A sample of sodium carbonate (Na_2CO_3), which is a base (assume the titration e

Question

A sample of sodium carbonate (Na_2CO_3), which is a base (assume the titration endpoint is reached when one proton has been transferred, producing NaHCO_3), with a mass of 0.4820 g is dissolved in water and used to standardize a solution of nitric acid. An endpoint is reached when 43.89 ml of nitric acid has been added. Determine the molarity (in mol/l) of the nitric acid solution. Report your answer to four significant figures. The standardized nitric acid solution Is then used to titrate 22.84 ml of a solution of sodium lactate (NaC_2H_5OCOO). An endpoint is reached when 14.02 ml of nitric acid has been added. Determine the molarity (in mol/L) of the sodium lactate solution. Report your answer to four significant figures.

Explanation / Answer

1. We first determine the # moles in the Na2CO3 sample:

0.4820 g x 1 mol/106 g = 4.55 x 10^-3 moles of Na2CO3

Then we write the reaction, considering the transfer of the proton:

Na2CO3 + HNO3 ----> NaHCO3 + NaNO3

Using stoichiometry:

4.55 x 10^-3 moles of Na2CO3 x (1 mol HNO3/1 mol Na2CO3) = 4.55 x 10^-3 moles of HNO3

4.55 x 10^-3 moles HNO3 / 0.04389 L = 0.1037 M HNO3

2. V1C1 = V2C2 ---> C2 = V1C1/V2 = 0.1037 M HNO3 * 14.02 mL/22.84 mL = 0.06365 M sodium lactate.

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