Question

Now assume you wish to make a buffer at the same pH, using the same substances, but want the total phosphate molarity ([HPO₄₂−]+[H₂PO₄−]) to equal 0.25 M. What concentration of the KH₂PO₄would be required?

Express your answer to two significant figures.

Answer 1

The concentration of KH₂PO₄ required to make a buffer with a total phosphate molarity of 0.25 M is also 0.25 M.

Step-by-step explanation:

To calculate the concentration of KH₂PO₄ required to make a buffer with a total phosphate molarity of 0.25 M, we need to consider the molar ratios of the substances involved. The balanced equation for the reaction between phosphoric acid (H₃PO₄) and KH₂PO₄ is:

H₃PO₄ + KH₂PO₄ → K₂HPO₄ + H₂O

From the equation, we can see that 1 mole of H₃PO₄ reacts with 1 mole of KH₂PO₄ to form 1 mole of K₂HPO₄. This means that the concentrations of H₃PO₄ and KH₂PO₄ are equal in the buffer solution. Therefore, the required concentration of KH₂PO₄ is 0.25 M.