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Concentrations of Solutions Practice Problems Vocabulary Use the following terms: Molality, Mole Fraction, Molarity, Percent by Mass, Saturated solution, Unsaturated, Supersaturated solution, Concentration 1. In chemistry, the most commonly used unit of concentration is __________. 2. A(n) ________ contains less than the saturated amount of solute for that solvent and temperature. 3. The amount of solute (in any measurement unit) divided by the amount of solvent or solution (in any measurement unit) is defined by the basic term of ___________. 4. A(n) ________ contains more solute than a saturated solution can usually hold. 5. Dividing the mass of solute by the total mass of solvent and solute will give you the _________. 6. A method of describing concentration which shows the comparison of moles of solute to moles of solution is the ________. 7. _________ is a concentration unit expressed in units of moles of solute per kilogram of solvent. 8. When a solution contains the maximum amount of solute that can be held by that solvent is known as a(n) ______________. Basic Problems – Molarity 9. What is the molarity of the solution formed by mixing .20 moles of sodium hydroxide (NaOH) with enough water to make 150 mL of solution? 10. If .179 moles K2CO3, potassium carbonate, is dissolved in 450 mL of solution, what is the molarity? 11. Calculate the molarity of the solution when 95.5 g of CaCl2, calcium chloride, is dissolved in enough water to make 1.25 L of solution. 12. What is the molarity of a solution consisting of 11.8 g of NaOH dissolved in enough water to make 300 mL of solution? Basic Problems – Molality 13. Calculate the molality of the solution when .0912 mol of silver nitrate is added to .375 kg of water. 14. 630 g of nitric acid, HNO3, are added to 6.5 kg of water. Calculate the molality of this solution. 15. What is the molality of an alloy containing .03 g of silver and 4.75 g of iron? Basic Problems – Mole Fraction 16. What is the mole fraction of methanol (CH3OH) in a solution that contains 1.25 mol of methanol and 2.22 mol of water? 17. A gas mixture contains 26.3 g of nitric oxide (NO) and 36.2 g of oxygen gas (O2). What is the mole fraction of nitric oxide? Basic Problems - % by Mass 18. Calculate the percent by mass of the solute in an aqueous solution of 27.2 g ethanol in 250 g of total solution (after mixing the ethanol and water). 19. Calculate the percent by mass of the solute in an aqueous solution of 6.50 g NaCl in 75.2 g of water 20. Calculate the percent by mass of the solute in an aqueous solution of 2.0 g I2 in 125 g methanol Advanced Problems 21. How much potassium bromide (KBr), in grams, should be added to water to prepare a .50 L of solution with a molarity of .125 M? 22. How many moles of H2SO4 are contained in 225 mL of .750 M H2SO4? 23. How many grams of HCl are contained in 250 mL of .50 M HCl? 24. How many liters of .50 M glucose, C6H12O6, solution will contain exactly 100 g of glucose. 25. The molality of a solution of chlorine and water is .0362 m. This solution contains 3500 g of water. How much chlorine, in grams, was used to prepare this solution? Challenge Problem: The dehydrated form of Epsom salts is magnesium sulfate (MgSO4). a. What is the percent magnesium sulfate by mass in a solution made from 16.0 g MgSO4 and 100 mL of H2O? The density of water is .997 g/mL. b. What is the mole fraction of MgSO4? c. Calculate the molality of the solution. Challenge Problem: Concentrated hydrochloric acid (HCl) is 36.5% HCl by mass. Its density is 1.18 g/mL. a. Calculate the molality of HCl. b. Calculate the molarity of HCl. Challenge Problem: An aqueous solution contains 167 g CuSO4 in 820 mL of solution. The density of the solution is 1.195 g/mL. Calculate the following: a. Molarity b. Percent by mass c. Mole fraction d. Molality of the solution

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