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Form 1 (White)
CHEM 101 Exam 2
Page 1 October 12, 2001 Name_________________________________
Section _______________________________
This exam consists of 7 pages. When the exam begins make sure you have one of each. Print your name at the top of each page now The last page is blank and you may tear if off and use it for scratch paper. Show your work on calculations, this is the only way partial credit can be given. Be sure to include units on calculations, and give answer to the correct number of significant figures. When a blank is not provided make sure you place a box around the correct answer. The exam is 100 points and 50 minutes.
If anything confuses you or is not clear, raise your hand and ask!
Page Points
2 _____ 3 _____ 4 _____ 5 _____ 6 _____ 7 _____
Total _____
USEFUL INFORMATION
Avogadro’s number = 6.022 x 10 23 R = 0.082057 L atm mol-1^ K- R = 8.3145 J mol -1^ K- 1 atm = 760 torr K = oC + 273.
Ideal Gas Law: PV=nRT; P = (d/M)RT Average Kinetic Energy: (KE)avg = (3/2)RT Root-mean-square velocity: urms = [3RT/M] 1/ Effusion rate: r(1)/r(2) = [Mm (2)/M (^) m (1)] 1/
Page 2 Points 8 1) A 3.664 g sample of a monoprotic (one acidic proton) is dissolved in 0.120 L of water. 20.7 mL of a 0.1578 M NaOH solution is required for complete neutralization in a titration. Calculate the concentration (molarity) and molar mass of the acid.
12 2) A test for alcohols (and one you are likely to do in organic chemistry) is the chromic acid test. In this test an alcohol is treated with chromic anhydride ion, HCrO 4 - , which is orange. If the reaction turns an opaque blue-green an alcohol was present. Balance the redox reaction under acidic conditions.
(orange) (opaque blue-green) CH3OH(l) + HCrO 4 - (aq)! CH 2 O(l) + Cr3+(aq)
Identify the oxidizing agent _______________
Identify the reducing agent ________________
Page 4 Points 14 5) Carbon monoxide, CO(g), reacts with molecular oxygen, O2(g), to give carbon dioxide, CO2(g). Initially CO and O 2 are separated as shown below with the conditions as given.
CO O 2
Closed Valve 2.00 L at 0.500 atm
1.00 L at 1.00 atm When the valve is opened, the reaction quickly goes to completion.
a) Write a balanced chemical reaction for this process.
____CO(g) + ____O (^) 2(g)! ____CO2(g) b) Determine what gases remain at the end of the reaction and calculate their partial pressures. The temperature for the reaction is 25 oC.
c) What is the total pressure at the end of the reaction?
d) What is the mole fraction of CO 2 after the reaction is complete?
Page 5 Points 25 6) Nitrogen is the gas used to inflate air bags required in automobiles. Air bags contain sodium azide, NaN3. The azide ion is N 3 -. When a sensor detects a sudden deceleration, it activates an electrical heater which initiates the decomposition of the sodium azide.
a) Balance the air bag reaction (do it by inspection). ____NaN (^) 3(s)! ____Na(s) + ____N 2 (g)
Is this reaction a redox reaction? Circle one. Yes No
a) If the air bag is 13.6 L and bag needs to be inflated to 2.00 atm at 25.0 oC, how many grams of NaN 3 are necessary if you assume the reaction goes to completion? How many grams of Na are produced?
b) If the minimum pressure to which the bag can be inflated to be functional is 1.35 atm, what is the minimum temperature which will allow the airbag to be functional?
