Ka for the weak acid Hno2 is 4.5x10 ^-4 A) how many grams of solid NaNO2 must be
ID: 1059213 • Letter: K
Question
Ka for the weak acid Hno2 is 4.5x10 ^-4A) how many grams of solid NaNO2 must be added to 1.0 L of 0.15 M HNO2 solution in order to produce a buffer solution with a pH of 4.0? (Assume the added solid doesn't change volume) B) To produce a buffer using NaNO2 and HNO2 that has a better centered "range", what is a more reasonable pH to aim for? Ka for the weak acid Hno2 is 4.5x10 ^-4
A) how many grams of solid NaNO2 must be added to 1.0 L of 0.15 M HNO2 solution in order to produce a buffer solution with a pH of 4.0? (Assume the added solid doesn't change volume) B) To produce a buffer using NaNO2 and HNO2 that has a better centered "range", what is a more reasonable pH to aim for?
A) how many grams of solid NaNO2 must be added to 1.0 L of 0.15 M HNO2 solution in order to produce a buffer solution with a pH of 4.0? (Assume the added solid doesn't change volume) B) To produce a buffer using NaNO2 and HNO2 that has a better centered "range", what is a more reasonable pH to aim for?
Explanation / Answer
The ph of the buffer is calculate by Hendersen equation as
pH = pKa + log [conjugate base]/[acid]
thus 4.0 = (4-log 4.5) + log x/0.15
Solving for x , x =0.675 M
Thus the mass of Na NO2 that must be added to 1.0L of solution = molarity x molar mass
= 0.675Mx69g/mol
= 46.58 g
Part B
T o produce a buffer with better buffereing action the pH should be pKa +1 to pKa -1., and best at pH = pKa
that is ifor this HNO2/NaNO2 buffer the pH should be 3.35 for best buffering action, and reasonably good bufer between 2.35 and 4.35 .
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