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a 2.00g sample of limestone was dissolved in hydrochloric acid and all the calcium present in the sample was converted to ca2 (aq). excess ammonium oxalate solution, (nh4)2c2o4(aq), was added to the solution to precipitate the calcium ions as calcium oxalate, cac2o4(s). the precipitate was filtered, dried and weighed to a constant mass of 2.43g. determine the percentage by mass of calcium in the limestone sample.



Answer :

A 2.00g sample of limestone was dissolved in hydrochloric acid and all the calcium present in the sample was converted to ca²⁺ (aq). Excess ammonium oxalate solution, (NH₄)₂C₂O₄(aq), was added to the solution to precipitate the calcium ions as calcium oxalate, CaC₂O₄(s). The precipitate was filtered, dried and weighed to a constant mass of 2.43g.The percentage by mass of calcium in the limestone sample is 31.25%

The percentage by mass of calcium in the limestone can be calculate as follows:

Mass of precipitate that is calcium oxalate = 2.43 g

Moles of calcium oxalate = 2.00g /128 g/mol = 0.015625 moles

One mole of calcium atoms make up one mole of calcium oxalate.

so, 0.015625 moles calcium oxalate equal to 0.015625 moles calcium atoms

Mass of  0.015625 moles of calcium :

0.015625 mol × 40 g/mol = 0.625 g

Mass of sample of limestone = 2 g

Percentage of calcium in limestone:

(0.625 g/2 g) x 100 = 31.25%

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