AP CHEMISTRY MIDTERM REVIEW
CHAPTER 4 REVIEW
1. Write the balanced net ionic equation:
H2SO4 + CaCO3 ® CaSO4 + H2O + CO2
2 H+ + CO32- à H2O + CO2
2. Balance the following redox reaction:
MnO2 +4 HBr ® MnBr2 + 2 H2O + Br2
3. Balance the following redox reaction:
8 I- + SO42- + 10 H+ ® 4 I2 + H2S + 4 H2O
4. Balance the following reaction in basic aqueous solution:
5 H2O + 3 SO32- + 2 CrO42- ® 3 SO42- + 2 Cr(OH)3 + 4 OH-
CHAPTER 5 REVIEW
1. Which of the following gases diffuses 4 times faster than C6H8Br3
a. He b. Ar c. Ne (MM of 20) d. O3 e. other
4 = √ ( 320 ) and then x = 20
1 x
2. Calculate the partial pressure of CO in a CO/CO2 mixture if the mole fraction of CO2 is 0.450 and the total pressure is 3.00 atmosphere.
XCO = 1 -0.45 = 0.55 so 0.55 = y so y = 1.65 atm
1 3 atm
3. If 200.0 mL of O2 were collected over H2O at 27°C and 727 torr, calculate the volume of dry O2 at STP. The vapor pressure of H2O at 27°C is 27 torr.
727 – 27 = 700 torr and 700 (200) = 760 (V2) so V2 = 168 mL
300 273
4. Which of the following diffuses at the same rate as CO?
a. CH4 b. C2H4 c. C3H8 d. H2CO e. none
Since CO = 28 g/mol it will be C2H4 because it is also 28 g/mol
5. If 500.0 mL of a gas at 127°C was cooled to -73°C at constant pressure, what would be the final volume of the gas?
500 = V so v = 250 mL
400 200
6. If 2.20 g of CO2 exerts a pressure of 700. torr at 73°C, what pressure would 13.2 g of CO2 exert in the same container at 73°C?
4200 torr
7. If 400.0 mL of H2 at 730. torr was subjected to a pressure of 2.50 atmospheres, what would be the final volume of H2 assuming constant temperature?
154 mL
8. A certain gas occupies a volume of 100 mL at a temperature of 20°C. What will its volume be at 10°C, if the pressure remains constant?
96.6 mL
9. Calculate the pressure required to compress 2 liters of a gas at 700 mm pressure and 20°C into a container of 0.1 liter capacity at a temperature of -150°C?
5877 mm
10. A flask containing H2 at 0°C was sealed off at a pressure of 1 atm and the gas was found to weigh, 4512 g. Calculate the number of moles and the number of molecules of H2 present.
2256 mol and 1.36 x 1027 molecules
11. Using van der waal’s equation, calculate the pressure exerted by 1 mole of carbon dioxide at 0°c in a volume of a) 1.00 liter , and b) 0.05 liter
a = 3.59 L2 atm/mol2 b= 0.0427 L/mol
1.98 atm and 1632 atm
12. Of the following two pairs, which member will more likely deviate from ideal gas behavior? (1) N2 versus CO (2) CH4 versus C2H6
13. What is the partial pressure of each gas in a mixture which contains 40 g He, 56 g N2, and 16 g O2, if the total pressure of the mixture is 5 atmospheres.
4 atm He, 0.8 atm N2 and 0.2 atm O2
14. At standard conditions, 1 liter of oxygen gas weighs almost 1.44 g, whereas 1 liter of hydrogen weighs only 0.09 g. Which gas diffuses faster? Calculate how much faster. H2 4 times faster
15. The root mean square (rms) speed of hydrogen (H2) at a fixed temperature, T, is 1600 m/sec. What is the rms speed of oxygen (O2) at the same temperature?
1600/4 = 400 m/s
Chapters 6 and 16 Review
1. Calculate the quantity of heat required to raise the temperature of 3.78 liters (H2O should have been written in there sorry) from 10°C and 80°C.
q = 4.18 (3780 g) (70) = 1106028 J or 1106 kJ
2. A piece of iron weighing 20.0 g at a temperature of 95.0°C was placed in 100.0 g of water at 25.0°C. Assuming that no heat is lost to the surroundings, what is the resulting temperature of the iron and water? Specific heat: iron = .108 cal/g°C and water = 1.0 cal/g°C
Tf = 26.47 °C
3. Determine DH° for the following reaction of burning ethyl alcohol in oxygen:
C2H5OH (l) + 3 O2 (g) ® 2 CO2 (g) + 3 H2O (l)
DH°f of C2H5OH = - 65.9 kcal/mol
DH°f of CO2 = -94.1 kcal/mol
DH°f of H2O = -68.3 kcal/mol
DH° = -327.2 kcal
4. Given the following reactions:
S (S) + O2 (g) ® SO2 (g) DH = -71.0 kcal
SO2 (g) + ½ O2 (g) ® SO3 (g) DH = -23.5 kcal
Calculate DH for the reaction: S (s) + 3/2 O2 (g) ® SO3 (g)
DH = -94.5 kcal
5. Calculate the standard enthalpy change, DH°, for the combustion of ammonia, NH3 (g), to give nitric oxide, NO (g), and water H2O (l). The enthalpies of formation, DH°f, are –68.32 kcal/mol for water, -11.02 kcal/mol for ammonia, and 21.37 kcal/mol for nitric oxide.
-140.18 kcal/mol
6. Calculate the quantity of heat required to (a) convert a liter of water at 30°C to a liter of water at 60°C, and (b) heat a 1 kg block of aluminum from 30°C to 60°C. Assume the specific heat of water = 1 cal/g°C and aluminum = .215 cal/g°C.
30 kcal for water and 6.45 kcal for Al
7. A chemist expands an ideal gas against a constant external pressure of 700 mm Hg, and finds its volume changes from 50 to 150 liters. He finds that 1.55 kcal of heat have been absorbed in the process. Determine the internal energy change that took place. 24.217 cal = 1 L atm
Remember that E = q + w (w = -pDV) solve for q.
q = +3.78 kcal
8. Exactly one mole of gaseous methane is oxidized at fixed volume and at 25°C according to the reaction CH4 (g) + 2 O2 (g) ® CO2 (g) + 2 H2O (l) If 212 kcal is liberated, what is the change in enthalpy?
DH = -212 kcal/mol (negative because it is liberated or given off)
9. 40 g of ice at 0°C is mixed with 100 g of water at 60°C. What is the final temperature after equilibrium has been established? Heat of fusion of water = 80 cal/g and specific heat = 1 cal/g°C (qmelting ice + qwarming ice water = - qcooling hot water)
Tf = 20 °C
10. Calculate DS for the conversion of one mole of liquid water to vapor at 100°C. Heat of vaporization = 540 cal/g.
18 g/mol (540 cal/g) = 9720 cal/mol
11. A chemist knows that the DH° = 485 kJ for the reaction 2H2 (g) + O2 (g) ®
2 H2O (g) and that DH° = -537 kJ for H2 (g) + F2 (g) ® 2 HF (g). With this
information, he calculated the DH° for 2 H2O (g) + 2 F2 (g) ® 4 HF (g) + O2 (g)
and predicted whether DS° was positive or negative. How?
DH° = -1559 kJ and DS° is positive more moles produced increasing disorder
12. Determine DG° for the reaction
4 NH3 (g) + 5 O2 (g) ® 4 NO (g) + 6 H2O (l)
DG°f of NH3 = -4.0 kcal/mol
DG°f of NO = 20.7 kcal/mol
DG°f of H2O = -56.7 kcal/mol
-241.4 kcal
13. Calculate the equilibrium constant for the following reaction at 25°C
C (graphite) + 2 H2 (g) ® CH4 (g)
DH° for this reaction is –17,889 cal
NOT ENOUGH INFORMATION LOOKED UP VALUES IN TEXT
DH - T DS = DG = - RT ln k
-75 – 298 (0.186) = -130 = -R (298) ln K and k = 1.054
14. If the standard free energy of formation of HI from H2 and I2 at 490°C is –12.1 kJ/mol of HI, what is the equilibrium constant for this reaction?
k = 1.00
CHAPTER 7 REVIEW (no questions provided but you still need to study this material)
CHAPTER 8
1. What is the explanation for the following trends in lattice energies?
NaF = 260 kcal/mol NaCl = 186 kcal/mol
NaCl = 186 kcal/mol KCl = 169 kcal/mol
NaBr = 177 kcal/mol CsCl = 156 kcal/mol
As the size of atoms increase the bond strength between atom decreases.
2. Which molecule of each of the following pairs would exhibit a higher degree of polarity. HCl and HBr, H2O and H2S; BrCl and IF ?
3. Of the following pairs, which member should exhibit the largest dipole moment. Use the electronegativity table. (a) H-O and H-N; (b) H-F and H-Br; (c) C-O and C-S.
4. You are given H, N, O, Ne, Ca, Al, and Zn. Determine which of these atoms (in their ground state) are likely to be paramagnetic. Arrange these elements in the order of increasing paramagnetism.
5. Compare the bond order of He2 and He2+.
6. Which of the following could be the quantum numbers (n,l,ml,ms) for the valence electron in a potassium atom in its ground state?
a. 3,0,0, ½ b. 3,1,1, ½ c. 4,0,0, ½ d. 4,1,1, ½
7. Which of the following elements is diamagnetic?
a. H b. Li c. Be d. B e. C
8. Which of the following could be the quantum numbers (n,l,ml,ms) for the valence electron in a phosphorus atom?
a. 2,0,0, ½ b. 3,4,1, ½ c. 2,1,0, ½ d. 3,1,1, ½
9. Which of the following ions has the smallest ionic radius?
a. O2- b. F- c. Na+ d. Mg2+ e. Al3+
CHAPTER 11 REVIEW
1. Calculate the mole fractions of C2H5OH, and water in a solution made by dissolving 9.2 g of alcohol in 18 g of water.
XH2O = 0.833
2. By how much will 50. grams of water have its freezing point depressed if you add 30. grams of glucose (C6H12O6) to it?
6.21 °C
3. Calculate the molality of an alcohol-water mixture which will not freeze above a temperature of -10°C. (MW of alcohol = 46.0; Kf for water = 1.86°C)
5.37 mol/kg
4. The molal freezing point constant for a certain liquid is 0.500°C. 26.4 g of a solute dissolved in 250 g of this liquid yields a solution which has a freezing point 0.125° below that of the pure liquid. Calculate the molecular weight of this solute.
MW = 422.4 g/mol (which seems really high to meJ)
5. What is the approximate boiling point at standard pressure of a solution prepared by dissolving 234 g of NaCl in 500 g of water?
106.09°C after you add 6.09°C to 100°C.
6. Ethanol boils at 78.5°C. If 10 g of sucrose (C12H2O11) is dissolved in 150 g of ethanol, at what temperature will the solution boil? Assume Kb = 1.20°C/M for the alcohol.
78.7 °C after you add the 0.2°C to 78.5°C
7. The vapor pressures of pure benzene and toluene at 60°C are 385 and 139 Torr, respectively. Calculate (a) the partial pressures of benzene and toluene, (b) the total vapor pressure of the solution, and (c) the mole fraction of toluene in the vapor above a solution with 0.60 mole fraction toluene.
a. 83.4 torr Benzene and 154 torr toluene
b. 237.4 torr
c. XB = 0.351 and XT = 0.649
8. A solution of 20.0 g of a non-volatile solute in 100 g of benzene at 30°C has a vapor pressure 13.4 torr lower than the vapor pressure of pure benzene. What is the mole fraction of solute? Vapor pressure of benzene at 30°C = 121.8 torr.
Xsol = 0.11
9. The vapor pressure of benzene at 75°C is 640 torr. A solution of 3.68 g of a solute in 53.0 g benzene has a vapor pressure of 615 torr. Calculate the molecular weight of the solute. (MW of benzene = 78.0) MW = 136 g
10. A sugar solution was prepared by dissolving 9.0 g of sugar in 500 g of water. At 27°C, the osmotic pressure was measured as 2.46 atm. Determine the molecular weight of the sugar.
Using π = MRT and therefore Molarity = 0.0999 mol/L therefore MW = 180 g
11. Determine the mass of water to which 293 g of NaCl is added to obtain a 0.25 molal solution.
20.05 kg
12. Calculate the normality of a solution containing 2.45 g of sulfuric acid in 2.00 liters of solution.
0.025 mol H+/mol
AP Chemistry
Midterm Review Problems
1. __3___ Fe + __4___ H2O ® _____ Fe3O4 + __4___ H2
a. Balance the equation.
b. Calculate the formula weight for each of the four substances.
55.85, 18.02, 231.55, and 2.02
c. Assume that 100% of 42 available grams of iron react. Calculate the amounts in grams involved for the other three substances. 18.07, 58.04, 2.02
d. Assuming STP, calculate the volume of hydrogen gas produced from the 42 grams of iron. 22.4 L
2. Interpret each of the following four examples using modern bonding
principles.
a. C2H2 and C2H6 both contain two carbon atoms. However, the bond between the two carbons in C2H2 is significantly shorter than that between the two carbons in C2H6.
These carbons are triple bonded which contains one sigma and two pi bonds.
b. The bond angle in the hydronium ion, H3O+, is less than 109.5°, the angle of a tetrahedral.
The lone pair of electrons on the Oxygen is more repulsive than the bonded electron pairs pushing the bonds closer together than the normal tetrahedral.
c. The lengths of the bonds between the carbon and the oxygens in the carbonate ion, CO32-, are all equal and are longer than one might expect to find in the carbon monoxide molecule, CO.
Carbonate has resonance 3 structures that allow the double bonds to move around. One is double bonded while 2 are single bonded, so the average length is between double and single (ex: If a single bond was 0.100 pm and double was .080 pm then 0.1(x2) + 0.08 /3 = 0.093 pm for average length)
d. The CNO- ion is linear.
O – C – N (the C-N bond is a triple bond, the oxygen has the extra electron and there are no lone pairs on the carbon to disrupt the linear shape.)
3. 2 H2 (g) + O2 (g) ® 2 H2O (l)
The reaction above proceeds spontaneously from standard conditions at
298 K.
a. Predict the sign of the entropy change, DS°, for the reaction. Explain.
Negative, less moles and state of matter change is also less entropic
b. How would the value of DS° for the reaction change if the product of the reaction was H2O (g)? still negative but closer to zero
c. What is the sign of DG° at 298 K? Explain.