Citric acid, the predominant acid in lemon juice, is a triprotic acid. A student titrated 25.0 mL samples of lemon juice with 0.550 mol L$^{-1}$ NaOH. The mean titration volume was 29.50 mL. The molar mass of citric acid is 192.12 g mol$^{-1}$. What was the concentration of citric acid in the lemon juice? (A) 1.04 g L$^{-1}$ (B) 41.6 g L$^{-1}$ (C) 125 g L$^{-1}$ (D) 374 g L$^{-1}$

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Citric acid, the predominant acid in lemon juice, is a triprotic acid - HSC - SSCE Chemistry - Question 14 - 2009 - Paper 1

Question 14

Citric acid, the predominant acid in lemon juice, is a triprotic acid. A student titrated 25.0 mL samples of lemon juice with 0.550 mol L$^{-1}$ NaOH. The mean titra... show full transcript

Worked Solution & Example Answer:Citric acid, the predominant acid in lemon juice, is a triprotic acid - HSC - SSCE Chemistry - Question 14 - 2009 - Paper 1

Step 1

Calculate the moles of NaOH used

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Answer

The moles of NaOH can be calculated using the formula:

$ext{Moles NaOH} = ext{Concentration (mol L$^{-1}$)} imes ext{Volume (L)}$

Substituting the given values:

$ext{Moles NaOH} = 0.550 imes 0.0295 = 0.016225 ext{ moles}$

Step 2

Calculate the moles of citric acid

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Answer

Citric acid is a triprotic acid, which means it can react with three moles of NaOH. Therefore, the moles of citric acid can be calculated as:

$ext{Moles Citric Acid} = rac{ ext{Moles NaOH}}{3} = rac{0.016225}{3} = 0.00540833 ext{ moles}$

Step 3

Calculate the concentration of citric acid

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Answer

To find the concentration of citric acid in g L $^{-1}$ , we use:

$ext{Concentration (g L$^{-1}$)} = rac{ ext{Moles Citric Acid} imes ext{Molar Mass}}{ ext{Volume of lemon juice (L)}}$

Substituting the values:

$ext{Concentration} = rac{0.00540833 imes 192.12}{0.025} = 41.6 ext{ g L$^{-1}$}$

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