UNIT 3 REVIEW
Part 1
(Pages 265–266) 1. C
2. A 3. 119 4. 162 5. D 6. B 7. 10.7 8. B 9. 6813 10. C 11. A 12. D 13. B 14. D 15. 5142 16. D 17. B Solutions 3.
2
2
2
I
I
I
1 mol
4.52g = 0.0178 mol
253.80 g 0.0178 mol
= 0.119 mol/L = 119 mmol/L 0.150 L
or
4.52 g n
c
c
u
1 mol 253.80 g
u 1
0.119 mol/L = 119 mmol/L 0.150 L
u
4. 405 mg
162 ppm 2.50 L
c
7. pH = –log(2 u 10–11) = 10.7
9. [OH–(aq)] = 10–12.17 mol/L = 6.8 u 10–13 mol/L Part 2
(Pages 266–269)
18. (a) homogenous mixture—a uniform mixture consisting of only one phase
heterogeneous mixture—a nonuniform mixture consisting of more than one phase (b) solute—a substance that is dissolved in a solvent
solvent—a medium in which a solute is dissolved; usually the liquid component of the solution
(c) electrolyte—a solute that forms a solution that conducts electricity nonelectrolyte—a solute that does not conduct electricity in solution
(d) endothermic dissolving—a change in which heat is absorbed by a system from the surroundings, resulting in a decrease in the temperature of the surroundings
exothermic dissolving—a change in which heat is released from a system into the surroundings, resulting in an increase in the temperature of the surroundings
19. (a) acid—a substance that forms a conducting, aqueous solution that turns blue litmus red, neutralizes bases, has a pH less than 7, and reacts with active metals to form hydrogen gas (b) base—a compound that forms a conducting, aqueous solution that turns red litmus blue,
has a pH greater than 7, and neutralizes acids
(c) neutral ionic substance—a crystalline solid compound at SATP that conducts electricity in aqueous molten forms and has a pH of 7
(d) neutral molecular substance—a compound that can be in any state at SATP that does not conduct electricity in any form and has a pH of 7
20. Difference: A hydronium ion is a polyatomic ion formed by the bonding of a hydrogen ion to a lone pair of a water molecule. A hydrogen ion is a simple (monatomic) ion that represents a single proton.
Similarity: Both ions have a 1+ charge. Both were used to explain the acidic properties of solutions.
21. When lead(II) nitrate and potassium iodide are mixed in solid crystal form, there is no reaction. When they are both dissolved in water individually first, then combined, a yellow precipitate of lead(II) iodide forms. This example provides evidence that some substances need to be dissolved in water before they can react.
22. (a) cCa = 150 mg
2.00 L = 75.0 mg/L = 75.0 ppm
The concentration of calcium in the water is 75.0 ppm.
(b) cNaCl = 75.0 mg 1 mol 1 L u 40.08 g
= 1.87 mmol/L
The amount concentration of calcium in the water is 1.87 mmol/L.
23. CH COOH3
100 mL 60 mL
V u
5 mL = 1200 mL = 1.2 L 24. (a) cNaCl = 0.35 mol
= 0.23 mol/L 1.5 L
(b) nMg(NO )3 2 = 25 m L 0.80 mol
u 1 L = 20 mmol (c) VNH3 = 0.246 mol 1 L
2.40 mol
u = 0.103 L
(d) cCuCl2 = 25.00 g 1 mol 134.45 g
u 1
= 0.155 mol/L 1.20 L
u
(e) mNa CO2 3 = 0.0500 L 0.228 mol
u 1 L
105.99 g 1 mol
u = 1.21 g
25. Vici = Vfcf f i i
f
2.70 g/ L c c V
V
25.0 m Lu 4.00 L
16.9 mg/L 26. (a) Vici = Vfcf
i f f i
45 L 3.5 mol/L V V c
c u 11.6 mol/L
The volume of hydrochloric acid required is 14 L. 14 L (b) Procedure
1. Add approximately 22–23 L of water to a large bucket.
3. Measure 14 L of concentrated hydrochloric acid. Pour in a well-ventilated area, wearing eye protection and a lab apron.
4. Slowly transfer the 14 L of concentrated HCl(aq) into the bucket while mixing.
5. Add water to the bucket until the final volume of the diluted solution reaches 45 L.
27. (a) Na2S(s) o 2 Na+(aq) + S2–(aq) [Na+(aq)] = 2.24 mol/L 2
u 1 = 4.48 mol/L [S2–(aq)] = 2.24 mol/L 1
u 1 = 2.24 mol/L (b) Fe(NO3)2(s) o Fe2+(aq) + 2 NO3–(aq)
[Fe2+(aq)] = 0.44 mol/L 1
u 1 = 0.44 mol/L [NO3–(aq)] = 0.44 mol/L 2
u 1 = 0.88 mol/L (c) K3PO4(s) o 3 K+(aq) + PO43–(aq)
[K+(aq)] = 0.175 mol/L 3
u 1 = 0.525 mol/L [PO43–(aq)] = 0.175 mol/L 1
u 1= 0.175 mol/L (d) cCo (SO )2 4 3 8.75 g 1 mol
406.07 g
u 1
= 0.0431 mol/L 0.500 L
u Co2(SO4)3(s) o 2 Co3+(aq) + 3 SO42–(aq) [Co3+(aq)] = 0.0431 mol/L 2
u 1 = 0.0862 mol/L [SO42–(aq)] = 0.0431 mol/L 3
u 1 = 0.129 mol/L 28.
Type Chemistry laboratories Consumer products Environmental studies Method of
expressing concentration
amount concentration percent concentration parts per million
Example 6.0 mol/L NaOH is required for the laboratory synthesis of soap.
The concentration of hydrogen peroxide solutions used for disinfecting cuts is 6%
V/V.
The concentration of carbon dioxide in fresh air ranges from 300 ppm to 600 ppm.
Reason Amount concentrations
specify chemical amounts which is the basis for balancing chemical reaction equations.
Percent concentrations are easier for
consumers to understand.
Parts per million is a convenient way of expressing very small concentrations.
29. The number of digits following the decimal point in a pH value is equal to the number of significant digits in the hydronium ion concentration.
30. (a) pH = –log[H3O+(aq)]
= –log[7.5 u 10–3 mol/L]
= 2.12
(b) pH = –log[HNO3(aq)]
= –log[2.5 u 10–3 mol/L]
= 2.60
31. (a) [H3O+(aq)] = 10–pH
= 10–11.562 mol/L
= 2.74 u 10–12 mol/L (b) [H3O+(aq)] = 10–pH
= 10–3.5 mol/L = 3 u 10–4 mol/L 32.
As the concentration of the hydronium ions decreases, the pH increases exponentially.
33. A theory is tested according to how well it explains current evidence and how well it predicts the results of new experiments. The ability of a theory to predict is the more stringent test.
34. Aquatic environments are themselves chemical solutions. In order to maintain life, the pH value of a body of water must be kept fairly constant. If the pH is altered too far in either direction, the organisms living in the water could die. pH is a useful measurement for environmental scientists because they can easily monitor effects of pollution (e.g., acid deposition) on bodies of water and find solutions to the problem. In manufactured products, the acidity of a solution must be measured accurately to ensure safety and effectiveness of the chemical. The pH scale makes this task easy.
35. (a) [H3O+(aq)] = 10–3 mol/L (fruit juice) [H3O+(aq)] = 10–12mol/L (cleaning solution)
(b) The ratio of the hydronium ion concentration in fruit juice versus cleaning solution is 1 u 10 -3 mol/
12
L 1 u 10 mol/
1 109
= ,
1 L
u or a billion to one.
36. Using a pH meter, determine and record the pH value of each solution. The controlled variables are concentration and temperature.
[Alternatives: measure conductivity, or measure rate of reaction with an active metal]
37. (a) pH = –log [H3O+(aq)]
= –log(5 u 10–7 mol/L) = 6.3
The colour of the flowers would be pink.
(b) pH = –log [H3O+(aq)]
= –log(7.9 u 10–6 mol/L) = 5.10
The colour of the flowers would be blue.
38. When referring to acids, the term “weak” indicates the degree of reaction with water. It has nothing to do with concentration. In scientific contexts in which both strong/weak and concentrated/dilute may be used in the same discussion, it is essential to use the terms as defined in science.
39. nKHC H O4 4 6= 0.150 mol 0.1000 L
u 1 L
= 0.0150 mol
4 4 6
KHC H O
m = 0.0150 mol 188.19 g
1 mol u
= 2.82 g or mKHC
4H4O6= 0.150 mol
0.1000 L u 188.19 g
1 L u 1 mol
= 2.82 g
The mass of potassium hydrogen tartrate required is 2.82 g.
40. Procedure
1. Measure 2.82 g of potassium hydrogen tartrate in a clean, dry 150 mL beaker.
2. Dissolve the solid in 40 mL to 50 mL of pure water.
3. Transfer the solution into a 100 mL volumetric flask. Rinse the beaker and funnel two or three times with small quantities of pure water, transferring the rinsings into the
volumetric flask.
4. Add pure water, using a dropper and meniscus finder, to the flask until the volume is 100.0 mL.
5. Stopper the flask and mix the contents thoroughly by inverting the flask several times.
41. Potassium hydrogen tartrate (potassium bitartrate) is not considered a chemical hazard and therefore has no safety precautions for handling.
For sodium hydroxide, the precautions are: keep in a tightly closed container; protect from physical damage and store in a cool, dry, ventilated area away from sources of heat, moisture, and incompatibilities. Always add the caustic to water while stirring, never the reverse.
Containers of this material may be hazardous when empty since they retain product residues (dust, solids); observe all warnings and precautions listed for the product. Do not store with aluminium or magnesium. Do not mix with acids or organic material.
42. During a neutralization reaction between a strong acid and a strong base, the pH of the acid increases and the pH of the base decreases, whereas the pOH of the acid decreases and the pOH of the base increases. The final pH and pOH of the products of this reaction should all be exactly 7, as is always the case with strong acid–strong base neutralizations.
H3O+(aq) + OH–(aq) o 2 H2O(l) low pH high pH pH = 7 high pOH low pOH pOH = 7
43. Boric acid is a very weak acid, so that few of its molecules in solution react with water to produce hydronium ions.
<50%
H3BO3(aq) + H2O(l) o H3O+(aq) + H2BO3–(aq)
For strong acids such as HCl(aq), the dissolved molecules react with water almost completely, producing a high concentration of reactive hydronium ions.
>99%
HCl(aq) + H2O(l) o H3O+(aq) + Cl–(aq)
44. (a) HCN(aq) + H2O(l) o H3O+(aq) + CN–(aq) (b) HNO3(aq) + H2O(l) o H3O+(aq) + NO3–(aq) (c) NaNO2(aq) o Na+(aq) + NO2–(aq)
NO2–(aq) + H2O(l) o HNO2(aq) + OH–(aq) (d) Sr(OH)2(aq) o Sr2+(aq) + 2 OH–(aq) 45. (a) weak acid
(b) strong acid (c) weak base (d) strong base 46. Design
Obtain samples of each acid, along with a sample of pure water. Both acid samples should have the same amount concentration and all samples should have the same temperature.
Measure and record the pH of each sample. The acid with the lower pH value is the stronger acid, HNO3(aq). The manipulated variable is the type of acid used. The responding variable is the pH. The controlled variables are the concentration and temperature of the solutions. Water is the control.
Materials
Ɣ 100 mL samples of 0.10 mol/L nitric acid and nitrous acid at SATP Ɣ pH meter
Ɣ 3 - 150 mL beakers Ɣ pure water Ɣ baking soda Procedure
1. Using the pH meter, measure and record the pH of the sample of pure water.
2. Repeat step 1 for two samples of acid solution, remembering to rinse the electrodes after each measurement.
3. Dilute each sample with tap water, or neutralize each sample with baking soda before disposing of all samples down the drain.
Caution: Wear eye protection. Avoid eye and skin contact.
47. Ɣ Scientific perspective: Acid deposition is caused by oxides of sulfur and nitrogen that react with water in the atmosphere to produce acids. Research shows that the sources of these oxides are combustion products from automobiles, coal-burning power plants, and smelters.
Ɣ Ecological perspective: Acid deposition increases the acidity of lakes and streams, causing the depletion or destruction of wildlife populations. Acid deposition also adversely affects forests.
Ɣ Economic perspective: Acid deposition is endangering the fishing, tourism, agriculture, and forestry industries, leading to job loss and to rising social assistance costs.
Ɣ Political perspective: New legislation is limiting the production of sulfur and nitrogen oxides.
48. Materials
Ɣ eye protection Ɣ lab apron
Ɣ pure water wash bottle Ɣ centigram balance Ɣ 100 mL beaker Ɣ pH meter Ɣ stirring rod Ɣ solid glycolic acid
Ɣ 100 mL volumetric flask with stopper
Ɣ laboratory scoop Ɣ medicine dropper Ɣ meniscus finder Ɣ small funnel Procedure
1. (Prelab) Calculate the mass of glycolic acid required to prepare 100.0 mL of 1.00 mol/L solution.
2. Measure the required mass of solute in a clean, dry 100 mL beaker.
3. Pour approximately 50 mL of pure water into the beaker and stir until all of the solute has dissolved.
4. Carefully pour the solution of glycolic acid into the volumetric flask using a funnel.
Rinse all materials into the flask.
5. Add pure water to the flask, using the dropper and meniscus finder, until the volume is 100.0 mL.
6. Stopper the flask and invert several times to ensure complete dissolving.
7. Dry the beaker and add approximately 50 mL of solution to it.
8. Rinse the electrodes of a pH meter with distilled water. Measure and record the pH of the glycolic acid solution.
49. [H3O+(aq)] = 10–pH
= 10–1.92 mol/L
= 0.012 mol/L
50. CH2OHCOOH(aq) + H2O(l) o H3O+(aq) + CH2OHCOO–(aq) 51. [CH2OHCOOH(aq)] = 1.00 mol/L
[H3O+(aq)] = 1.00 mol/L 1
u 1 = 1.00 mol/L pH = –log[H3O+(aq)]
= –log(1.00 mol/L) = 0.000
If glycolic acid were a strong acid, its pH would be zero.
52. Glycolic acid might be preferred to hydrochloric acid because pure glycolic acid is a solid and easier to handle than either hydrogen chloride gas or a concentrated hydrochloric acid solution. Also, there are no fumes from a glycolic acid solution as there are from hydrochloric acid solutions.
53. NaHCO3(s) o Na+(aq) + HCO3–(aq)
HCO3–(aq) + H2O(l) o H2CO3(aq) + OH–(aq)
54. Uses of baking soda include: putting out grease or electrical fires; cleaning oil and grease stains; deodorizing; cleaning drains; using as underarm deodorant; brushing teeth; relieving discomfort of insect bites, rashes, and poison ivy; baking biscuits. Some uses that may involve acid-base reactions include: neutralizing spills of acids such as battery acid;
stabilizing pH in swimming pools; antacid for heartburn and acid indigestion.
55. An example might be the use of acidic cleaners to remove rust stains from plumbing fixtures.
The aesthetic benefit of shiny plumbing fixtures carries with it the risk of skin irritation or disfiguring other surfaces, resulting from careless use of the acidic cleaner. Also, disposal might be a problem if the cleaner is not greatly diluted. In this example, the risks may exceed the benefits if care is not taken.
The use of sodium hydroxide (pure solid or mixed with aluminium as in Drano) to clean clogged drains is an example of the risks likely exceeding the benefits. Solid drain cleaners are very corrosive and generate considerable heat. Risks include chemical burns to skin and/or eyes, and damage to plumbing or sinks. Much better alternatives exist, including
preventive measures by controlling what is put into the sink drain, cleaning with a mechanical snake (spring), or removing and cleaning the trap.
56. (a) CH3COOH(aq) + H2O(l) 50%o H3O+(aq) + CH3COO–(aq) (b) [H3O+(aq)] = 10–pH
= 10–2.4 mol/L = 4 u 10–3 mol/L
(c) The ratio of the solute (CH3COOH(aq)) to the hydronium ion concentration in the balanced chemical equation is 1:1. If acetic acid were a strong acid, the hydronium ion concentration would be 1 mol/L. Because the value calculated in (b) is not 1 mol/L, acetic acid must be a weak acid.
(d) Historically, vinegar has had a wide range of uses, from preserving food to cleaning wounds. Vinegar can be used to kill weeds, increase soil acidity, neutralize limestone, kill bacteria, remove odours, clean glass, deter pests (e.g., ants), clean rust from metals, and polish chrome.
57. The modern-day precursor to Aspirin was salicin, which is related to the active ingredient in Aspirin, acetylsalicylic acid. Aboriginal peoples used the bark of the white willow tree, in which this compound is present, to reduce pain, fever, and swelling. They would make a tea by boiling the bark in water, which released salicin.
58. (1) Solutions, acids and bases are differentiated by the type of solute (electrolyte, nonelectrolyte) and the type of solution (acidic, basic, neutral). Evidence for these
distinctions come from conductivity, acid-base indicators, and pH. Explanation of solutions came initially from the Arrhenius theory (in terms of dissociation and ionization) and was later refined into a modified Arrhenius theory (reaction with water) to incorporate hydronium ions and explanations of strong and weak acids and bases.
(2) Solutions are prevalent in nature such as lakes and oceans and also in all living organisms that contain and require water. Because solutions are so common and most are not neutral, it is important to know the properties and understand the types of solutions. In addition to natural examples, there are many technological examples such as the cooking process and cleaning materials. Knowledge of solutions is important for efficiency and safety.Extension Extension
59. Sulfuric acid is used in many industrial processes: as an electrolyte in many chemical cells, an ingredient in the manufacturing of nitroglycerine, a catalyst in many organic chemical and petrochemical processes, and in electroplating. The more such industries a country has, the higher its consumption of sulfuric acid. Therefore, the consumption of sulfuric acid can be directly related to the degree of a country’s industrialization.
60. This portrayal of acids is not accurate. The average person encounters many different acids daily without dangerous consequences. For example, boric acid is found in eyewash and glycolic acid is found in face creams. Many of the foods we eat are acidic. For example, oranges contain citric acid, cola pop contains phosphoric acid, and vinegar is a dilute solution of acetic acid. The reason these acids are not considered dangerous is because they are weak acids at low concentrations. Weak acids tend to have a higher pH because they do not react fully with water and only produce a limited concentration of hydronium ions when they dissolve. Weak acids, at sufficiently high concentrations, can be dangerous. The acids that are considered most dangerous, even at low concentrations, are the six strong acids, HClO4(aq), HCl(aq), HI(aq), HBr(aq), H2SO4(aq), and HNO3(aq), because of their corrosive properties.
The media could be more specific about the acids used, but most cases deal with fiction and perhaps viewers should be better educated.
61. Formic acid (methanoic acid) is the simplest carboxylic acid. Its chemical formula is CH2O2
or HCOOH. In nature, formic acid is found in the stings and bites of many insects, including bees and ants. It is also the principal irritant in the leaves of the stinging nettle. Formic acid is
used in the manufacturing of fumigants, animal feed additives, and commercial paint
strippers. The largest single use of formic acid is as a silage additive in Europe. It is used to a lesser extent in textile dyeing and finishing, leather tanning, nickel plating baths,
electroplating, coagulating rubber latex, regenerating old rubber, dehairing and plumping hides, and in the synthesis of Aspartame. Safety precautions: Do not breathe in vapour.
Keep away from heat and open flame. Store in a cool, dry place. Corrosive. Avoid prolonged exposure.
62. (a) Acute toxicity is studied by giving increasing doses of the chemical being tested to an organism until signs of toxicity become apparent. This process is usually gauged by observing the level of sickness or the death of the organism. The data gained from these tests are used to calculate the maximum tolerable dose, that is, the dose where signs of toxicity begin to occur. These data are then correlated to human usage of the chemical to determine the potential side effects and health hazards to humans.
(b) There is debate regarding animal testing – its moral implications weighed against the perceived benefits to humans. Advocates of animal testing argue that humans in some parts of the world experience better health largely due to advances in health and
manufacturing knowledge derived from animal testing. Animal-welfare and animal-rights advocates say that animal testing for commercial, non-medical substances is excessive and unnecessary, causing a great loss of animal life and inflicting suffering for the diminished pursuit of producing non-essential products, such as perfumes, cosmetics, and cleaning products. Animal-rights advocates argue that animal experiments infringe on the rights of animals and are never acceptable, even if they benefit humanity. The Aboriginal perspective is that all organisms on Earth have a purpose and that unnecessary suffering and death is unnatural and wrong.
There is also controversy about the scientific validity of animal experiments. Many doctors and scientists claim that they give misleading results that waste experimenters' time and result in unsafe drugs and products that harm humans. Many medical drugs have dangerous side effects that were not predicted by animal experiments. Animal-rights and animal-welfare supporters, scientists, doctors, and governments generally claim to agree that animal testing should cause as little suffering to animals as possible, and animal tests should be performed only when necessary.
