Download EXAM 3 NAME____KEY –Answers highlighted______(1 pt.) Dr

EXAM 3
NAME____KEY –Answers highlighted_______(1 pt.)
CHEM 1211 VSU
100 points total
Multiple Choice, 3 pts. each
Dr. Gosnell
Oct. 28, 2005
1. A precipitate will form when aqueous AgNO3 is added to an aqueous solution of ________.
Look for double displacement reaction products that are insoluble in water on the table.
AgI is insoluble.
a) KNO3
b) Cu(NO3)2
c) KI
d) Ca(ClO4)2
e) NaNO3
2. What is the net ionic equation for the reaction of aqueous lead(II) nitrate with aqueous sodium bromide?
Remember the naming rules and how to write formulas from names.
Pb(NO3)2(aq) + 2 NaBr(aq) → PbBr2(s) + 2 NaNO3(aq) this is the molecular equation
From the solubility table lead bromide is insoluble which is why it has (s) after it. The sodium and nitrate ions
will be spectator ions and cancel.
a) Pb(NO3)2(aq) + 2 NaBr(aq) → PbBr2(aq) + 2 NaNO3(s)
b) Na+(aq) + NO3-(aq) → NaNO3(s)
c) Pb2+(aq) + 2 Br-(aq) → PbBr2(s)
d) Pb2+(aq) + 2 Na+(aq) → PbNa2(s)
e) Pb(NO3)2(aq) + 2 NaBr(aq) → PbBr2(s) + 2 NaNO3(aq)
3. What is the net ionic equation for the reaction of aqueous lithium hydroxide and aqueous nitric acid?
LiOH + HNO3 recall how to write formulas, then do an acid base reaction
a) H+(aq) + LiOH(aq) → H2O(l) + Li+(aq)
c) HNO3(aq) + LiOH(aq) → H2O(l) + LiNO3(aq)
e) LiOH(aq) + H2O(l) → H+(aq) + Li(OH)2(s)
b) H+(aq) + OH-(aq) → H2O(l)
d) Li+(aq) + NO3-(aq) → LiNO3(aq)
4. Write a balanced equation for the reaction of aqueous solutions of baking soda (sodium bicarbonate) and acetic
acid.
a) NaHCO3(aq) + CH3CO2H(aq) → NaCH3CO2(aq) + H2O(l) + CO2(g)
b) 2 NaHCO3(aq) + CH3CO2H(aq) → 2 Na2CO3(aq) + CH4(aq) + 2H2O(l) + CO2(g)
c) NaHCO3(aq) + CH3CO2H(aq) → H2CO3(s) + NaCH3CO2(aq)
d) NaHCO3(aq) + CH3CO2H(aq) → NaOH(aq) + CH3CO2H(aq) + CO2(g)
e) NaHCO3(aq) + CH3CO2H(aq) → CH4(aq) + 2 CO2(g) + O2(g) + NaOH(aq)
5. Which of the following chemical equations is an acid-base reaction?
a) 2 HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq)
b) HCl(aq) + NH3(aq) → NH4Cl(aq)
c) HCl(aq) + AgNO3(aq) → AgCl(s) + HNO3(aq)
d) Ba(OH)2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaOH(aq)
e) 2 NaOH(aq) + CuCl2(aq) → Cu(OH)2(s) + 2 NaCl(aq)
Sn(s) + 2 H+(aq) → Sn2+(aq) + H2(g)
6. Which species in the reaction below undergoes reduction?
Oxidation number goes down (reduction) for hydrogen (+1 to zero).
a) Sn
b) H+
c) Sn2+
d) H2
e) No compound is reduced.
7. Which compound is the oxidizing agent in the reaction shown?
I-(aq) + ClO-(aq) → IO-(aq) + Cl-(aq)
I-(aq) gets oxidized BY ClO-(aq) , so ClO-(aq) is the oxidizing AGENT.
a) I-
c) Cl-
b) H2O
d) IO-
e) ClO-
8. What is the oxidation number of each atom in potassium nitrate, KNO3?
a) K = +1, N = -3, O = -2
d) K = -1, N = +3, O = -2
b) K = +1, N = +5, O = -2
e) K = 0, N = 0, O = 0
c) K = +1, N = -3, O = +2
9. What is the pH of 0.27 M HNO3? pH = -log(.27)=.57
a) 0.57
b) 1.31
c) 1.86
d) 2.70
e) 13.43
10. A 25.00 mL sample of HCl is titrated with 17.13 mL of 0.3150 M NaOH. What is the concentration
of the HCl solution?
Reaction is HClm + NaOH → NaCl(aq) + H2O
molNaOH  MxL  (0.3150M )(0.0173L)  .00545mol
Since reaction is 1:1 ratio, this neutralizes an equal number of moles of HCl.
molHCl 0.00545mol
Molarity 

 0.2158M
L
0.02500 L
a) 0.001360 M
b) 0.1233 M
c) 0.2158 M
d) 0.4597 M
e) 0.7356 M
11. The reaction: AlCl3(aq) + 3 NaOH(aq) → Al(OH)3(s) + 3 NaCl(aq) is an example of a(n) ____ reaction.
a) single displacement
b) double displacement
c) strong acid-strong base
d) gas-forming
12. Which one of the following statements is INCORRECT?
a) Energy is neither created nor destroyed in chemical reactions.
b) Kinetic energy is the energy associated with motion.
c) Exothermic processes transfer heat from the surrounding into the system.
d) Energy is the capacity to do work.
13. How many nutritional calories (on food labels) related to standard units of calories?
a) They are exactly the same units.
c) 1 nutritional calorie = 1000 standard calories
b) 1000 nutritional calories = 1 standard calorie
d) 1 nutritional calorie = 4.184 standard calories
14. Specific heat capacity is
a) the quantity of heat needed to change 1.00 g of a substance by 1.00 K.
b) the mass of a substance that 1.00 J of energy will heat by 1.00 K.
c) the mass of a substance that 1.00 cal of energy will heat by 1.00 K.
d) the temperature change undergone when 1.00 g of a substance absorbs 4.184 J.
e) the quantity of heat required to melt 4.184 g of a substance.
15. Heat capacity is defined as
a) the amount of heat required to raise the temperature of 1 gram of substance by 1 K.
b) the amount of heat required to raise the temperature of a substance by 1 K.
c) the amount of heat required to vaporize a solid or liquid.
d) the amount of heat required to melt a solid.
e) 4.18 cal/g·K.
16. If 136 J is required to change the temperature of 8.75 g of nickel by 35.0 K, what is the
specific heat capacity of nickel?
c
q
136 J

 0.444 J/g·K
mT (8.75 g )(35.0 K )
a) 0.0294 J/g·K
b) 0.311 J/g·K
c) 0.417 J/g·K
d) 0.444 J/g·K
e) 2.25 J/g·K
17. If the same amount of heat is added to 5.00 g samples of each of the metals below, which metal will experience
the smallest temperature change?
Metal
Specific Heat Capicity (J/g·K)
Al
0.897
Au
0.129
Cu
0.385
Fe
0.449
K
0.753
Since change in temp. is in the denominator of the specific heat equation, the one with the smallest change should
have the largest specific heat.
a) Al
b) Au
c) Cu
d) Fe
e) K
18. Which statement is TRUE about a phase change from solid to liquid?
a)
b)
c)
d)
The temperature remains constant even though heat is added, until the phase change is complete.
The temperature rises depending on the heat of fusion.
The specific heat during a phase change continuously changes because of the density change.
All of the above are true.
19. The heat of vaporization of benzene, C6H6, is 30.8 kJ/mol at its boiling point of 80.1 °C. How much heat is
required to vaporize 128 g benzene at its boiling point?


128 g
  50.5kJ
q  H vap xmol  (30.8kJ / mol )
 78.1136 g / mol 
a) 4.04 kJ
b) 18.8 kJ
c) 19.3 kJ
d) 50.5 kJ
e) 4.04 × 103 kJ
20. Which of the following statements is CORRECT?
a) If a reaction occurs at constant pressure, w = ΔE.
b) If a reaction occurs at constant pressure, q = ΔH.
c) If a reaction occurs at constant pressure, q = ΔE.
d) If a reaction occurs at constant volume, ΔE > ΔH.
e) If a reaction occurs at constant volume, w = ΔE.
21. Which of the following thermodynamic quantities are state functions: heat (q), work (w), enthalpy
change (ΔH), and internal energy change (ΔE)?
a) ΔE only
b) q only
c) ΔE and w
d) ΔH and q
e) ΔH and ΔE
22. The equation for the combustion of butane is shown below.
C4H10(g) + 13/2 O2(g) → 4 CO2(g) + 5 H2O()
ΔH° = -2877 kJ
What is the enthalpy change for the following reaction?
16 CO2(g) + 20 H2O() → 4 C4H10(g) + 26 O2(g)
This reaction is the first reaction reverse and multiplied by 4. So ΔH° = -(-2877 kJ) x 4 = +11,51 J
Convert to kJ
a) -5754 kJ
b) -719.2 kJ
c) +719.2 kJ
d) +5754 kJ
e) +1.151 × 104 kJ
23. Determine the heat of vaporization of titanium(IV) chloride given the enthalpies of reaction below.
Ti(s) + 2 Cl2(g) → TiCl4(l)
Ti(s) + 2 Cl2(g) → TiCl4(g)
ΔH = -804.2 kJ
ΔH = -763.2 kJ
Reverse the first reaction, then add the two reactions together to get TiCl4(l) → TiCl4(g)
ΔHvap = -(-804.2 kJ) + (-763.2 kJ)= +41kJ
a) –1567.4 kJ
b) -41.0 kJ
c) +1.054 kJ
d) +41.0 kJ
e) +1567.4 kJ
24. Which of the following chemical equations corresponds to the standard molar enthalpy of formation of N2O?
a) NO(g) + 1/2 N2(g) → N2O(g)
c) 2N(g) + O(g) → N2O(g)
e) 2 N2(g) + O2(g) → 2 N2O(g)
b) N2(g) + 1/2 O2(g) → N2O(g)
d) N2(g) + O(g) → N2O(g)
25. Calculate H rxn for the combustion of gaseous ethanol,
using standard molar enthalpies of formation.
molecule
ΔHfº (kJ/mol)
C2H5OH(g)
-235.3
CO2(g)
-393.5
H2O(g)
-241.8
C2H5OH(g) + 3 O2(g) → 2 CO2(g) + 3 H2O(g)
Recall that ΔHfº for O2 = zero since it’s an element in its standard state.
o
H rxn
  nH 0f ( products)   nH 0f (reac tan ts)  [2 xCO 2  3 H 2 O(g)] - (C 2 H 5 OH)
= -787 – 725.4 –(-235.3) = -1277.1kJ
a) -1747.7 kJ
b) -1277.1 kJ
c) -793.5 kJ
d) -400.0 kJ
e) -83.6 kJ
26. According to the first law of thermodynamics as applied to chemical reactions,
a)
b)
c)
d)
energy is conserved in any reaction.
the enthalpy change in a reaction equals the heat change.
the heat evolved in a chemical reaction is equal and opposite in sign to the work done on the system.
the work done on a system is independent of the pathway.
27. Which one of the following processes is endothermic?
a)
b)
c)
d)
Steam condenses to liquid water.
Propane gas burns in a gas grill.
Water evaporates from your skin after stepping out of the shower.
Water freezes to form ice.
28. Which of the following regions of the electromagnetic spectrum have longer wavelengths than visible light?
1. FM radio waves
2. x-rays
3. microwaves
a) 1 only
b) 2 only
c) 3 only
d) 1 and 2
e) 1 and 3
29. Which of the following regions of the electromagnetic spectrum has the shortest wavelengths?
a) microwave
b) infrared
c) x-ray
d) gamma ray
e) visible
30. A microwave oven emits radiation at a wavelength of 0.500 cm. What is the frequency of this radiation?

c


3x10 8 m / s
 6 x1010 s 1
3
5 x10 m
a) 1.67  10-11 s-1 b) 6.67  10-7 s-1 c) 2.00 s-1
d) 1.50  106 s-1
e) 6.00  1010 s-1
31. The ________ of a photon of light is ________ proportional to its frequency and ________ proportional to its
wavelength.
a) amplitude, directly, inversely
c) energy, directly, inversely
e) velocity, directly, inversely
b) energy, inversely, directly
d) velocity, inversely, directly
32. According to experiments concerned with the photoelectric effect, which of the following will
increase the number of electrons ejected from a metal surface?
1. increasing the wavelength of the light striking the surface
2. increasing the frequency of the light striking the surface
3. increasing the intensity of light striking the surface
a) 1 only
b) 2 only
c) 3 only
d) 1 and 2
e) 2 and 3
33. The Bohr model predicts that the energy of an atom’s electron is ________, meaning that the electron can only
occupy orbitals of specific energies.
a) continuous
b) discontinuous
c) quantized
d) localized
Bonus questions (3 points each)
34. Commercial cold packs consist of solid ammonium nitrate and water. NH4NO3 absorbs 3.30 × 102 J
of heat per gram dissolved in water. In a coffee-cup calorimeter, 4.40 g NH4NO3 is dissolved in
100.0 g of water at 21.0 °C. What is the final temperature of the solution? Assume that the solution
has a specific heat capacity of 4.18 J/g·K.
HeatAbsorbed  (3.30 x10 2 Jx4.40 g )  1452 J
This heat is absorbed from the whole solution (water and ammonium nitrate) and cools it down.
This depends on the specific heat of the solution and the mass of the solution. Find the temperature change.
T 
q
1452 J

 3.3K
cxm (4.18 J / g  K )(104.4 g )
This gives a 3.5°C change, so final temperature = 21.0°C-3.3°C=17.7°C
a) 3.3 °C
b) 17.7 °C
c) 20.2 °C
d) 20.9 °C
e) 24.3 °C
35. For hydrogen, emission energies can by calculated using the Bohr model.
 1
1 
E = -2.18  1018 J/atom  2 - 2 
 nfinal ninitial 
The Lyman series corresponds to transitions from excited electronic states to a final state of n = 1. If the
wavelength of a transition in the Lyman series is 121.5 nm, what is the initial state of the atom?
Find the energy, then put this into the above equation and also put nfinal=1 and solve for ninitial
hc (6.626 x10 34 J  s) x(3x10 8 m / s)
E 

 1.636 x10 18 J
9

121.5 x10 M
a) 2
b) 3
c) 4
d) 5
36. In 3 sentences or less tell what a line spectrum is and how you could see it.
This is energy given off by an element when it is in something like a gas discharge tube. Due to the allowed
electronic transitions, only certain wavelengths (energies) of light will be given off. You can see these
By passing the light through a prism or grating.
Solubility Rules
Soluble compounds
Exceptions
Almost all salts of Na+, K+, NH4+
Salts of nitrate, chlorate, perchlorate and acetate ions
Almost all salts of Cl-, Br-, I-
Halides of Ag+, Hg22+, Pb2+
Compounds containing F-
Fluorides of Mg2+, Ca2+, Sr2+, Ba2+, Pb2+
Salts of sulfate ion
Sufates of Ca2+, Sr2+, Ba2+, Pb2+
Insoluble compounds
Most salts of carbonate, phosphate, oxalate, chromate.
Most metal sulfides.
Most metal hydroxides and oxides.
Exceptions
Salts of NH4+ and alkali metal cations are
soluble.
Ba(OH)2 is soluble.