Concentration Review Worksheet
1) If I make a solution by adding 83 grams of sodium hydroxide to 750 mL of water…
a) What is the molality of sodium hydroxide in this solution?
b) What is the percent by mass of sodium hydroxide in this solution?
c) What is the mole fraction of sodium hydroxide in this solution?
2) If I make a solution by adding water to 35 mL of methanol (CH3OH) until the final volume of the solution is 275 mL…
a) What is the molarity of methanol in this solution? (The density of
methanol is 0.792 g/mL)
b) What is the percent by volume of methanol in this solution?
Concentration Review Worksheet Answers
1) If I make a solution by adding 83 grams of sodium hydroxide to 750 mL of water…
To solve problem 1, you need to have calculated for various parts that there are 2.08 moles of NaOH (which has a molar mass of 40 g/mol), that there are 750 grams of water (which has a density of 1 g/mL), and that there are 41.67 moles of water (which has a molar mass of 18 g/mol).
a) What is the molality of sodium hydroxide in this solution?
2.77 m (2.08 mol / 0.75 kg water)
b) What is the percent by mass of sodium hydroxide in this solution?
9.96% (found by finding 83 g / 833 g and multiplying by 100%)
c) What is the mole fraction of sodium hydroxide in this solution?
0.0475 (found by finding 2.08 mol / 43.75 mol)
2) If I make a solution by adding water to 35 mL of methanol (CH3OH) until the final volume of the solution is 275 mL…
When solving this problem, you’ll need to calculate that there are 27.72 grams of methanol (from the density), which is equal to 0.866 mol.
a) What is the molarity of methanol in this solution? (The density of
methanol is 0.792 g/mL)
3.15 M (0.866 mol/0.275 L)
b) What is the percent by volume of methanol in this solution?
12.7% ( (35 mL/275 mL) X 100)
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