjugate base (B-) and the acid (HB) are same, that is 0.1 M.

Thus, the Henderson Hasselbalch equation for the given buffer is shown in equation (2).

Step 3

Consider the volume of the conjugate base (B-) to be V mL.

Substitute, 4.12 for pKa, 4.60 for pH, V mL for volume...

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