Question

An environmental chemist analyzed the effluent (the released waste material) from an industrial process known to produce the compounds carbon tetrachloride (CC14) and benzoic acid (HC7H5O2), a weak acid that has one acidic hydrogen atom per molecule. A sample of this effluent weighing 0.3518 g was shaken with water, and the resulting aqueous solution required 10.59 mL of 0.1546 M NaOH for neutralization. Calculate the mass percent of HC7H5O2 in the original sample.

Answer 1

The mass percent of benzoic acid in the sample is 55.5%.

The equation of the reaction is; HC7H5O2(aq) + NaOH(aq) ----> NaC7H5O2(aq) + H2O(l)

Number of moles of NaOH reacted = concentration × volume

Number of moles of NaOH reacted = 10.59/1000 L × 0.1546 M

Number of moles of NaOH reacted = 0.0016 moles of NaOH

Since the reaction is 1:1, 0.0016 moles of HC7H5O2 reacted also.

Hence, mass of HC7H5O2 = 0.0016 moles × 122 g/mol = 0.1952 g

Mass percent of HC7H5O2 in the original sample = 0.1952 g/ 0.3518 g × 100 = 55.5%

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