Calculate Ka for the weak acid HA, given that a buffer solution that is (5.000x1

Question

Calculate Ka for the weak acid HA, given that a buffer solution that is (5.000x10^-1)M HA and (5.000x10^-1)M NaA and has a pH of (5.1x10^0).

Calculate the pH of a buffer solution that is 0.25M in HC2H3O2 and 0.40M NaC2H3O2.

Assume you have a 1L of a buffer solution that is made from 0.4M of both HC2H3O2 and NaC2H3O2 and a 1 L of a second buffer solution that is made from 0.1M HC2H3O2 and 0.4M NaC2H3O2. To which buffer solution could you add 2L of 0.1M NaOH solution and cause the smaller pH change? Briefly explain.

Explanation / Answer

1)   pH = pKa + log [NaA/HA]

       5.1 = pKa + log[5.000x10^-1]/[5.000x10^-1]

pKa = 5.1

Ka = 7.94 x 10^-6

2)

pH = pKa + log [ NaC2H3O2 / HC2H3O2]

pH = 4.74 + log (0.40 / 0.25)

pH = 4.94

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