2. A student pipetted exactly 5.00 mL of vinegar into a 250-mL Erlenmeyer flask
ID: 711626 • Letter: 2
Question
2. A student pipetted exactly 5.00 mL of vinegar into a 250-mL Erlenmeyer flask and added about 45 mL of boiled distilled water and a drop of phenolphthalein indicator. A 50 mL buret was rinsed and filled with a 0.1022 M NaOH solution. The initial volume of the buret was read and recorded as 11.28 mL. The NaOH solution was carefully added to the vinegar untila permanent very slight pink coloration was noticed. The buret was read again and recorded as 45.45 mL. Calculate the acidity of the vinegar as percent (w/v) acetic acid.Explanation / Answer
Answer
4.19%
Explanation
Volume of 0.1022M NaOH solution consumed = 45.45ml - 11.28ml = 34.17ml
No of mole of NaOH consumed =(0.1022mole/1000ml)×34.17ml = 3.49×10-3
the reaction between CH3COOH and NaOH is
NaOH + CH3COOH - - - - - > CH3COONa + H2O
this is 1:1 molar reaction
0.00349moles of NaOH react with 0.00349moles of CH3COOH
mass of CH3COOH = 0.00349mol × 60.05g/mol =0.20957g
Acidity as % Acetic acid =( 0.20957g/5.00ml)×100ml = 4.19%
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