General Chemistry I Worksheet #3 Writing and balancing reactions, molecular mass, stoichiometry (unit analysis), % composition and limiting reagent

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1 General Chemistry I Worksheet #3 Writing and balancing reactions, molecular mass, stoichiometry (unit analysis), % composition and limiting reagent 1. Balance each of the following reactions: 1 Na3PO4(aq) + 3 AgNO3(aq) -(reaction arrow)- > 3 NaNO3(aq) + 1 Ag3PO4(s) 4 FeO(s) + 1 O2(g) -(reaction arrow)- > 2 Fe2O3(aq) 1 CH3CH2OH(l) + 3 O2(g) -(reaction arrow)- > 2 CO2(g) + 3 H2O(aq) 2 NI3NH3(s) -(reaction arrow)- > 2 N2(g) + 3 I2(g) + 3 H2(g) 1 Cu(s) + 2 HNO3(aq) -(reaction arrow)- > 1 Cu(NO3)2(aq) + 1 H2(g) 2. Write out the balanced chemical equations (including phases) for the following: a. When solid sodium is added to water, it produces sodium hydroxide and diatomic hydrogen gas. 2 Na(s) + 2 H2O(l) -(reaction arrow)- > 2 NaOH(aq) + H2(g) b. The reaction between solid phosphorous (P4) and bromine (a diatomic liquid) forms solid phosphorous tribromide. 1 P4(s) + 6 Br2(l) -(reaction arrow)- > 4 PBr3(s) c. Aqueous solutions of sodium carbonate and silver(i) nitrate react to form a solution of sodium nitrate and solid silver carbonate. Na2CO3(aq) + 2 AgNO3(aq) -(reaction arrow)- > 2 NaNO3(aq) + Ag2CO3(s) d. Burning liquid gasoline (C8H18). 2 C8H18(l) + 25 O2(g) -(reaction arrow)- > 16 CO2(g) + 18 H2O(l)

2 3. A g sample of a compound made from phosphorous and chlorine is decomposed. Analysis of the products showed that g of phosphorous atoms were produced. How much chlorine does the compound contain? g P + Cl g P g Cl 4. When solid sodium is added to water, it produces sodium hydroxide and hydrogen gas. How many moles of hydrogen gas was produced from 0.8 moles of sodium and excess water? 2 Na(s) + 2 H2O(l) -(reaction arrow)- > 2 NaOH(aq) + H2(g) (0.8 moles Na) (1 mole H2) = 0.4 moles H2 ( 2 mole Na) 5. In your own words, define limiting reagent. It limits how much product you can form. You run out of the limiting reagent before you run out of any other reactant. 6. Calculate the mass percent of sulfur and oxygen in sulfur dioxide, SO2. [(1 S)(32.07 g S / 1 mole S)] x 100 = % S [ g / 1 mole SO2 ] [(2 O)(15.99 g O / 1 mole O)] x 100 = % O [ g / 1 mole SO2 ]

3 7. Styrene oxide has a very pleasant odor and is used as a raw material for the production of phenylethyl alcohol used in perfumes. If the percent composition follows, what is the empirical formula of styrene oxide? C = 79.97% H = 6.71% O = 13.32% (79.97 g C)( 1 mole C ) = / ( g C) (6.71 g H)(1 mole H ) = / (1.008 g H) (13.32 g O)( 1 mole O ) = / = 1 ( g O) C8H8O, MM 120 g/mole If, in a separate experiment, the molecular mass of the sample was found to be about 110 g/mole, what is the molecular formula of styrene oxide? C8H8O, MM 120 g/mole divided by 110 g/mole is about one, so it is both the empirical and molecular formula

4 8. Water reacts with calcium carbide to produce Ca(OH)2 and acetylene. The acetylene produced by this reaction was used to light miner helmet lamps: CaC2(s) + 2 H2O(l) -(reaction arrow)- > Ca(OH)2(s) + C2H2(g) a. What is the molar mass (MM) of acetylene (C2H2)? g/mole (from adding two carbons (at g/mole) with two hydrogens (at g/mole). b. If 52.3 g of water reacts with excess calcium carbide, what mass of acetylene is made? (52.3 g H2O)( 1 mole H2O)(1 mole C2H2)(26.02 g C2H2) = 37.8 g C2H2 (18.01 g H2O)(2 mole H2O) (1 mole C2H2) c. What is the molar mass (MM) of calcium carbide (CaC2)? g/mole (from adding one calcium (at g/mole) with two carbons (at g/mole). d. How much acetylene could be formed if 20.1 g of calcium carbide and 12.5 g of water reacted? Is there a limiting reagent? (20.1 g CaC2)( 1 mole CaC2)(1 mole C2H2)(26.02 g C2H2) = 8.17 g C2H2 CaC2 is limiting (64.10 g CaC2)(1 mole CaC2)(1 mole C2H2) (12.5 g H2O)( 1 mole H2O)(1 mole C2H2)(26.02 g C2H2) = 9.03 g C2H2 ( g H2O)(2 mole H2O)(1 mole C2H2)

5 General Chemistry I Name: Worksheet #4 Writing and balancing reactions, molecular mass, stoichiometry (unit analysis), % composition and limiting reagent Dr. Brosius 1. Balance each of the following reactions: 1 Na3PO4(aq) + 3 AgNO3(aq) 3 NaNO3(aq) + 1 Ag3PO4(s) 4 FeO(s) + 1 O2(g) 2 Fe2O3(aq) 1 CH3CH2OH(l) + 3 O2(g) 2 CO2(g) + 3 H2O(aq) 2 NI3NH3(s) 2 N2(g) + 3 I2(g) + 3 H2(g) 1 Cu(s) + 2 HNO3(aq) 1 Cu(NO3)2(aq) + 1 H2(g) 2. Write out the balanced chemical equations (including phases) for the following: a. When solid sodium is added to water, it produces sodium hydroxide and diatomic hydrogen gas. 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) b. The reaction between solid phosphorous (P4) and bromine (a diatomic liquid) forms solid phosphorous tribromide. 1 P4(s) + 6 Br2(l) 4 PBr3(s) c. Aqueous solutions of sodium carbonate and silver(i) nitrate react to form a solution of sodium nitrate and solid silver carbonate. Na2CO3(aq) + 2 AgNO3(aq) 2 NaNO3(aq) + Ag2CO3(s) d. Burning liquid gasoline (C8H18). 2 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(l)

6 3. A g sample of a compound made from phosphorous and chlorine is decomposed. Analysis of the products showed that g of phosphorous atoms were produced. How much chlorine does the compound contain? g P + Cl g P g Cl 4. When solid sodium is added to water, it produces sodium hydroxide and hydrogen gas. How many moles of hydrogen gas was produced from 0.8 moles of sodium and excess water? 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) (0.8 moles Na) (1 mole H2) = 0.4 moles H2 ( 2 mole Na) 5. In your own words, define limiting reagent. It limits how much product you can form. You run out of the limiting reagent before you run out of any other reactant. 6. Calculate the mass percent of sulfur and oxygen in sulfur dioxide, SO2. [(1 S)(32.07 g S / 1 mole S)] x 100 = % S [ g / 1 mole SO2 ] [(2 O)(15.99 g O / 1 mole O)] x 100 = % O [ g / 1 mole SO2 ]

7 7. Styrene oxide has a very pleasant odor and is used as a raw material for the production of phenylethyl alcohol used in perfumes. If the percent composition follows, what is the empirical formula of styrene oxide? C = 79.97% H = 6.71% O = 13.32% (79.97 g C)( 1 mole C ) = / ( g C) (6.71 g H)(1 mole H ) = / (1.008 g H) (13.32 g O)( 1 mole O ) = / = 1 ( g O) C8H8O, MM 120 g/mole If, in a separate experiment, the molecular mass of the sample was found to be about 110 g/mole, what is the molecular formula of styrene oxide? C8H8O, MM 120 g/mole divided by 110 g/mole is about one, so it is both the empirical and molecular formula

8 8. Water reacts with calcium carbide to produce Ca(OH)2 and acetylene. The acetylene produced by this reaction was used to light miner helmet lamps: CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) a. What is the molar mass (MM) of acetylene (C2H2)? g/mole (from adding two carbons (at g/mole) with two hydrogens (at g/mole). b. If 52.3 g of water reacts with excess calcium carbide, what mass of acetylene is made? (52.3 g H2O)( 1 mole H2O)(1 mole C2H2)(26.02 g C2H2) = 37.8 g C2H2 (18.01 g H2O)(2 mole H2O) (1 mole C2H2) c. What is the molar mass (MM) of calcium carbide (CaC2)? g/mole (from adding one calcium (at g/mole) with two carbons (at g/mole). d. How much acetylene could be formed if 20.1 g of calcium carbide and 12.5 g of water reacted? Is there a limiting reagent? (20.1 g CaC2)( 1 mole CaC2)(1 mole C2H2)(26.02 g C2H2) = 8.17 g C2H2 CaC2 is limiting (64.10 g CaC2)(1 mole CaC2)(1 mole C2H2) (12.5 g H2O)( 1 mole H2O)(1 mole C2H2)(26.02 g C2H2) = 9.03 g C2H2 ( g H2O)(2 mole H2O)(1 mole C2H2)