29, A buffer is diluted to 25% of its initial strength with water, what happens

Question

29, A buffer is diluted to 25% of its initial strength with water, what happens to the buffer capacity? Choices: The buffer capacity decreases to one-quarter. The buffer capacity decreases to one-half The buffer capacity increases by adding one-quarter The buffer capacity increases by adding one-half The buffer capacity remains the same as before. 30. A chemist wants to make a pH 8.00 buffer. Two chemical combinations are available: hypochlororous acid (HC10%,-3.5x10-8) with sodium hypochlorite, or sodium dihydrogen phosphate (NaH,PO, K, 1.3x103) with sodium hydrogen phosphate. Which chemical combination is best for the buffer? What [base]/lacid] ratio should be used? Consider the next four questions together. i0 10 M hnnir arid and 9 1258 M benzoate ion.

Explanation / Answer

29) choice one is correct

30)

sodium dihydrogen phosphate and sodium hydrogen phosphate are best for this buffer . becasue this pair pKa almost nearer to 8.00

pKa = -log (1.3 x 10^-8)

pKa   = 7.89

pH = pKa + log [sodium hydrogen phosphate / sodium dihydrogen phosphate]

8.00 = 7.89 + log [sodium hydrogen phosphate / sodium dihydrogen phosphate]

[sodium hydrogen phosphate / sodium dihydrogen phosphate] = 1.29

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