CHEMISTRY 11 AP – PERCENTAGE PURITY & PERCENTAGE YIELD WORKSHEET 1) A saturated solution of lithium fluoride, which is sometimes used as a rinse to prevent tooth decay, contains 0.132 g of LiF in 100.0 g of water. Calculate the percentage purity by mass of the LiF. 2) Automotive air bags inflate when solid sodium azide (NaN3) decomposes explosively into its constituent elements. What volume of nitrogen gas is formed if 120 g of 85% pure sodium azide decomposes? Assume STP conditions. 3) What volume of chlorine gas could be produced under STP conditions if 39.8 g of 84.0% pure potassium chloride were reacted with an excess of fluorine gas? 4) The thermite reaction is extremely exothermic, producing temperatures in excess of 2500°C. These high temperatures were used to weld iron tracks together during the early days of the railway. Thermite is a mixture of powdered aluminum and iron (III) oxide (rust) reacting as follows: 2 Al (s) + Fe2O3 (s) → Al2O3 (s) + 2 Fe (s) If 2.44 g of 95% pure aluminum is reacted, how many grams of aluminum oxide can be produced? 5) A 25.0 g sample of calcium oxide is heated with excess hydrochloric acid to produce water and 37.5 g of calcium chloride. What is the percent yield of the reaction? 6) A solution containing 15.2 g of barium bromide is reacted with a solution containing excess sodium phosphate to form 9.5 g of barium phosphate. What is the percentage yield of the reaction? 7) Copper (II) oxide reacts with hydrogen gas to form water and copper metal. From this reaction, 3.6 g of copper metal was obtained with a yield of 32.5%. What mass of copper (II) oxide was reacted with the excess hydrogen gas? 8) A 20.0 g piece of calcium metal reacts with 18.0 mL of water over time. If 10.0 L of hydrogen gas is formed under STP conditions, what is the percentage yield of the reaction? Recall the density of water is 1.00 g/mL. 9) A sample of impure silver with a mass of 0.7294 g was dissolved in excess concentrated nitric acid according to the following unbalanced equation: Ag (s) + HNO3 (aq) → AgNO3 (aq) + NO (g) + H2O (l) Once the nitrogen monoxide gas was vented off in a fume hood, the resulting silver nitrate was reacted with a slight excess of hydrochloric acid to form a precipitate of silver chloride. The dried precipitate was 0.3295 g. What was the percentage purity of the silver sample?
