CHEM 100 - Answer Key

CHEM 100 D. Miller 1. a) Name Answer Key The unbalanced equation for the reaction of Na2O2 with water is: 2Na2O2(s) + 2H2O(l) ÷ 4NaOH(aq) + O2(g) What mass of oxygen gas will be produced if 3.25 g of sodium peroxide react with a large excess of water? (6) solution map: g Na2O2 ÷ mol Na2O2 ÷ mol O2 ÷ g O2 0.667 g b) What volume (in mL) of 0.120 M HClO4 is required to neutralize 0.256 g Na2CO3? (6) 2HClO4(aq) + Na2CO3(aq) ÷ 2NaClO4(aq) + H2O(l) + CO2(g) solution map: g Na2CO3 ÷ mol Na2CO3 ÷ mol HClO4 ÷ L HClO4 soln ÷ mL HClO4 soln 40.3 mL 2. (3) a) Convert 130 Calories to joules. solution map: Calories ÷ calories ÷ J 5.44 x 105 J b) If 40.0 kJ of energy is absorbed by 500.0 g of water (c = 4.184 J/g AEC) at 10.0 EC, what is the final temperature of the water? (5) solution map: 29.1 EC CHEM 100 D. Miller 3. Name Answer Key Complete and balance each of the following equations. The physical form of the reactants and products does not need to be specified. (4 ea) 2AgNO3 + H2SO4 ÷ Ag2SO4 + 2HNO3 2Al + 6HF ÷ 2AlF3 + 3H2 When each of the following pairs of aqueous solutions is mixed, a precipitate forms. Write the correct chemical formula for the precipitate in each case. (3 ea) iron(III) perchlorate and potassium hydroxide nickel acetate and sodium sulfide Fe(OH)3 NiS Define each of the following. (2 ea) base - A base is a substance that produces OH- when dissolved in water. theoretical yield - This is the maximum amount of product that can form by complete reaction of the limiting reactant. exothermic - A physical or chemical change in which heat is released. Give the name or formula, as appropriate, for each of the following. (1 ea) chlorous acid HClO2 Hg2Cl2 mercury(I) chloride hydrofluoric acid sodium permanganate NaMnO4 HF(aq) magnesium phosphate Mg3(PO4)2 NO2 nitrogen dioxide Write the solution map for the following problem. (3) If the density of a 0.131 M sugar (C12H22O11, M = 342 g/mol) is 1.10 g/mL, what mass of this solution contains 0.15 mol sugar? solution map: mol sugar ÷ L solution ÷ mL solution ÷ g solution CHEM 100 D. Miller 4. Name Answer Key For each of the following multiple-choice questions, circle the letter preceding the correct (best) answer. Only one answer will be accepted for each. (3 ea) When the following equation is completed and balanced, the coefficient for O2 is: H2C2O4 + O2 ÷ A. 1 B. 2 C. 3 D. 4 If a compound dissolves in water to form an aqueous solution that conducts electricity, the compound: A. must be ionic. B. must be molecular. C. may be ionic or molecular. D. contains a metal. The mass percent of nitrogen in ammonium nitrate is 35.0%. The mass of ammonium nitrate that contains 125 g of nitrogen is: A. 35.0 g B. 43.8 g C. 218 g D. 357 g How many nitrogen atoms are contained in 4.92 g Ca(NO3)2? A. 1.2 x 1024 atoms B. 6.0 x 1023 atoms C. 3.6 x 1022 atoms D. 1.8 x 1022 atoms CHEM 100 D. Miller 4. Name Answer Key (continued) Approximately what volume of water must be added to 100. mL of a 0.42 M KCl solution to make a 0.28 M solution of KCl? A. 50 mL B. 100 mL C. 150 mL D. 250 mL Which of the following substances is likely to be insoluble in water? A. magnesium chloride B. lithium sulfate C. iron(II) nitrate D. barium carbonate 5. Chlorine gas can be produced by the following reaction. MnO2 + 4HCl ÷ MnCl2 + 2H2O + Cl2 Assume that 2.69 g of MnO2 (M = 86.94 g/mol) are allowed to react with 4.01 g of HCl (M= 36.46 g/mol). What is the maximum number of moles of Cl2 that could be produced from this reaction? (6) Calculate the yield from each reactant. The one that produces the smaller amount is the limiting reactant and will produce the theoretical yield (maximum amount of product). solution maps: g reactant ÷ mol reactant ÷ mol Cl2 ³ L.R. 0.0275 mol CHEM 100 D. Miller 5. Name Answer Key (continued) How many grams of the reactant in excess remain unreacted? (5) MnO2 is in excess, MnO2 remaining = initial g MnO2 - g MnO2 reacting solution map: g HCl ÷ mol HCl ÷ mol MnO2 reacting 2.69 g MnO2 initially - 2.39 g MnO2 reacting ------------0.30 g MnO2 remaining ÷ g MnO2 reacting 0.30 g