F10Q6W8 - CHEM 0110 QUIZ 6 WEEK 8 MONDAY, 1:00 PM October...

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CHEM 0110 QUIZ 6 WEEK 8 MONDAY, 1:00 PM October 18, 2010 NAME_______________________________________________________________________ pV = nRT; u = 2 1 mass molar RT 3 ;R = 0.0821 L atm/mol K = 8.31 J/mol K 1. Assess each of the following statements as True or False. Give your reasoning. a) Volume is directly proportional to Temperature at constant pressure and # of moles of gas. b) Volume is directly proportional to pressure at constant temperature and # of moles c) A gas behaves more ideally at low temperature than at high temperature. 2. A certain gas, in a closed metal container of volume 4.33L, had a pressure of 0.973atm at a temperature of 48 ° C. The mass of this sample of gas was found to be 6.71g. a) Determine the molar mass in g/mol of the gas. b) If the empirical formula of the gas is CH 2 , deduce the molecular formula. ANSWERS 1. a) True. As pV = nRT, as T increases at constant p, V will also increase. b) False. As pV = nRT, if the right-hand side is constant, an increase in V must be accompanied by a decrease in p, which is an inverse proportionality. c) False. A gas is more ideal at high temperature. At low temperature, the collisions between molecules become inelastic (sticky). OR, at low temperature the gas condenses to a liquid. 2. a) The gas density = 6.71g 4.33L = 1.55g/L d = p (MM) RT ; i.e. (MM) = dRT/p (MM) = 1.55 g / L x 0.0821 L atm / mol K x 321 K 0.973 atm = 42.0 g/mol [Or calculate the number of moles of gas, and then molar mass = mass/# of moles] b) Empirical formula mass of CH 2 = 14.0 g/mol = 42.0 g/mol / 3. Molecular formula = 3 (CH 2 ) = C 3 H 6 For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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CHEM 0110 QUIZ 6 WEEK 8 MONDAY, 6:00 PM October 18, 2010 NAME_______________________________________________________________________ pV = nRT; u = 2 1 mass molar RT 3 R = 0.0821 L atm/mol K = 8.31 J/mol K 1. A bulb of volume 1.20L contains N 2 gas at a pressure of 3.60atm and a temperature of 19 o C. The bulb is connected, via a (closed) valve to another bulb, which has a volume of 4.80L and is initially evacuated (no gas, p = 0) a) Determine the mass of N 2 gas in the 1.20L bulb. b) When the valve is opened, the gas expands to fill both bulbs. What is the final gas pressure, if the temperature does not change? 2. Two balloons, one containing Xe gas and the other Ar gas, have the same volume, pressure and temperature. a) Which sample has the greater mass? b) Which sample has the greater average molecular speed? Give your reasoning. ANSWERS 1. (a) Determine the number of moles of N 2 and then the mass. n = pV 3.60 atm x 1.20L = RT 0.0821 L atm/mol K x 292K = 0.180 mol Mass = 0.180 mol x 28.0 g/mol = 5.05g (b) As n and T are constant, we can use p 1 V 1 = p 2 V 2 , with p 1 = 3.60atm, V 1 = 1.20L and V 2 = 1.20 + 4.80 L = 6.00L. p
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F10Q6W8 - CHEM 0110 QUIZ 6 WEEK 8 MONDAY, 1:00 PM October...

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