Question

A sample of limestone was dissolved in acid and the calcium in the limestone determined gravimetrically by precipitating it as calcium oxalate. The precipitate was dried at 100°C for two hours. The process was done in triplicate. The results of the determination were as follows: Mass of sample (a) 0.9342 g (b) 1.2345 g (c) 0.5783 g Mass of dried precipitate (a) 1.0932 g (b) 1.2678 g (c) 0.6893 g (a) Calculate the gravimetric factor for calcium in the precipitate. (b) Calculate the amount of calcium in each of the three precipitates in grams

Answer 1

To find the amount of calcium in the limestone samples, one must calculate the gravimetric factor using the molar masses of calcium and calcium oxalate monohydrate, then multiply the mass of the dried precipitates by this factor.

Step-by-step explanation:

The student is performing a gravimetric analysis to determine the amount of calcium in limestone by precipitating it as calcium oxalate and then drying the precipitate. The gravimetric factor can be calculated using the molar mass of calcium and calcium oxalate.

Gravimetric Factor Calculation

For calcium oxalate monohydrate (CaC2O4•H2O), the molar mass is approximately 146.1 g/mol. Since each mole of calcium oxalate monohydrate contains one mole of calcium, the molar mass of calcium (40.08 g/mol) can be used to calculate the gravimetric factor:

Gravimetric Factor = Molar mass of Ca / Molar mass of CaC2O4•H2O = 40.08 g/mol / 146.1 g/mol

Amount of Calcium in the Precipitates

Using the gravimetric factor, the amount of calcium in each precipitate can be calculated by multiplying the mass of each dried precipitate by the gravimetric factor:

Amount of calcium in sample (a) = Mass of dried precipitate (a) × Gravimetric Factor

Amount of calcium in sample (b) = Mass of dried precipitate (b) × Gravimetric Factor

Amount of calcium in sample (c) = Mass of dried precipitate (c) × Gravimetric Factor

Answer 2

The gravimetric factor is calculated as the ratio of molar mass of calcium to the molar mass of the precipitate, which is 0.2744. To determine the amount of calcium in each sample, this factor is multiplied by the mass of the dried precipitate, yielding 0.2999 g, 0.3480 g, and 0.1891 g of calcium respectively for the given samples.

Step-by-step explanation:

To calculate the gravimetric factor for calcium in the precipitate, which is calcium oxalate monohydrate (CaC2O4·H2O), we first need the molar mass of this compound and the molar mass of calcium.

The molar mass of CaC2O4·H2O is 146.1 g/mol and for calcium (Ca) it is 40.08 g/mol. The gravimetric factor is then calculated as the ratio of the molar mass of calcium to the molar mass of the precipitate:

Gravimetric Factor = (40.08 g/mol) / (146.1 g/mol) = 0.2744

Next, to calculate the amount of calcium in each of the three precipitates in grams, we multiply the mass of the dried precipitate by the gravimetric factor:

• (a) 1.0932 g × 0.2744 = 0.2999 g of Ca
• (b) 1.2678 g × 0.2744 = 0.3480 g of Ca
• (c) 0.6893 g × 0.2744 = 0.1891 g of Ca

The gravimetric analysis provided accurate determination of calcium content in the limestone samples using the precipitation of calcium oxalate and calculating the calcium mass from the gravimetric factor.