University of Illinois, Urbana Champaign

• CHEM 102

• 1. How many grams of magnesium sulfate should be added to 425 mL of de-ionized water to make a 0.075 M solution? Number of moles of MgSO4 in 425mL of 0.075M solution = 0.075 mol.L-1 × 0.425 L Molar mass of MgSO4 = [24.305+ 32.066+(15.999×4)}] g.mol-1 = 120.367 g.mol-1 Mass of MgSO4 in 425mL of 0.075M solution = (0.075×0.425)mol × 120.367 g.mol-1 = 3.8 g 2. A solution containing 320.4 g of Mg(NO3)2 per liter has a density of 1.114 g/mL. The molarity of the solution is: Number of moles of Mg(NO3)2 in 1L (Molarity) = 320.4g / 148.3 g.mol-1 = 2.160M 3. The term "proof" is defined as twice the percent by volume of pure ethanol in solution. Thus, a solution that is 95% (by volume) ethanol is 190 proof. What is the molarity of ethanol in a 92 proof ethanol/water solution? density of ethanol = 0.80 g/cm3 density of water = 1.0 g/cm3 mol. wt. of ethanol = 46 g/mol v/v% of 92 proof ethanol = (92/2)% = 46% (v/v) Mass of ethanol in 1L of 92 proof ethanol = 1000mL × (46/100) * (0.8 g.ml-1)