Putting it together, chapter 11
(p.263-264)
19. In group 5A, the element having the smallest atomic radius is (d) N. Check: Atomic radii increase down
the period.
20. In Group IVA, the most metallic element is (d) Sn. C is nonmetal, Si and Ge are metalloids.
21. Which group in the periodic table contains the least reactive elements? (d) noble gases. The electronic
structure dictates reactivity of an element; in order to fill their orbitals, all elements (except noble gases) form
compounds.
22. Which group in the periodic table contains the alkali metals? (a) 1A.
23. An atom of fluorine is smaller than an atom of oxygen. One possible explanation is that, compared to
oxygen, fluorine has (c) a greater nuclear charge. Check: (a) is not a good answer - even though the mass
number of F is larger than that of O, it has little influence on the size of the atom because the electric force is
stronger than gravitational pull; answers (b) and (d) are wrong.
24. If the size of the fluorine atom is compared to the size of the fluoride ion, (c) the ion is larger than the
atom. It has one electron more than protons, and the nuclear attraction on each electron is decreased, so that
the ion expands.
25. Sodium is a very active metal because :(a) it has a low ionization energy. This answer is the best one, even
though all answers are true.
26. Which of the following formulas is not correct? (b) Check: S-. Sulfur needs two electrons to satisfy the
octet rule.
27. The molecule that does not have a polar covalent bond is (d) Cl2. There cannot be polar bonds between
like atoms.
28. Whch of the following molecules is a dipole? (a) HBr. Check: CH4 and CO2 have no dipole moment
because of their symmetry. For H2-see Q.27.
29. Ionic compound is (b) MgF2, all others are covalent (remember that electronegativity of H is 2.1!)
30. Which of the following is a correct Lewis structure? (b) CCl4. Check: There are two double bonds between
C and O in CO2, a single bond in Cl2, and a triple bond in N2.
31. Incorrect Lewis structure is (a) NH2. Nitrogen has 5 valence electrons, another two come from each H, so
that the total number of electrons is 7. Furthermore, in that case, N would be surrounded with 7 electrons,
rather than 8, that is why such a molecule does not exist!
32. The correct Lewis structure for SO2 is: (b) - the double bond resonates between S and two O atoms.
33. CO2 is nonpolar molecule because (c) it has linear structure O=C=O. There cannot be a center for negative
charge because identical atoms are on both sides of C.
34. When a magnesium atom participates in a chemical reaction, it is most likely to (c) lose two electrons.
Check: Mg has the following structure: [Ne] 3s2, and if it loses two electrons it would have [Ne} electronic
structure. Mg has no affinity towards electrons, and losing only one electron would produce even more
unstable electronic configuration.
35. If X represents an element of Group 3A, what is the general formula for its oxide? (d) X2O3. Check: Al is a
representative, see Q.15.
36. Which of the following has the same electron structure as an argon atom? (a) Ca2+. Check: Cl0 and K0 are
elemental atoms, Na+ has [Ne] configuration.
37. As the difference in electronegativity between tow elements decreases, the tendency for the elements to
form a covalent bond (a) increases.
38. Tetrahedral molecule is (c) CH4. NaCl and MgCl2 are ionic compounds, and CO2 is a linear molecule.
39. Which compound has a bent (V-shaped) molecular structure? (d) H2O. Check: NaCl is an ionic compound,
CO2 is a linear molecule, and CH4 is tetrahedral.
40. Which compound has double bonds within its molecular structure? (b) CO2. Check: See Q. 30 and 39.
41. The total number of valence electrons in a nitrate ion (NO3-) is (d) 24. Count -5 electrons come from N, 18
from the three oxygens, and one from the negative charge. The answer in the book (c) 23 is wrong, see p.247.
42. The number of electrons in a triple bond is (c) 6. Each bond contains two electrons.
43. The number of unbonded pairs of electrons in H2O is (c) 2. Water has two unbonded pairs of electrons,
that is why it is V-shaped.
44. Noble gas electron structure is not in (a) Na atom. It would have [Ne] structure if Na atom looses one
electron to become Na+ ion. Sc3+ has [Ar] structure, O2- has [Ne] structure, and Ar is the noble gas.
Putting up Together, chapters 12-13, (p.369-370)
11. Box A contains O2 at pressure of 200 torr. Box B, identical by volume to A, contains twice as many
molecules of CH4 as the molecules of O2 in box A. The pressures are identical. The temperature in box B is:
(c) 400 torr. Reason: P1V1 = n1RT1; P2V2 = n2RT2: n2 = 2 n1. V1=V2. T1=T2. Therefore, P1/n1 = P2/n2.==> P2 =
P1n2/n1 = 2 P1.
12. A 300 mL sample of O2 is collected over H2O at 23oC and 725 torr. If vapor pressure of water at 23oC is
21.0 torr, the volume of dry O2 at STP is: (a) 256 mL. Reason: Ptotal = PH2O + PO2. PO2 = 725 torr – 21.0 = 704
torr of dry O2. P1V1/T1 = P2V2/T2, V2 = (P1V1T2)/(P2T1) = (704 torr x 300 mL x 273 K) / (760 torr x 296 K) =
256 mL.
13. A tank containing n1 = 0.01 mol Ne and n2 = 0.04 mol He shows a pressure of 1 atm. What is the partial
pressure of Ne in the tank? Use the relationship in Q11: P1/n1 = P2/n2.==> P2 = P1n2/n1 = 4 P1. Furthermore, P1
+ P2 = 1 atm. insert P2 into this ==> P1 + 4 P1 = 1 atm,
5 P1 = 1 atm, (c) P1 = 0.2 atm.
14. How many liters of NO2 at STP can be produced from 25.0 g Cu reacting conc. HNO3?
Reaction: Cu(s) + 4 HNO3(aq) ---> Cu(NO3)2(aq) + 2 H2O(l) + 2 NO2(g)
Number of moles of Cu: 25 g / 63.55 g/mol = 0.393 mol and from the eq. 1 mol Cu givens 2 mol of NO2, ==>
number of moles of NO2 is 0.787 mol. (1 mol / 0.787 mol) = (22.4 L / Y), Y = 17.6 L, answer (c).
15. How many liters of butane are required to obtain 2.0 L of CO2?
Reaction 2 C4H10(g) + 13 O2(g) ---> 8 CO2(g) + 10 H2O(g)
There is no math to do. 2 mol butane give 8
mol CO2, therefore 0.5 L butane will give 2.0 L CO2, answer (d).
16. What volume of CO2 at STP can be produced when 15.0 g C2H6 and 50.0 g O2 are reacted?
Reaction: 2 C2H6(g) + 7 O2(g) ---> 4 CO2(g) + 6 H2O(g)
# of moles of C2H6 = 15.0 g/ 30. g/mol = 0.5 mol# of moles of O2 = 50.0 g/ 32.g/mol = 1.56 mol
O2 is the limiting reactant. # of moles of CO2 = 1.56 mol O2 (4 mol CO2 / 7 mol O2) = 0.893 mol.
0.893 mol CO2 x (22.4 L / 1 mol CO2) = 20.0 L, answer (a).
17. The highest density of gases at STP has the one with the highest molecular mass. That is (c) Cl2.
18. What is the density of CO2 at 25oC and 0.954 atm? Strategy: calculate volume from given P,T and then
calculate density at that volume. P1V1/T1 = P2V2/T2, V2 = (P1V1T2)/(P2T1) = (1 atm x 22.4 L x 298 K) / (0.954
atm x 273 K) = 25.6 L. d = 44.01 g/mol / 25.6 L = 1.72 g/mol, answer (a).
19. How many molecules are present in 0.025 mol of H2 gas?
0.025 mol H2 x (6.022 x 1023 molecules / 1 mol H2) = 1.5 x 1022 molecules, two sig. figs., answer (a).
20. 5.60 L of a gas at STP has mass of 13.0 g. Calculate its molar mass. 5.60 L / 22.4 L = 13.0 6 / Y.
Y = 52.0 g, answer (d).
21. Heat of fusion of water is (b) 335 J/g;
22. Heat of vaporization of water is (c) 2.26 kJ/g.
23. Specific heat of water is (a) 4.185 J/g oC
24. Density of water at 4oC is (a) 1.0 g/mL.
25. SO2 can be classified as (d) acid anhydride 26. Water is liquid because of (d) H-bonds.
27. H bonds are important in (a) HF
28. The equation (b) is incorrectly balanced.
29. The equation (c) is not true, it is N2O5 (not NO2), that with water give nitric acid, HNO3.
30. Calculate heat to transfer 85 g water at 25oC to steam at 100oC. Qtot = Qw + Qv.
Qw = 85 g x 4.184 J/g oC x (100oC-25oC) = 26.6 kJ
Qv = 85 g x 2.26 kJ /g = 192.1 kJ
Qtot = 26.6 kJ + 192.1 kJ = 218.8 kJ, answer (a)
o
o
31. 145 g ice at 0.0 C dropped into 75. g of water at 62 C. What exists at thermal equilibrium?
To transfer all ice into water at 0.0oC, one needs Qf = 145 g x 335 J/g = 48.6 kJ
To transfer water from 62oC to 0.0oC, one needs Qw = 75. g x 4/184 J/g oC x (62oC-0oC) = 19.4 kJ
Since Qf > Qw, some ice will melt, and the mixture will be at 0.0oC. The mass of ice that melts is
19400 J / 335 J/g = 57.9 g. Therefore, the mixture consists of (145 g – 58 g) = 87 g ice and (75. g + 58. g) =
133 g water at 0.0oC, answer (a).
32. The formula for iron(II) sulfate heptahydrate is (c), FeSO4 . 7 H2O. The charge of Fe2+, iron(II), balances
the charge of SO42-, and hepta- means 7.
33. The process by which a solid changes directly to a vapor is called sublimation, answer (c).
34. Hydrogen bonding can occur between NH3 and H2O, answer (c). Hydrogen bonding is intermolecular
force occurring when hydrogen is bonded directly to one (or more) of the three most electronegative elements,
N, O, or F. Both water and ammonia satisfy this, so hydrogen bonding between them is possible.
35. A liquid boils when the vapor pressure of the liquid equals the external pressure above the liquid, answer
(a). The liquid can boil below its normal boiling point if the external pressure is lower than 1 atm!
36. Since the boiling point of liquid B is lower than that of liquid A, it will evaporate faster, answer (b).
37. A chunk of 95 g ice at 0.0oC is added to 100. g of water at 60oC. What mass will still be present at
equilibrium? Qw = 100 g x 4.184 J/g oC x (60oC-0oC) = 25.1 kJ. The mass of ice that has melted is 25100 J /
335 J/g = 75.g, hence (b) 20.0 g of ice is still present.
38. Variable composition, answer (b), is not a property of solutions, as a solution is a homogeneous mixture.
39. If NaCl is soluble in water to the extent of 36.0 g NaCl / 100 g H2O at 20 oC, then a solution at 20 oC
containing 45 g NaCl / 150 g H2O would be (d) unsaturated. The saturated solution in 150 g of H2O would
contain 54 g NaCl.
40. Mass percentage of NaCl in solution of 5 g NaCl in 25.g water is 5 g / 30 g x 100% = (a) 16.7%
41. How many grams of 9.0% AgNO3 solution contain 5.3 g AgNO3?
Mass % = mass solute / mass
solution ==> mass solution = mass solute / mass % = 5.3 g / 0.09 g = (c) 59 g.
Putting up Together, chapters 14, (p.370-371)
42. The molarity of a solution containing 2.5 mol of acetic acid in 400. mL of solution is 2.5 mol / 0.4 L = 6.3
M (with two significant figures), answer (d).
43. What volume of 0.300 M KCl will contain 15.3 g KCl? Molar mass of KCl is 74.55
1 mol KCl
1L
15.3 g KCl x  74.55 g KCl  x  0.300 mol KCl  = 0.684 L answer (b).

 

44. What mass of BaCl2 will be required to prepare 200. mL of 0.150 M solution?
1 L   0.150 mol BaCl2   208.2 g BaCl2 
200. mL x 
x
x
=6.25 g, answer (c).
1L
 1000 mL  
  1 mol BaCl2 
Problems 45-47 relate to the reaction CaCO3 + 2 HCl  CaCl2 + H2O + CO2.
45. What volume of 6.0 M HCl will be needed to react with 0.350 mol of CaCO3?
2 mol HCl
1L
1000 mL
0.350 mol CaCO3 x  1 mol CaCO  x  6.0 mol HCl  x  1 L  =117 mL, answer (c).


 

3
46. If 400. mL of 2.0 M HCl react with excess of CaCO3, the volume of CO2 produced, measured at STP, is:
1 L   2 mol HCl   1 mol CO2   22.4 L CO2 
400 mL x 
x
x
x
= 9.0 L CO2, answer (c).
1L
 1000 mL  
  2 mol HCl   1 mol CO2 
47. If 5.3 g CaCl2 are produced in the reaction, what is the molarity of the HCl used if 25 mL of it reacted with
excess of CaCO3?
1 mol CaCl2
2 mol HCl
1000 mL HCl
5.3 g CaCl2 x  110.98 g CaCl  x  1 mol CaCl  x  25 mL HCl  = 3.8 M, answer (a)




2
2
48. If 20.0 g of the nonelectrolyte urea is dissolved in 25.0 g of water the freezing point of the solution will be:
o
1 mol urea 
0.333 mol urea 
C kg H2O 
20.0 g urea x 
= 0.333 mol; tf = 
x 1.86 
= 24.8 oC
 60.06 g urea 
 0.025 kg H2O 
 1 mol urea 
Freezing point of water = 0.0 oC – 24.8 oC = - 24.8 oC, answer (c).
49. When 256 g of nonvolatile, nonelectrolyte unknown were dissolved in 500. g H2O, the freezing point was
found to be -2.79 oC. The molar mass of the unknown solute is:
tf = 2.79 oC = m Kf  molality = 2.79 /Kf = 1.50 m. = 512 g u.n. / 1 kg H2O;
molar mass = 512/1.5 m = 341 g/mol, answer (d).
50. How many milliliters of 6.0 M H2SO4 must you use to prepare 500. mL of 0.20 M H2SO4 solution?
500 mLx 0.20 M 
M1V1 = M2V2, V2 = M1V1/M2 = 
= 17 mL, answer (b).
6.0 M


51. How many milliliters of H2O must be added to 200. mL of 1.40 M HCl to make a solution that is 0.500 M?
V2 = M1V1/M2 = 
200 mLx 1.40 M 
= 560. mL, out of which 200. mL is HCl solution, so 360. mL of
0.500 M


H2O must be added, answer (a).
52. Answer (c), heating of the solution, would most likely increase the solubility of most solids in liquids.
53. If addition of solid into its solution causes the solution to precipitate, the solution is supersaturated, answer
(d).
54. Anion that is soluble with any cation, including Ag+, is NO3-, answer (b).
55. Which of these salts is soluble in water? Look for NH4+, Na+, K+ or NO3-, as their salts are soluble. Answer
(b), NH4Cl is soluble.
56. 40% solution by volume means that 40 mL of solute is dissolved in 100 mL of solution, answer (a).
57. Surface tension is not a colligative property, answer (d).
58. When a solute is dissolved in a solvent, the boiling point of the solution increases, answer (c).
59. The lowest freezing point will be in a solution that has the highest molality. Thus, answer (b).
60. In the process of osmosis, water passes through a semipermeable membrane from the solution that has the
higher concentration of water, (or more dilute solution with respect to solute), answer (b).