Question

Calcium hypochlorite (Ca(OCl)2, MW = 142.983 g/mol) is often used as the source of the hypochlorite ion (OCl–, MW = 51.452 g/mol) in solutions used for water treatment. A student must prepare 50.0 mL of a 55.0 ppm OCl– solution from solid Ca(OCl)2, which has a purity of 94.0%.

A) Calculate the mass of the impure reagent required to prepare the solution. Assume the density of the solution is 1.00 g/mL.

B) Which of the following methods would work best to accurately prepare 50.0 mL of the 55.0 ppm OCl– solution?

Use an analytical balance to weigh out an amount of reagent larger than what was determined in part A. In a volumetric flask, combine the reagent and water to create a solution with a concentration greater than 55.0 ppm. Use a pipet to transfer a portion of the concentrated solution to a separate 50.0 mL volumetric flask and dilute to the line with water to create a solution with a concentration of 55.0 ppm.

Use an analytical balance to weigh out an amount of reagent larger than what was determined in part A. In a volumetric flask, combine the reagent and water to create a solution with a concentration greater than 55.0 ppm. Use a graduated cylinder to transfer a portion of the more concentrated solution to a 50.0 mL volumetric flask and dilute to the line with water to create a solution with a concentration of 55.0 ppm.

Use an analytical balance to weigh out the amount of reagent determined in part A. Transfer the reagent to a 50.0 mL volumetric flask, add water to the line, and mix thoroughly.

Use an analytical balance to weigh out the amount of reagent determined in part A. Then use a graduated cylinder to measure out 50.0 mL of water. Combine the reagent and water in a 50.0 mL volumetric flask and mix it thoroughly.

Answer 1