Question

What is the approximate fractional concentration of h2po4/hpo4 at pka 7.2 and ph=7.5?

Answer 1

pH = pKa + log [ HPO42-] / [H2PO4-]

Ka = 6.2 x 10^-8

pKa = 7.21

7.0 = 7.21 + log [HPO42-] / [HPO4-]

- 0.21 = log [ HPO42-] / [H2PO4-]

[ HPO42-] / [ H2PO4-] = 10^-0.21 = 0.617

[H2PO4-] / [HPO42-] = 1 / 0.617 = 1.62

Answer 2

Answer:

$1.62$

Explanation:

$pH = pKa + log [ HPO42-] / [H2PO4-]\\Ka = 6.2 x 10^{-8} } \\pKa = 7.217.0 = 7.21 + log [HPO42-] / [HPO4-]\\- 0.21 = log [ HPO42-] / [H2PO4-]\\[ HPO42-] / [ H2PO4-] = 10^{-0.21} = 0.617\\[H2PO4-] / [HPO42-] = 1 / 0.617 = 1.62$

Explanation about Concentration Fraction

• A concentration fraction denotes the particle size range used to calculate the concentration. For example, a concentration value of $C[80-200] = 1.6 E07$ particles/mL indicates that there is a particle concentration of $1.6 E07$ particles/mL within the size range of $80-200 nm.$
• It is critical to use a concentration fraction when comparing data. This ensures that the concentration values under consideration were calculated over the same size range.
• Data comparisons are frequently misinterpreted and false conclusions are drawn when a concentration fraction is not used. For a polydisperse sample, the minimum concentration fraction should not be set far below the measured distribution maximum.

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