# Which weak acid would be best to use when preparing a buffer solution with a pH of 7.7?

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Which weak acid would be best to use when preparing a buffer solution with a pH of 7.7?

An acid with Ka = 1.0 x 10-11

An acid with Ka = 1.7 x 10 –10

An acid with Ka = 3.2 x 10 –7

An acid with Ka = 2.5 x 10 –8

An acid with Ka = 2.5 x 10 –5

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pH = pKa + log ([base conjugate]/[acid])

7.7 = - log Ka + log (1)

Ka = 2 * 10^-8

choose Ka = 2.5 x 10^–8 for best use...

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I have now not attempted your first question due to the fact that I don't see how this can make an acid buffer. Please investigate that you've got submitted the question effectively. The only acid buffer choice is D 1.23 and this blend cannot supply this kind of pH 2nd question: The pH of a buffer is given through the Henderson - Hasselbalch equation: pKa HCOOH = - log Ka = -log( 1.Seventy seven*10^-4) pKa = 3.75 pH = pKa + log ([salt]/[acid] pH = three.Seventy five + log (zero.89/1.12) pH = 3.Seventy five + log zero.795 pH = three.Seventy five + ( - zero.10) pH = three.Seventy five -0.10 pH = three.65 option B

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You need to convert these Ka values to pKa values

To do this pka= -log(Ka)

The pKa value you find that is closest to the pH= 7.7 is the acid you should use.

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