ChemLab113-0042 - The conversion to parts per thousand must...

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Unformatted text preview: The conversion to parts per thousand must be made because it is only in that form that a single acceptability standard can be given that applies to all unknowns. The acceptable range for the conventional average deviation is directly proportional to the mass percent, which varies widely among the different Unknowns used. No such variation exists for the average deviation expressed in parts per thousand, which must be no larger than two parts per thousand to be acceptable. Sample Examination Questions 1. What volume of 0.1095 M HCl solution is required to titrate a 0.5822 g sample of a soda ash unknown in which the mass percent Na2C03 is 38.49%? The molar mass of Na2C03 is 105.98 g/mol. 2. Calcium carbonate reacts with HCl according to the following equation. CaCO; (5) + 2 HCl (aq) —> CaCl; (aq) + H2C03 (aq) A certain solid mixture consists of calcium carbonate and some other substance that is neither an acid nor a base. In analyzing a 0.7341 g sample of the solid mixture 40.20 mL of 0.1025 M HCl solution was used. What is the mass percent calcium carbonate in the mixture? The molar mass of CaCD; is 100.1 g/mol. 3. Why is it necessary to perform a preliminary rough titration of your soda ash unknown? 4. What is the average deviation in parts per thousands for the following set of numbers? 37.93, 38.12, 38.09. 58 ...
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