Chemistry 1110 R10 Spring 2015 Test 1 Thursday, January 29, 2015 Time: 1 hour 50 minutes Name: Student Number: This test consists of nine pages of questions, a page of useful constants, and a periodic table. Please ensure that you have a complete paper and, if you do not, obtain one from me immediately. There are 41 marks available. Good luck! 1) [5 marks total] Dioxane contains 5.9584 times more carbon by mass than hydrogen, and 3.9684 times more oxygen by mass than hydrogen. Dioxane contains only carbon, hydrogen, and oxygen. a) [3 marks] What is the empirical formula of Dioxane? b) [2 marks] As a gas, Dioxane has a density of 3.7563 g/l at 150 C and 1.5 bar pressure. What is the molecular formula of Dioxane?
2) [5 marks total] Rebaudioside A is a natural sweetener that is extracted from the Stevia leaf. Rebaudioside A contains only carbon, hydrogen, and oxygen. a) [3 marks] A 4835.07-mg sample of Rebaudioside A was burned, and as a result 9682.2 mg of CO2 (44.01 g/mol) and 3153.5 mg of H2O (18.02 g/mol) were collected. What is the empirical formula of Rebaudioside A? b) [2 marks] Chlorine gas (Cl2) effuses 3.693 times faster than Rebaudioside A under the same conditions. What is the molecular formula of Rebaudioside A? 2
3) [2 marks] When 12.0 grams of NaOH (40.0 g/mol) is added to 88.0 grams of water, the resulting solution has a density of 1.1309 g/ml. What is the concentration of the NaOH solution in moles/l? 4) [4 marks] When 10.0 ml of H2SO4 was added to 40.0 ml of NaOH, the concentration of Na2SO4 in the resulting solution was found to be 0.500 M: 2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) In addition, the concentration of the NaOH after reaction (in the resulting solution) was found to be 0.200 M. What were the concentrations of the NaOH and H2SO4 solutions before they were mixed? 3
5) [3 marks] A 277.5-mg sample of 80.0-percent pure CaCl2 (111.0 g/mol) was reacted with excess AgNO3: CaCl2(aq) + 2AgNO3(aq) Ca(NO3)2(aq) + 2AgCl(s) A total of 429.9 mg of AgCl (143.3 g/mol) were collected. What is the percent yield of the reaction? 6) [2 marks] A 25.00-mL aliquot of H2SO4 required 390.0 mg of Al(OH)3 (78.0 g/mol) for complete neutralization: 2Al(OH)3(aq) + 3H2SO4(aq) Al2(SO4)3(aq) + 6H2O(l) What was the molarity of the H2SO4 solution? 4
7) [4 marks] A 1699-mg sample of MCO3 3H2O was dissolved in 20.0 ml of 1.50 M HCl: MCO3 3H2O(s) + 2HCl(aq) MCl2(aq) + CO2(g) + 4H2O(l) Enough water was then added to the mixture to make 250.0 ml of solution. A 25.0-mL aliquot of the solution was then taken and titrated with 12.50 ml of 0.0800 M NaOH: NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) What is the metal, M? 5
8) [4 marks] An 880-mg mixture of NaOH (40 g/mol) and KOH (56 g/mol) was dissolved in water and completely neutralized by 25.0 ml of 0.800 M HCl: NaOH(aq) + HCl(aq) KOH(aq) + HCl(aq) NaCl(aq) + H2O(l) KCl(aq) + H2O(l) What is the mass percent of KOH in the original mixture? 6
9) [4 marks] A 2626-mg sample of a compound of formula M2(NO3)2 was reacted with excess Na2S and 2166.3 mg of M2S collected: M2(NO3)2(aq) + Na2S(aq) M2S(s) + 2NaNO3(aq) What is the metal, M? 7
10) [4 marks] The following apparatus was assembled: NH3 H2S 2 L, 3 bar 3 L, 3 bar 601.36 K 601.36 K When the valve was opened, the following reaction occurred: 2NH3(g) + H2S(g) (NH4)2S(s) Calculate the total pressure inside the system after reaction. 8
11) [4 marks] The molar mass of magnesium lab was carried out exactly as you ll do it in the lab, with the exception that instead of water, a mystery fluid was used. Your job is to use the data given to determine the density of the mystery fluid. You will also need to know that, when the data was analyzed, the molar mass of Mg was determined to be 24.6 g/mol (instead of 24.3 g/mol). The reaction between Mg and HCl is: Mg + 2HCl MgCl2 + H2(g) Give your density in g/ml. Data (units) value Mass Mg (mg) 52.3 Tsol n ( C) 21.4 Patm (torr) 761.2 VPfluid (torr) 20.3 h (mm) 141 Vgas (ml) 53.3 9
Useful Constants R = 0.08205736 L atm mol K 0.083144621 L bar mol K 62.36359 L torr 8.3144621 1 atm = 101325 Pa 760 torr 1 bar = 100,000 Pa mol K J mol K g = 9.80665 m s 2 10