Concentration Worksheet W 328 1) 6.80 g of sodium chloride are added to 2750 mL of water. Find the mole fraction of the sodium chloride and of the water in the solution. 2) How many grams of magnesium cyanide are needed to make 275 mL of a 0.075 M solution? 3) How many grams of magnesium cyanide would you need to add to 275 mL of water to make a 0.075 molal solution? 4) Explain how to make one liter of a 1.25 molal sodium hydroxide solution. 5) What is the molarity of a solution made when 52 grams of potassium sulfate are diluted to a volume of 4100 mL? 6) The density of ethylene glycol (antifreeze, HOCH2CH2OH) is 1.09 g/mL. How many grams of ethylene glycol should be mixed with 375 mL of water to make a 7.50% (v/v) mixture? 7) Find the volume of a 0.75 M solution if it contains 39 grams of potassium hydroxide. 8) How many grams of hydrochloric acid are present in 3.0 L of a 0.750 M solution? 9) The concentration of oxygen in water at the bottom of a lake is 0.48 g/L and the pressure is 2.5 atm. If water from the bottom is moved by a current upwards to a depth where the pressure is 1.3 atm, what is the concentration of the oxygen in the water at this depth? 10) What is the molarity of a solution in which 0.850 grams of ammonium nitrate are dissolved in 345 mL of solution? 11) Explain how you would make 675 mL of a 0.400 M barium iodide solution. 1. 6.80 g NaCl x 1 mole NaCl = 0.116 mole NaCl 58.45 g NaCl 2750 mL H2O x 1 g H2O x 1 mole H2O = 152.8 mol H2O 1 mL H2O 18 g H2O mole fraction NaCl = 0.116 mole NaCl = 7.59 x 10-4 152.9 mole soln mole fraction H2O = 152.8 mole H2O = 0.999 152.9 mole soln 2. 275 mL H2O x 1 g H2O = 0.275 L H2O 1000 mL H2O 275 L Mg(CN)2 x 0.075 mole Mg(CN)2 x 76.3 g Mg(CN)2 = 1.6 g Mg(CN)2 1 L Mg(CN)2 1 mole Mg(CN)2 3. 275 mL H2O x 1 g H2O x 1 kg H2O = 0.275 kg H2O 1 mL H2O 1 g H2O 0.275 kg H2O x 0.075 mol Mg(CN)2 x 76.3 g Mg(CN)2 = 1.6 g Mg(CN)2 1 kg H2O 1 mole Mg(CN)2 4. 1.25 molal NaOH = 1.25 mole NaOH 1 kg H2O 1.25 mole NaOH x 40 g NaOH = 50.0 g NaOH 1 mole NaOH Measure 50.0 g NaOH and add water to 1 L volume. 5. 52 g K2SO4 x 1 mole K2SO4 = 0.299 mole K2SO4 174 g K2SO4 0.299 mole K2SO4 = 0.073 M 4.100 L K2SO4 6. 375 mL x 0.0750 = 28.125 mL ethylene glycol 28.125 mL ethylene glycol x 1.09 g ethylene glycol/1ml = 30.7 g ethylene glycol 7. 39 g KOH x 1 mole KOH x 1 L KOH = 0.93 L = 930 mL 56 g KOH 0.75 mol KOH 8. 3.0 L soln x 0.750 moles HCl x 36.45 g HCl = 82 g HCl 1 L soln 1 mole HCl 9. 1.3 atm = C 2.5 atm 0.48 g/L 10. 0.850 g NH4NO3 x 1 mole NH4NO3 = 0.0106 mole NH4NO3 80 g NH4NO3  C = (1.3 atm)(0.48 g/L) = 0.25 g/L (2.5 atm) 0.0106 mole NH4NO3 = 0.0307 M 0.345 L NH4NO3 11. 0.675 L BaI2 x 0.400 moles BaI2 = 0.270 moles BaI2 1 L BaI2 0.270 moles BaI2 x 391.1 g BaI2 = 106 g BaI2 1 mole BaI2 Measure 106 g BaI2 into a beaker and add water to 675 mL volume.