A buffer solution that has a pH of 4.72 is prepared by mixing of 1M NaOH and 1MHCN. What is the ratio of volumes of the acid to the base? (pKbof CN−=9.28)
A
1 : 1
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B
1 : 2
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C
2 : 1
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D
3 : 1
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Solution
The correct option is C 2 : 1 Let the volume of NaOH be V1 and volume of HCN be V2
M eq of HCN=V2−V1
M eq of NaCN=V1 Now this will form acidic buffer whose pH is given by pH=pKa+log[NaCN][HCN] Now given pKbof CN−=9.28 ∴pKaofHCN=4.72, putting these values in above equation 4.72=4.72+logV1V2−V1
so V1V2−V1=1
Hence V2=2V1