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18.A carbon dioxide sample weighing 44.0 g occupies 35.0 L at 127C and 0.800 atm. What is its volume at STP?a.22.4 Lb.31.1 Lc.35.2 Ld.41.0 LAnswer: (a) Learning Objective: 2.6Science Practice: 2.2, 2.3Essential Knowledge: 2.A.2Difficulty Level: easy19.A gas mixture with a total pressure of 300. torr consists of equal masses of Ne (atomic weight 20.) and Ar (atomic weight 40.). What is the partial pressure of Ar in torr?Learning Objective: 2.4Science Practice: 1.4, 6.4Essential Knowledge: 2.A.2Difficulty Level: easy20.Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)Magnesium metal (0.100 mol) and a volume of aqueous hydrochloric acid that contains 0.500 mol of HCl are combined and react to completion. How many liters of hydrogen gas, measured at STP, are produced? 10
Chapter 5 Test BankChang 12ed.22.4 L of H2Answer: (a)Learning Objective: 3.4Science Practice: 2.2, 5.1, 6.4Essential Knowledge: 3.A.2Difficulty Level: mediumFree Response 1:Calcium carbide reacts with water to form calcium hydroxide and acetylene as shown in the chemical equation below. When the acetylene is collected using water displacement, there is water vapor mixed with the acetylene gas. The partial pressure of the water in the mixture depends on the temperature of the water.CaC2(s) + 2 H2O(l) Ca(OH)2(aq) + C2H2(gCalcium carbide is reacted with water and the acetylene is collected by waterdisplacement in a 5.0 x 102mL Erlenmeyer flask. The pressure on the gas is 752 torr and the water temperature is 22.4oC. When all of the calcium carbide has reacted, the volume of the gas mixture collected is 464 mL. The partial pressure of water at 22.4oC is 20.1 torr.a.What is the pressure of the acetylene collected in the Erlenmeyer flask?b.What is the mass of acetylene produced?c.What is the original mass of calcium carbide that was used in this reaction?d.Acetylene is a linear molecule with the structural formula H-C≡C-H. Do you feel that the actual mass of this gas deviates a great deal from the mass you calculated in step b? Explain why or why not.e.Certain gases such as ammonia do not give accurate volume measurements when they are collected over water. Predict a possible reason why the volume of a gas may be inaccurate when it is collected over water and explain why the measurement may be inaccurate.)Scoring Rubric:11
Chapter 5 Test BankChang 12ea.752 torr – 20.1 torr = 732 torr. The total pressure in the flask is dueto the water vapor and acetylene gas. The partial pressure of the acetylene is the total pressure minus the partial pressure of the water. 1 pointfor the correct mathematical calculation.b.To use the gas constant, R, as 0.0821 mol – K / L –atm, the pressure in torr must be converted to atmospheres. 732 torr / 760 torr = 0.963 atm. The temperature must be in Kelvin (22.4 + 273) = 295 K. Using the ideal gas equation (PV = nRT) you calculate the number of moles of acetylene n= 0.963 atm x 0.464 L / (0.0821 mol-K/L-atm x 295 K). n= 0.447 / 24.2 = 0.0185 mol C2H2. This number of moles is (0.0185 mol x 26 g / mol) = 0.481 g of acetylene. 3 points total. 1 pointfor the correct conversions into