Question

1. How many grams of K2SO4 and how many grams of water are rwquired to make 250.0g of a 0.2000 m solution? (Hint: First find m/m% K2SO4 in a 0.2000 m solution)

2. What is the mole fraction of K2SO4 in an 8.60% (m/v) aqueous solution of K2SO4?

3. If drinking water contains 1 ppm of fluoride, what is the molarity of F- in the water? How many grams of NaF would be required for a day's worth of water for a household? Assume the volume of the solution is 400 gallons (1 gal = 3.785 L)

The local tao p water contains about 100 pm of Ca+2. Convert this to percent Ca+2 (g per 100 g water)

Answer 1

1. 0.2000 m solution means 0.2000 moles of are present in 1000 g of water.

The molar mas of is 174.3 g/mol.

Thus 0.2000 moles of corresponds to of .

Hence, the total mass of solution will be 34.86 + 1000 = 1034.86 g

The mass percent of in the solution is %

The mass of in 250.0 g of 0.2000 m solution is

The mass of water in 250.0 g of 0.2000 m solution is 250-8.42 = 241.6 g

2. The concentration is 8.60 % m/v.

Thus, 100 ml of solution contains 8.60 g of

The density of aqueous solution is not given. let us assume it to be 1 g/ml.

Hence, 100 ml of solution will approximately correspond to 100 g.

The mass of water in solution = 100 - 8.6 = 91.4 g.

The number of moles of water

The number of moles of

The mole fraction of

3.1 ppm fluoride means 1 mg of fluoride ion in 1 L of solution.

The number of moles of fluoride ions in 1 mg are

The molarity of the solution is

400 gallons corresponds to

They contain 100 ppm of Calcium ions.

This corresponds to of calcium ions.

The moalr masses of Ca and NaF are 40 and 42 g/mol.

Hence, 151.4 g of calcium ions will require of NaF