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?

SSCE HSC Chemistry Concentration and Molarity: Citric acid, the predominant aci

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 titration ... 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 moles of NaOH used

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Answer

To calculate the moles of NaOH used in the reaction, use the formula:

$n = C \times V$

where:

$C$ is the concentration of NaOH (0.550 mol L⁻¹)
$V$ is the volume of NaOH used in liters (29.50 mL = 0.02950 L).

Thus, we find:

$n_{NaOH} = 0.550 \times 0.02950 = 0.016225 \text{ moles}$

Step 2

Relate moles of NaOH to moles of citric acid

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Answer

Since citric acid is a triprotic acid, it reacts with NaOH in a 1:3 ratio.

Thus:

$n_{H3C6H5O7} = \frac{n_{NaOH}}{3} = \frac{0.016225}{3} = 0.0054083 \text{ moles}$

Step 3

Calculate concentration of citric acid

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Answer

Now, use the number of moles of citric acid to find its concentration in the original lemon juice sample.

Using the formula:

$C = \frac{n}{V}$

where:

$n = 0.0054083$ moles of citric acid
$V = 0.0250$ L (the volume of lemon juice)

Thus, the concentration is:

$C = \frac{0.0054083}{0.0250} = 0.2163 \text{ mol L}⁻¹$

Finally, convert this concentration to grams per liter using the molar mass of citric acid (192.12 g mol⁻¹):

$C_{grams} = 0.2163 \times 192.12 = 41.6 \text{ g L}⁻¹$

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

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

Calculate moles of NaOH used

Relate moles of NaOH to moles of citric acid

Calculate concentration of citric acid

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