AP Chem Unit 03 Exam Part 2 2010

8/3/2019 AP Chem Unit 03 Exam Part 2 2010

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AP Chem. Unit 03 Exam - States of MatterS,L,G & IMFs

MCHS - Anderson Page 1

Part A

YOU MAY USE YOUR CALCULATOR FOR PART A

CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOURANSWERS. It is to your advantage to do this, since you may obtain partial credit if you do and you will receive li

or no credit if you do not. Attention should be paid to significant figures.

Be sure to write all your answers to the questions on the lined pages that follow each question.

1. Equal masses (0.500 g each) of hydrogen and oxygen are placed in an evacuated 4.00 liter flask at

25.0oC. The mixture is allowed to react to completion and the flask is returned to 25.0

oC and allowed to

come to equilibrium. The equilibrium vapor pressure of water at 25.0oC is 23.76 torr.

a. Write and balance an equation for the reaction.

b. What is the total pressure inside the flask before the reaction begins?

c. What is the mass of water vapor in the flask at equilibrium?

d. How many grams of which reactant gas remains at equilibrium?

e. What is the total pressure inside the flask at equilibrium?

f. After the reaction, is there any liquid water present? If so, how many grams? If not, why not?

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2. Propane, C3H8, is a hydrocarbon that is commonly used as fuel for cooking.

(a) Write a balanced equation for the complete combustion of propane gas, which yields CO2(g) and H2O

(b) Calculate the volume of air at 30C and 1.00 atmosphere that is needed to burn completely 10.0 gram

of propane. Assume that air is 21.0 percent O2 by volume.

(c) Calculate the volume of air at STP necessary to completely burn the 10.0 grams of propane.

(d) Assuming that all of the heat evolved in burning 30.0 grams of propane is transferred to 8.00 kilogramof water (specific heat = 4.18 J/g.K), calculate the increase in temperature of water.

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3. The formula and the molecular weight of an unknown hydrocarbon compound are to be determined by elementa

analysis and the freezing-point depression method.

(a) The hydrocarbon is found to contain 93.46 percent carbon and 6.54 percent hydrogen. Calculate theempirical formula of the unknown hydrocarbon.

(b) A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene (molecular weight 147.0) in

25.86 grams of naphthalene (molecular weight 128.2). Calculate the molality of the p-dichlorobenzensolution.

(c) The freezing point of pure naphthalene is determined to be 80.2C. The solution prepared in (b) is

found to have an initial freezing point of 75.7C. Calculate the molal freezing-point depression const

of naphthalene.

(d) A solution of 2.42 grams of the unknown hydrocarbon dissolved in 26.7 grams of naphthalene is foun

to freeze initially at 76.2C. Calculate the apparent molecular weight of the unknown hydrocarbon onthe basis of the freezing-point depression experiment above.

(e) What is the molecular formula of the unknown hydrocarbon?

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STOP

If youve finished part A, you may continue once you turn off your calculator and put it awayYou may N

use your calculator for any of the following questions.


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Part B: For each of the following three reactions, write a balanced equation for the reaction in part (i) and answer

questions about the reaction in part (ii). In part (i) the coefficients should be in the lowest whole numbers. Assume

that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are

extensively ionized. Omit formulas for and ions or molecules that are unchanged by the reaction. You may use a

sheet of paper for scratch work, but only equations that are written in the answer boxes provided will be scored.

4(a) A pea sized piece of Lithium is added to water.

(i) Balanced equation:

(ii) What would happen to the color of the solution if phenolthalein was added to the solution. Why?

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(b) A 0.1 M solution of of silver nitrate is added to a 0.1 M solution of potassium chromate.


(ii) If 1.0 L volumes of 1.0 Msolutions of silver nitrate and potassium chromate are mixed togeth

how many moles of product(s) will be produced? Assume the reaction goes to completion.

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Example:

A strip of magnesium metal is added to a solution of silver(I) nitrate.

(ii) Which substance is oxidized in the reaction?____________________________________________

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(i) Balanced Equation:




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(c) Excess nitric acid is added to solid calcium carbonate.


(ii) Briefly explain why statues made of marble (calcium carbonate) displayed outdoors in urban arare deteriorating.

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(d) solid sodium sulfide has 12 M HCl added to it


(ii) If the contents of the reaction mixture described above are conducted in a lab what is the evide

that a chemical reaction has occurred?

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5. A 2.00 L flask at 27.0oC contains 3.00 grams of Ar(g), SO2(g) and He(g). Answer the following questions about t

gases and in each case explain your reasoning.

a. Which gas has particles with the highest average kinetic energy?

b. Which gas has particles with the highest average velocity?

c. Which gas has the highest partial pressure?

d. Which gas will deviate the most from ideal behavior.

e. Which substance will have the highest boiling point?

f. What changes in temperature and pressure will increase the deviations of all the

gases from ideal behavior?

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6. Use concepts of chemical bonding and/or intermolecular forces to account for each of the follow

observations.

a. The boiling points of water, ammonia, and methane are 100oC. -33oC and -164oC, respectively.b. At 25.0oC and 1.0 atm, chlorine is a gas, bromine is a liquid and iodine is a solid.c. Calcium oxide (2615oC) melts at a much higher temperature than does potassium chloride.(770oCd. Propane is a gas and ethanol is a liquid, even though they have similar molar masses.

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7. The normal boiling and freezing points of argon are 87.3 K and 84.0 K, respectively. The triple point is at 82.7 K

and 0.68 atmosphere.

(a) Use the data above to draw a phase diagram for argon. Label the axes and label the regions in which solid, liquid and gas phases are stable. On the phase diagram, show the position of the normal boiling

point.

(b) Describe any changes that can be observed in a sample of solid argon when the temperature is increafrom 40 K to 160 K at a constant pressure of 0.50 atmosphere.

(c) Describe any changes that can be observed in a sample of liquid argon when the pressure is reduced

from 10 atmospheres to 1 atmosphere at a constant temperature of 100 K, which is well below the cri

cal temperature.

(d) Does the liquid phase of argon have a density greater than, equal to, or less than the density of the sophase? Explain your answer, using information given in the introduction to this question.

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AP Chem Unit 03 Exam Part 2 2010