Question

You are given 100.0 mL of a buffer that is 0.50 M in KH₂PO₄ and 0.40 M in KH₂PO₄. Potassium ions are spectator ions in solution and do not participate in the acid-base reaction.

a)The weak acid is _________
b)The conjugate base is ________
Recall that in solution, the number of moles of solute = Volume (L) x Molarity (mol/L). Pay attention to units!
Calculate the number of moles of the weak acid in this buffer.
Calculate the number of moles of the conjugate base in this buffer.

Answer 1

a) The weak acid is KH₂PO₄ and b) The conjugate base is K₂HPO₄. The number of moles of the weak acid in the buffer is 0.05 mol and the number of moles of the conjugate base is 0.04 mol.

Step-by-step explanation:

a) The weak acid is KH₂PO₄.
b) The conjugate base is K₂HPO₄.

To calculate the number of moles of the weak acid in the buffer, we use the formula:
Number of moles = Volume (L) x Molarity (mol/L)

Given:
Volume = 100.0 mL = 0.1 L
Molarity = 0.50 M

Number of moles of weak acid = 0.1 L x 0.50 mol/L = 0.05 mol

To calculate the number of moles of the conjugate base in the buffer, we use the same formula:
Number of moles = Volume (L) x Molarity (mol/L)

Given:
Volume = 100.0 mL = 0.1 L
Molarity = 0.40 M

Number of moles of conjugate base = 0.1 L x 0.40 mol/L = 0.04 mol