Download Chem 305 Unit 2 Exam F16

Unit 2 Exam (Fall2016)
NA = 6.022 x 1023
Name___________________________________
Seat #_______
Lab Section: M
T
W
Th
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. (3.5 pts ea)
1) A chemical bond formed when two atoms share two electrons is a ________ bond; it is best described as
________.
A) double; covalent
B) double; ionic
C) single; covalent
D) single; ionic
E) triple; covalent
2) The number of valence electrons in the acetic acid molecule (CH3 CO2 H) is ________.
A) 0
B) 8
C) 16
D) 24
E) 32
3) The water molecule has a ________ molecular geometry because its central atom has ________ bonds and
________ lone pairs of electrons.
A) bent; two; two
B) linear; two; two
C) pyramidal; three; one
D) tetrahedral; four; zero
E) trigonal; three; one
4) If the elements W, X, Y, and Z have electronegativity values of 1.0, 2.0, 2.5, and 3.5, respectively, which bond is
the least polar?
A) WX
B) WZ
C) XY
D) XZ
E) YZ
5) Consider the molecule SiCl4 . The electronegativity values for Si and Cl are 1.8 and 3.0, respectively. Based on
these values and on consideration of molecular geometry, the Si-Cl bond is ________ and the molecule is
________.
A) polar; polar
B) non-polar; non-polar
C) polar; non-polar
D) non-polar; polar
E) none of the above
6) The covalent bonding model is most useful in describing which of the following compounds?
A) CoCl2
B) MgCl2
C) NiCl2
D) SCl2
E) CaCl2
7) The scientific principle which is the basis for balancing chemical equations is
A) the Law of Conservation of Energy.
B) the Law of Conservation of Mass.
C) the Law of Conservation of Mass and Energy.
D) the Law of Definite Proportions.
E) Avogadro's Law.
8) The smallest possible unit of a covalent compound is a(an)
A) atom.
B) cation.
C) ion
A-1
D) molecule.
E) anion
9) Which is the correct equation for the reaction of magnesium with hydrochloric acid to produce hydrogen and
magnesium chloride?
A) Mg + 2 HCl → H2 + MgCl2
B) Mg + HCl → H + MgCl
C) 2 Mg + 6 HCl → 3 H2 + 2 MgCl2
D) Mg + 2 HCl → 2 H + MgCl2
E) Mg + 3 HCl
→
3 H + MgCl2
10) When the reaction shown is correctly balanced, the coefficients are
C6 H14 (l) + O2 (g)
A) 1, 6, 6, 7
→
CO2 (g) + H2 O (g)
B) 2, 19, 12, 14
C) 1, 3.5, 6, 7
D) 1, 9.5, 6, 7
E) 2, 16.5, 12, 7
11) The balanced equation for the reaction occurring when calcium nitrate solution is mixed with sodium
phosphate solution is
A) 3 Ca(NO3 )2 (aq) + 2 Na 3 PO4 (aq) → Ca3(PO4 )2 (aq) + 6 NaNO3 (aq).
B) 2 Ca(NO3 )2 (aq) + 3 Na 3 PO4 (aq)
→
2 Ca3 (PO4)2 (s) + 6 NaNO3 (aq).
C) 3 CaNO3 (aq) + Na3 PO4 (aq)
Ca3 PO4 (aq) + 3 NaNO3 (s).
D) 3 Ca(NO3 )2 (aq) + 2 Na 3 PO4 (aq) → Ca3(PO4 )2 (s) + 6 NaNO3 (aq).
E) Ca(NO3 )2 (aq) + 2 NaPO4 (aq) → Ca(PO4 )2 (s) + 2 NaNO3 (aq).
→
12) Which statement concerning the mole concept is NOT true?
A) The molar mass of a metal is its atomic weight expressed in grams.
B) The mole concept makes a connection between the mass of a substance and the number of particles or
units of that substance.
C) One mole of any compound contains one mole of atoms.
D) One mole of sodium contains the same number of atoms as one mole of carbon.
E) One mole of water contains the same number of molecules as one mole of ammonia.
13) The oxidation number of phosphorus in the compound PO4 3- is __________.
A) -2
B) -1
C) +8
14) The number of grams in 7.00 moles of N 2 is ________g.
A) 7 × (6.02 × 1023)
B) 14.0
C) 28.0
D) 98.0
E) 196
15) How many molecules are there in 3.00 moles of NH3 ?
A) 4.00
B) 3.00
C) 12.00
D) 1.20 × 1024
E) 1.81 × 1024
.
A-2
D) +2
E) +5
16) In the reaction shown, how many moles of HCl are needed to react with 2.4 moles of Al?
2 Al + 6 HCl
A) 0.8
B) 1.3
C) 4.8
D) 6.4
E) 7.2
→
2 AlCl3 + 3 H2
.
17) In the reaction shown, ________ is the oxidizing agent because it ________.
Ni (s) + CuCl2 (aq)
→
Cu (s) + NiCl2 (aq)
A) Ni; causes reduction
B) Ni; gets reduced
C) Cu2+ ; causes reduction
D) Cu2+ ; gets reduced
E) Ni2+ ; gets reduced
18) How much Ca(NO3 )2 should be weighed out to have 0.650 mol?
A) 66.4 g
B) 97.6 g
C) 107 g
D) 133 g
E) 165 g
.
19) The combination of ions most likely to produce a precipitate is
A) Li+ and PO4 3- .
B) Pb2+ and NO3- .
C) NH4 + and SO4 2- .
D) Cr3+ and OH- .
E) Mg2+ and C2 H3 O2 - .
20) Consider a reaction that has a positive H and a positive S. Which of the following statements is TRUE?
A) This reaction will be nonspontaneous at all temperatures.
B) This reaction will be spontaneous at all temperatures.
C) This reaction will be spontaneous only at high temperatures.
D) This reaction will be nonspontaneous only at high temperatures.
E) It is not possible to determine without more information.
21) Which reaction is an example of both a precipitation and a neutralization?
A) 2 H3 PO4 (aq) + 3 Ca(OH)2 (aq) → Ca3 (PO4)2 (aq) + 6 H2 O (l)
B) FeCl3 (aq) + KOH (aq)
Fe(OH)3 (s) + 3 KCl (aq)
→
NH
)
CO
(s)
2
NH
(g)
+ CO2 (g) + H2 O (l)
C) (
42
3
3
D) H2 SO4 (aq) + Ba(OH)2 (aq) → BaSO4 (s) + 2 H2 O (l)
E) 2 C (s) + O2 (g) → 2 CO (g)
→
A-3
22) 2 AgNO3(aq) + K2 SO4 (aq)
→ 2 KNO3 (aq) + Ag2 SO4 (s)
The net ionic reaction for the balanced equation shown above is
A) Ag+ + N O 3
→
AgNO3 .
2B) 2 K+ + S O 4
→
K2 SO4 .
C) K+ + N O 3
KNO3 .
→
2D) 2 Ag+ + S O 4
→
Ag2 SO4 .
E) No Reaction
23) All of the statements regarding the symbol "ΔH" are correct except
A) It represents the difference between the energy used in breaking bonds and the energy released in
forming bonds in a chemical reaction.
B) It can be called heat of reaction.
C) It can be called enthalpy change.
D) It can be called entropy change.
E) It has a negative value for an exothermic reaction.
24) Which of the following processes have a S > 0?
A) N2 (g) + 3 H2 (g) → 2 NH3 (g)
B) Na 2 CO3 (s) + H2 O(g) + CO2 (g)
→
2 NaHCO3 (s)
C) CH3 OH(l) → CH3 OH(s)
D) CH4 (g) + H2 O (g) → CO(g) + 3 H2 (g)
E) None of the above processes have a S > 0.
25) Consider the reaction shown:
2 CO (g) + O2 (g) → CO2 (g) + 135.2 kcal
This reaction is ________ because the sign of ΔH is ________.
A) endothermic; positive
B) exothermic; positive
C) endothermic; negative
D) exothermic; negative
E) exothermic; neither positive nor negative
26) Consider the reaction shown:
N2 + O2
→
2 NO
ΔH = 43.2 kcal
When 50.0 g of N2 react, ________ kcal will be ________.
A) 43.2; produced
B) 77.1; consumed
C) 77.1; produced
D) 2160; consumed
E) 2160; produced
A-4
27)
2 Al2 O3 (s) → 4 Al (s) + 3 O2 (g)
ΔG = +138 kcal
Consider the contribution of entropy to the spontaneity of this reaction. As written, the reaction is ________,
and the entropy of the system ________.
A) spontaneous; increases
B) spontaneous; decreases
C) non-spontaneous; increases
D) non-spontaneous; decreases
E) non-spontaneous; does not change
28) For a chemical reaction to occur, all of the following must happen except
A) chemical bonds in the reactants must break.
B) reactant particles must collide with enough energy for change to occur.
C) reactant particles must collide with the correct orientation.
D) a large enough number of collisions must occur.
E) chemical bonds in the products must form.
29) Which statement best describes the way a catalyst works?
A) It decreases the value of ΔH.
B) It increases the value of ΔH.
C) It decreases the value of Eact.
D) It increases the value of Eact.
E) It increases the value of ΔG.
30) When a reaction system is at equilibrium
A) there is no more chemistry happening.
B) the amounts of reactants and products are exactly equal.
C) the reaction rate in the forward direction is at a maximum.
D) the reaction rate in the reverse direction is at a minimum.
E) the rates of the forward and reverse directions are exactly equal.
31)
2 SO2 (g) + O2 (g)
2 SO3 (g) + heat
K = 4.8 × 1027
Which statement about this system is not true?
A) At equilibrium SO3 is the predominant substance.
B) Heating the system will cause a decrease in the amount of SO3 .
C) Adding SO2 will cause an increase in the amount of SO3.
D) Removing O2 will cause an increase in the amount of SO3.
E) The large value of K means that the reaction essentially goes to completion.
32) Which change to this reaction system would cause the equilibrium to shift to the right?
N2 (g) + 3 H2 (g)
2 NH3 (g) + heat
A) addition of a catalyst
B) addition of NH3 (g)
C) removal of H2 (g)
D) heating the system
E) lowering the temperature
A-5
33) Consider the following reaction at equilibrium. What effect will increassing the pressure have on the system?
SO2 (g) + NO2 (g)
SO3 (g) + NO(g)
A) The reaction will shift in the direction of reactants.
B) The reaction will shift to decrease the pressure.
C) The equilibrium constant will decrease.
D) The reaction will shift in the direction of products.
E) No change will occur.
34) Carbon disulfide burns in oxygen according to the reaction CS2 + 3 O2 → CO2 + 2 SO2 .
When 30.0 g carbon disulfide was reacted with 35.0g oxygen, what is the limiting reagent?
A) CS2
B) O2
C) CO2
D) SO2
35) When 30.0 g carbon disulfide was reacted with 35.0g oxygen, (same amounts as above), what is the theoretical
yield of SO2?
A) 46.7g
B) 51.1g
C) 62.3g
D) 70.1g
E) 93.3g
.
36) If the percent yield of a reaction is typically 89.3% and the theoretical yield is calculated to be 85.7g, what will
the actual yield be??
A) 47.6g
B) 96.0g
.
C) 62.3g
D) 51.1g
E) 76.5g
A-6
TRUE/FALSE. Answer 'A' on Scantron if the statement is true and 'B' if the statement is false. (3.5 pts ea)
37) _____ Electronegativity decreases as you go down a column of the periodic table.
38) _____ At chemical equilibrium, all chemical reactions stop.
FILL IN THE BLANK. Add the MOST appropriate term to the blank in the sentence. (3pts ea)
39) A reaction that can proceed in either direction is said to be _________________________________.
40) A reaction will stop when we run out of the __________________________ _________________________.
41) In terms of Enthalpy, the condensation of steam to liquid water is favored or
disfavored?____________________.
42) In terms of Entropy, the condensation of steam to liquid water is favored or
disfavored?_____________________.
43) The condensation of steam to liquid water at 75°C is endergonic or exergonic?_________________________.
SHORT ANSWER AND PROBLEM SOLVING.
44) (4 pts) Consider the reaction:
N2(g) + 3 H2(g)
2 NH3(g)
The equilibrium expression for this reaction is: Kc=
45) (6pts) In a double replacement reaction between solutions of calcium sulfate + ammonium phosphate, the two
products formed would be:
__________________________ and _________________________. (Use formulas, not names.)
(Remember to add state symbols.)
46) (4pts) Balance the following chemical reaction;
_____ HCl(g) + _____ MnO2 (s)
→
_____ Cl2 (g) + _____ MnCl2 (aq) + _____ H2 O(l)
47) (4pts) Write the line-bond structure for CH3 CH2 CH=CHCH(CH3)CH 2CH3
48) Determine the molecular formula (3 pts) and number of lone pairs (3pts) of electrons in the following structure.
A-7
49) (4pts) A student mixed the following solutions and made the following associated observations.
Co(s) + Mn(NO3 )2 (aq)
Mn(s) + Sn(NO3 )2 (aq)
Sn(s) + Co(NO3 )2 (aq)
Ca(s) + Mn(NO3 )2 (aq)
→
No Rxn
_____
→
Mn(NO 3)2 (aq) + Sn(s)
_____
→
→
No Rxn
_____
Ca(NO3 )2 (aq) + Mn(s)
_____
Rank the 4 elements at the RIGHT with the most active element at the TOP.
50) (4pts) Consider the reaction:
2 SO2 (g) + O2 (g)
2 SO3 (g)
If the value of the equilibrium constant, Kc, is 283 and the equilibrium concentrations of the reactants are:
[SO2 ]=0.075 M; [O2 ]=0.537 M;
Find the equilibrium concentration of the product, SO3 .
51) In the unbalanced reaction shown, how many grams of oxygen are needed to produce
66 g of carbon monoxide?(6 pts)
C(s) + O2 (g) → CO(g)
52) In 2.5 moles of Li2 CO3 , (4 pts)
a) How many ions are present?
A-8
53) Draw the Lewis Dot Structure for SO2 . Determine its molecular geometry (4pts)
54) Determine G°rxn at 25 °C using the following information.(6 pts)
CaCO3 (s)
→
CaO(s) + CO2(g)
H°= + 179.2 kJ; S°= + 160.2 J/K
The following BONUS QUESTION is worth 8 points.
55) Write the Total, Ionic, and Net Ionic equations for the reactions that happen when solutions of
iron(III) nitrate and sodium hydroxide are mixed. Include all state symbols.
Total:_______________________________________________________________________________________
Ionic:_______________________________________________________________________________________
___________________________________________________________________________________________
Net Ionic:___________________________________________________________________________________
Driving Force:____________
A-9
Solubility Rules for Some Ionic Compounds in Water
Soluble Ionic Compounds
use state symbol (aq)
Except Those Containing:
use state symbol (s)
1. All lithium (Li+), sodium (Na+), potassium
+
(K ), rubidium (Rb+), cesium (Cs+) and
ammonium (NH4+) salts are SOLUBLE.
No common ones
2. All nitrate (NO3-), acetate (C2H3O2-),
chlorate (ClO3- ), and perchlorate (ClO4-) salts
are SOLUBLE
No common ones
3. All chloride (Cl-), bromide (Br-), and iodide
(I-) salts are SOLUBLE.
Pb+2, Ag+, & Hg2+2 are NOT soluble.
Mercury (II) iodide (HgI2) is also NOT soluble.
4. All fluoride (F-) salts are SOLUBLE.
Mg+2, Ca+2, Sr+2, Ba+2, & Pb+2 are NOT soluble.
5. All sulfate (SO4-2) salts are SOLUBLE.
Ca+2, Sr+2, Ba+2, Pb+2, Ag+, Hg2+2, are NOT soluble.
Not Soluble Ionic Compounds
use state symbol(s)
Except Those Containing:
use state symbol (aq)
6. Hydroxide (OH-) and oxide (O-2)
compounds are NOT SOLUBLE
Li+, Na+, K+, Rb+, Cs+, NH4+, & Ba+2, are soluble.
(Ca2+ and Sr2+ are moderately soluble)
7. Sulfide (S-2) salts are NOT SOLUBLE
Li+, Na+, K+, Rb+, Cs+, NH4+, & Ba+2 are soluble.
Li+, Na+, K+, Rb+, Cs+, & NH4+ are soluble.
8. Carbonate (CO3-2), phosphate (PO4-3),
chromate (CrO4-2), oxalate (C2O4-2) & sulfite
(SO32-) salts are NOT SOLUBLE
Soluble compounds are defined as those that dissolve to the extent of 1 g or more per 100 g water.
NOT Soluble compounds are further classified as:
- Slightly soluble, which dissolve to the extent of 0.01 g to 1 g per 100 g water.
- Insoluble, for which less than 0.01 g per 100 g water will dissolve.
SOLUTIONS MADE FROM THE ABOVE SPECIES, WHEN SOLUBLE, ARE FOUND TO EXIST
AS CHARGED PARTICLES AND THUS CONDUCT ELECTRIC CURRENT. THEY ARE
CONSIDERED ELECTROLYTES. WRITE THEM IN IONIZED FORM IN AQUEOUS SOLUTIONS.
SUMMARY OF STRONG AND WEAK ELECTROLYTES
RULE
EXCEPTIONS
1. Most acids are weak electrolytes
Common strong acids (strong electrolytes) are HCl,
HBr, HI, HNO3, H2SO4, HClO3, and HClO4
2. Most bases are weak electrolytes
Strong base hydroxides (strong electrolytes) are those of
Li, Na, K, Rb, Ca, Sr, and Ba.
3. Most soluble salts are strong
electrolytes.
Important weakly ionized salts are HgCl2, Hg(CN)2,
CdCl2, CdBr2, CdI2, and Pb(C2H3O2)2.