JEE Main Chemistry question
What volume of 1.0 M sodium formate solution should be added to 50 mL of 0.5 M formic acid to produce a buffer solution of pH=4.0 (pKa of formic acid=3.80)?
Answer: (B)
Solution
log([salt]/[acid])=0.2 → ratio=1.585. mmol acid=25; mmol salt needed=1.585×25=39.6 mmol → volume (1.0 M)=39.6 mL.