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# Unit G ReviewThe Mathematics of Chemical Reactions Summary: One of the most useful aspects of chemistry is its ability to make reliable predictions...

Unit G Review—The Mathematics of Chemical Reactions Summary: One of the most useful aspects of chemistry is its ability to make reliable predictions as to the amounts of chemical needed for a proper reaction or the amount of chemical that could be expected to be produced during a chemical change. Using the methods of calculating moles and grams of a substance learned in the last unit, and the mole ratios given in a balanced chemical equation, it is possible to calculate any quantity in an equation given a specific amount of one of the substances in the reaction. Begin with the given amount of the first substance and apply only the ratios necessary to cancel out the original given units and end up with the final required units. Or, use the equation method and set up the problem using the appropriate equations. Be sure to cancel out units as you solve the problem and round off the final answer—but not the intermediate steps—to the correct number of significant digits. Vocabulary: actual yield decanting filtrate mole ratio percent error percent yield stoichiometry theoretical yield Review Questions: Be able to explain the purpose of the following lab procedures: adding an excess of one reactant decanting drying filter paper plus solid folding filter paper heating to constant mass height of solution in funnel placement of funnel tip transferring precipitate washing precipitate Problems: 1. How many grams of bromine are needed to react with 69.4 g of lithium to produce lithium bromide? 2 Li( s ) + Br 2 ( l ) → 2 LiBr( s ) 2. According to the following equation, how many grams of carbon are produced by the complete decomposition of 50.0 g of sucrose? C 12 H 22 O 11 ( s ) → 11 H 2 O( g ) + 12 C( s ) 3. In the equation below, how many grams of nitrogen monoxide are produced from the reaction of 0.25 mol of copper with excess nitric acid? 3 Cu( s ) + 8 HNO 3 ( aq ) → 3 Cu(NO 3 ) 2 ( aq ) + 4 H 2 O( l ) + 2 NO( g ) 4. Potassium chlorate will decompose when heated to form two products, one of which is
oxygen gas. The other is a solid that remains in the test tube. mass of empty test tube 13.85 g mass of test tube and potassium chlorate 38.85 g mass of test tube and final product 29.44 g a. Write the balanced equation for the reaction. b. What mass of potassium chlorate reacted? (Assume all the available potassium chlorate reacted.) c. What is the actual yield of oxygen? d. Determine the theoretical yield of oxygen. e. Calculate the percent error. 5. Copper reacts with aqueous silver nitrate to produce silver metal. The following data were collected: initial mass of copper 1.76 g final mass of copper 1.12 g mass of filter paper 0.91 g mass of filter paper plus silver 3.12 g a. Write the balanced equation for the reaction. b. What mass of copper reacted? c. Calculate the theoretical yield of silver. d. What was the actual mass of silver produced? e. Calculate the percent error for the yield. Unit G Objectives: Recognize that in chemical reactions definite proportions of chemicals react and are produced. Calculate the number of moles of one substance in a chemical reaction when given the number of moles of another substance. Calculate the number of moles of one substance in a chemical reaction when given the mass of another substance. Calculate the mass of one substance in a chemical reaction when given the number of moles of another substance. Calculate the mass of one substance in a chemical reaction when given the mass of another substance. Set up and use a filtration system. Solve gravimetric stoichiometry problems.
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Problems:
1. How many grams of bromine are needed to react with 69.4 g of lithium to produce lithium bromide?
2 Li(s) + Br2(l) → 2 LiBr(s)
Ans) Two moles of lithium reacts with 1 mole of Bromine...

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