Question

Phosphate-buffered saline (PBS) is one of the commonly used buffers to maintain the pH value during the purification of biology related samples. Below are all the components for PBS buffer: NaCl, KCl, Na₂HPO₄ and KH₂PO₄.

A. Please identify the acidic and basic component of the buffer. (Hint: acidic and basic components should be a conjugate acid-base pair.)

B. Please write the chemical equation that will happen when additional HCl is added into the buffer. (Hint: acids like to react with bases.)

C. Please write the chemical equation that will happen when additional NaOH is added into the buffer. (Hint: bases like to react with acids.)

D.What is the effective buffer range? (K_a for H₂PO₄^- is 6.3 x 10 ^-8)

E. In order for cells to properly propagate, pH has to be maintained around 7.40. What is the ratio between the acidic and basic component when pH is measured to be 7.40?

Answer 1

A.

is the acidic component of buffer. is the basic component of the buffer.

The conjugate acid base pair is and .

B.

HCl is added to the buffer.

HCl is an acid. It reacts with base .

C.

NaOH is added to the buffer.

NaOH is base. it reacts with acid .

D.

The effective buffer range is about 1 pH unit on either side of the pKa of the conjugate acid.

The effective buffer range is about 6.20 to 8.20.

E.

The ratio between acidic and basic components is