Download Chapter 1 Review Questions

Chapter 1 Review Questions
Knowledge
1. a.
b.
Because the atomic number is 4, the atom is beryllium (Be).
atomic number = 4
number of = atomic mass – atomic number
neutrons
atomic mass = 9.01
= 9.01 – 4
= 5.01
number of neutrons = ?
= 5
rounded to the nearest whole
number
The atom has 5
neutrons.
c.
d.
e.
f.
2. a.
b.
Beryllium has two valence electrons (as shown in 1.c. and 1.d.).
Be2+
This ion has a net charge of 2 + because it has two valence electrons. Since metals have
a weaker attraction for electrons, it is much easier to lose two electrons than it is to gain
six; so, beryllium loses two electrons and acquires a charge of 2 +.
Because the atom has an atomic number of 16, the atom must be sulfur (S).
atomic number = 16
atomic mass = 32.06
number of neutrons = ?
number of =
neutrons
=
=
=
atomic mass – atomic number
32.06 – 16
16.06
16
rounded to the nearest whole
number
The atom has 16
neutrons.
c.
d.
e.
f.
3. a.
Sulfur has six valence electrons (as shown in 2.c. and 2.d.)
S2–
This ion has a net charge of 2– because it has six valence electrons. Since non-metals
have a stronger attraction for electrons, it is much easier to gain two electrons than it is
to lose six; so, sulfur gains two electrons and acquires a charge of 2–.
Since ionic compounds contain a metal and a non-metal, potassium iodide, KI(s), and
magnesium oxide, MgO(s), are both examples of ionic compounds. Since molecular
compounds contain two non-metals, carbon tetrachloride, CCl4(l), and hydrogen fluoride,
HF(g), are molecular compounds.
b.
c.
A carbon tetrachloride molecule, CCl4(l),
uses covalent bonds to hold the particles
together.
A hydrogen fluoride molecule, HF(g), uses
covalent bonds to hold the particles
together.
A potassium iodide crystal uses ionic
bonds between potassium ions, K+(aq),
and chloride ions, Cl –(aq).
A magnesium oxide crystal uses ionic bonds
between magnesium ions, Mg2+(aq), and
oxide ions, O2–(aq).
4. The ionic bond in the calcium carbonate is a strong bond that holds the ions firmly in place.
As a result, a great deal of heat can be absorbed before the ions have enough energy to
move. The amount of energy absorbed from the fire protects the contents of the safe from
damage. Metals are good conductors of heat, whereas ionic compounds are poor conductors
of heat and act as better insulators.
5. a.
NaF(s) is an ionic compound. This compound will dissolve in water due to dissociation
and be classified as an electrolyte.
b.
CH4(g) is a molecular compound. This compound will not dissolve in water and be
classified as a non-electrolyte.
c.
Li2O(s) is an ionic compound. This compound will dissolve in water due to dissociation
and be classified as an electrolyte.
d.
AlCl3(s) is an ionic compound. This compound will dissolve in water due to dissociation
and be classified as an electrolyte.
e.
C5H12(l) is a molecular compound. This compound will not dissolve in water and be
classified as a non-electrolyte.
6. Dissociation is the separation of an ionic compound into individual ions in a solution. The
following diagram shows sodium and chloride ions forming associations with charged regions
of water molecules.
7. When an ionic compound dissociates, the solute is separated into its constituent ions. The
atoms that form molecules of a molecular compound do not separate when they dissolve.
The individual molecules remain intact within the solution.
8. A concentrated solution of sulfuric acid contains more particles of solute in a given volume of
solvent. Therefore, a concentrated solution may react quicker and for a longer period of time
until all the solute particles have reacted.
9. Cold water on the skin dilutes the acid by increasing the volume of the solvent. This helps
reduce the corrosive effects of the acid because there are fewer solute particles in a given
volume.
Applying Concepts
10. a.
m = 280 g
M = 12(M of C) + 22(M of H) + 11(M of O)
= 12(12.01 g/mol) + 22(1.01 g/mol) +
11(16.00 g/mol)
= 342.34 g/mol
n=?
The sample contains 0.818 mol of sugar.
b.
n = 0.817 900 333 mol
V = 2.00 L
C=?
The molar concentration of the solution is 0.409 mol/L.
11. a.
m = 16.0 g
M = 2(M of K) + 1(M of S) + 4(M of O)
= 2(39.10 g/mol) + (32.06 g/mol) +
4(16.00 g/mol)
= 174.26 g/mol
n=?
The sample contains 9.18 × 10–2 mol of potassium sulfate.
b.
n = 0.091 816 825 4
C=?
The molar concentration of the solution is 0.184 mol/L.
12. parts per million = 100
ppm
graphic
msolute = ?
The solution contains 5.00 × 10–2 g of lead.
13. a. msolvent = 250 g
msolute = 9.5 × 10-6 g
parts per million = ?
b.
c.
d.
The concentration of arsenic in this water is 0.038 ppm.
The concentration of this water is 0.038 ppm, which is above the maximum level of
0.025 ppm allowed by Health Canada, but far below the lethal dose of 60 ppm for a
typical adult.
The people of Bangladesh have significant problems with arsenic contamination in their
drinking water. Because about 18% of the water wells are contaminated with arsenic, at
least 40 million people are thought to be at risk. For thousands of years, a natural source
of the arsenic contamination came from run-off from the Himalayan mountains, which
picks up the arsenic from rock formations and carries it to the fertile plains where the
people live. A more recent source of contamination has been the use of fertilizers and
modern agricultural techniques. These have dramatically intensified the problems.
Napoleon suspected that he was being poisoned while he was held captive on the island
of St. Helena. A few days before his death, Napoleon requested that his doctors make a
full examination of his body, particularly of his stomach. After his death, the doctors
determined that the cause of death was a perforated stomach ulcer that had turned
cancerous. Although this evidence is consistent with the possible effects of long-term
arsenic poisoning, it is not conclusive. Fortunately, Napoleon’s staff kept locks of his hair,
which were then passed down within these families through generations. Eventually,
modern forensic techniques were applied to the hair samples and traces of arsenic were
found.
It is still unclear whether the source of the arsenic was deliberate poisoning or accidental
exposure. One line of research suggested that the pigment used in the wallpaper in his
room may have had trace amounts of arsenic. The arsenic in these pigments may have
been converted into a toxic vapour that could have entered the air in the damp
environment of St. Helena.
14. a.
C = 0.500 mol/L
n=?
The solution contains 0.125 mol of solute.
b.
V = 5.00 L
C = 0.0250 mol/L
n=?
The solution contains 0.125 mol of solute.
15. a.
First, determine the number of moles of solute.
C = 0.146 mol/L
n=?
The solution contains 0.0365 mol of sugar.
Next, determine the mass of solute.
n = 0.0365 mol
M = 12(M of C) + 22(M of H) + 11(M of O)
= 12(12.01 g/mol) + 22(1.01 g/mol) +
11(16.00 g/mol)
= 342.34 g/mol
m=?
The solution contains 12.5 g of sugar.
b.
First, determine the number of moles of solute.
V = 4.00 L
C = 0.150 mol/L
n=?
The solution contains 0.600 mol of potassium sulfate.
Next, determine the mass of solute.
n = 0.600 mol
M = 2(M of K) + 1(M of S) + 4(M of O)
= 2(39.10 g/mol) + (32.06 g/mol) +
4(16.00 g/mol)
= 174.26 g/mol
m=?
The solution contains 105 g of potassium sulfate.
16. a.
First, determine the number of moles of sugar.
m = 3.89 g
M = 12(M of C) + 22(M of H) + 11(M of O)
= 12(12.01 g/mol) + 22(1.01 g/mol) +
11(16.00 g/mol)
= 342.34 g/mol
n=?
Next, determine the volume of solution.
n = 0.011 362 972 5 mol
C = 0.0675 mol/L
V=?
The volume of solution required is 0.168 L.
b.
First, determine the number of moles of potassium sulfate.
m = 6.26 g
M = 2(M of K) + 1(M of S) + 4(M of O)
= 2(39.10 g/mol) + (32.06 g/mol) + 4(16.00 g/mol)
= 174.26 g/mol
n=?
Next, determine the volume of solution required.
n = 0.035 923 333 mol
C = 0.0250 mol/L
V=?
The volume of solution required is 1.44 L.
17. a.
C = 0.783 mol/L
n=?
The solution will require 0.392 mol of sugar.
b.
n = 0.3915 mol
M = 12(M of C) + 22(M of H) + 11(M of O)
= 12(12.01 g/mol) + 22(1.01 g/mol) +
11(16.00 g/mol)
= 342.34 g/mol
m=?
The solution will require 134 g of sugar.
18. a.
C = 0.750 mol/L
V = 1.25 L
n=?
The solution requires 0.938 mol of sodium chloride.
b.
n = 0.9375 mol
M = (M of Na) + (M of Cl)
= (22.99 g/mol) + (35.45 g/mol)
= 58.44 g/mol
m=?
This solution requires 54.8 g of sodium chloride.
19. Vi = 95.0 mL
Ci = 2.30 mol/L
Vf = 95.0 mL - 15.0 mL
= 80.0 mL
Cf = ?
The concentration increased to 2.73 mol/L.
20. Vi = 150 mL
Ci = 3.40 mol/L
Vf = 150 mL + 750 mL
= 900 mL
Cf = ?
The new concentration of the solution is 0.567 mol/L.
21. Water is the solvent in the shampoo because it acts to dissolve the other ingredients.
22. Any of the ingredients besides water could be classified as a solute.
23. The head of an anionic surfactant molecule carries a negative charge. Although a water
molecule is neutral, the end of the molecule containing the oxygen atom has a partial
negative charge and the end of the molecule containing the two hydrogen atoms has a partial
positive charge. As shown in the diagram, the end of the water molecule with the partial
positive charge would be attracted to the negatively charged head of the anionic surfactant
molecule.
24. a.
Vsolute = 109.0 mL
Vsolution = 350.0 mL
(% V/V) = ?
b.
The percent by volume concentration of the ammonium lauryl sulfate solution is 31.14%.
Vsolute = 106.5 mL
Vsolution = 350.0 mL
(% V/V) = ?
c.
The percent by volume concentration of the ammonium laureth sulfate solution is
30.43%.
Vsolute = 12.0 mL
Vsolution = 350.0 mL
(% V/V) = ?
d.
The percent by volume concentration of the ammonium dodecylbenzene sulfonate
solution is 3.43%.
Vsolute = 2.0 mL
Vsolution = 350.0 mL
(% V/V) = ?
The percent by volume concentration of the dimethicone solution is 0.57%.
25. a. Because like charges repel each other, the slightly negative charge on the surface of the
hair repels the negative charge on the head of the anionic surfactant. Since the oily layer
of sebum and other debris is attached to the long tail of hydrocarbons on the anionic
surfactant, this material is washed away as the shampoo is rinsed from the hair.
b. While combing hair, static charge builds up between the comb and the hair. If the comb
has one charge and each hair has the opposite charge, the hair would be attracted to the
comb. Since they have the same charge, adjacent hairs would repel one another and
would tend to separate. The overall effect of a large number of hairs repelling and
separating would be that the hairs would tend to stand up and “fly away.”
26. Water molecules have a partial negative charge on the end of the molecule occupied by the
oxygen atom and a partial positive charge on the end occupied by the hydrogen atoms. The
result is that water molecules can readily dissolve ionic compounds because the positive and
negative ions can be pulled apart and surrounded by the oppositely charged end of water
molecules.
Oily substances are molecular compounds that consist of molecules that do not have
positively or negatively charged areas. In this case, water molecules are not attracted to
these substances. Instead, water molecules attract each other. Since the oil and the water
remain separated (do not mix), water is, therefore, a poor solvent for oil.
27. Given the large number of manufacturers in the hair-care industry, the answers to questions
27.a. and 27.b. will vary. Sample answers are given.
a. The first three ingredients listed are water, ammonium laureth sulfate, and ammonium
lauryl sulfate.
b. There are 20 ingredients in total listed on the bottle of shampoo.
c. All of the ingredients must be safe to put on hair and skin. So, each ingredient would
have to be tested to ensure that it does not irritate the skin and will not damage hair
growth at the root and just below the skin. Since shampoo can sometimes get in your
eyes, ears, and mouth, it should not be excessively irritating to these areas. Given all the
body parts that could be exposed to shampoo in the shower, the product should also not
promote the growth of bacteria or other harmful microbes.
Once the shampoo is rinsed off and goes down the drain and into the sewer system, it
should be easily treatable so it can be released into the environment. Each ingredient
should be compatible with sewage treatment processes and should not have harmful
effects on the environment.
Science 20 © 2006, Alberta Education