Question

1.Strontium chloride (SrCl2) is an active ingredient in some toothpastes that reduce the sensitivity of teeth. It readily dissolves in water and has a solubility of 53.8 g/100 mL of water at 20 °C.

a. Using a periodic table, determine the molar mass of SrCl2. Report your answer to two decimal places.

Molecular weight _________________ g/mol

b. A SrCl2 solution was prepared by taking 52.84 g of SrCl2 and dissolving it in enough water to make 2.50 L of solution. Calculate the concentration of this solution. Report your answer to three decimal places.

Concentration _________________ mol/L

2. A solution of potassium iodide (KI) was prepared by dissolving 68.0 g of KI in 525 g of H2O. Calculate the percent by mass of KI in this solution.

Concentration _________________ % mass

Answer 1

a) SrCl2

At. wt of Sr = 87.62 g

At. wt of Cl = 35.5 g

MOl. wt of SrCl2 = 87.62+(2*35.5) = 158.62 g/mol

b) Molarity of SrCl2 solution can be calculated using the formula

M = (Wt./Mol.wt)(1000/V(mL)

Given that, Wt. of SrCl2 = 52.84 g

Mol.wt of SrCl2 = 158.62 g/mol

Volume, V = 2.5 L = 2500 mL

M = (52.84/158.62)(1000/2500) = 0.1332 mol/L

c) percent by mass = (mass of solute/mass of solution)*100

Mass of KI solute = 68.0 g

Mass of solution = Mass of KI + Mass of H2O = 68+525 = 593 g

percent by mass = (68/593)*100 = 11.46% mass