1. Most of the liquids that we encounter in the home are solutions. This could be tested by cooling, evaporating, orsmelling — anything that would encourage the components of a solution to separate.
2. Dissolving rate is usually speeded up by stirring, warming the solution, or finely dividing (grinding) the solute. Ifexcess solid remains after prolonged stirring, probably no more solute will dissolve.
3. Evidence for a reaction might be colour change, formation of a precipitate, formation of a gas, or a noticeable temper-ature change. The dissolving of both salt and sugar involves the solid separating into particles too small to see. Thisis a physical change. Like most physical changes, it is reversible: the water can be removed, leaving the solute in itsoriginal state.
Try This Activity: Measuring the Dissolving Process
(Page 313)
(a) The slightly cloudy mixture of table salt in water indicates that some substance(s) did not dissolve. Because we knowthat sodium chloride is soluble, table salt must be a mixture containing at least one low-solubility solid. The solutionof pickling salt was completely clear.
(b) The ingredients are salt, calcium silicate, potassium iodide, sodium thiosulfate (for Sifto brand). Calcium silicate islikely the cause of the cloudiness because silicates (such as sand) are not soluble in water.
(c) About 5 to 6 teaspoons of pickling salt appeared to dissolve.(d) The final volume is a little more than 100 mL, based on the approximate markings on the side of the Erlenmeyer flask.(e) The volume would likely be around 100 mL but not 120 mL, because solids generally dissolve in water without
increasing the volume. This can be tested by measuring 20.0 mL of sodium chloride in a graduated cylinder andadding this to 100.0 mL of water measured in another graduated cylinder.Note: The answer is about 106 mL.
7.1 SOLUBILITY
PRACTICE
(Page 316)
Understanding Concepts1. (a) About 20 g of K2SO4(s) will dissolve in 100 mL of water at 70°C.
(b) KNO3(s) and KCl(s) have equal solubilities at about 22°C.(c) To calculate molar concentration we would need to know the volume of the solution. The graph only gives the
volume of water used.(d) The only substance shown for which 100 g will dissolve in 100 mL of water is KNO3(s), at about 56°C.
2. (a) NaCl would precipitate first at temperatures above 31°C. (b) KCl would precipitate first at temperatures below 31°C.
Applying Inquiry Skills3. The graph created from Investigation 7.1.1 will normally differ somewhat from the one in Figure 2. The difference is
primarily experimental error, due to a less than precise design for the Investigation.
Try This Activity: Gas Solubility
(Page 317)
Some suggested answers are given.(a) The lit match is extinguished. This suggests the presence of carbon dioxide, which does not support combustion. (b) (Observations will vary depending on the relative humidity.) The air near the outside of the cold glass cools. As the
temperature of the air decreases, so does the solubility of water vapour in the air. Some water vapour condenses toliquid water. A qualitative test for water is to use cobalt(II) chloride paper.
(c) The small gas bubbles on the inside wall of the glass are likely due to air coming out of solution as the temperatureof the water increases to room temperature. As the temperature increases in the cold water glass, the volume of gasalso increases. In the hot water, the temperature is decreasing so the bubbles would stay small or decrease in volume.
PRACTICE
(Page 318)
Understanding Concepts4. A room temperature can of pop is more likely to spray: as gases are less soluble in warm liquids than in cold, the gases
will tend to come out of solution, so the pressure in the can is higher.
Reflecting5. (a) Red blood cells contain hemoglobin molecules, that bind chemically to oxygen molecules, making the oxygen
appear more soluble.(b) If blood held the same amount of oxygen as water, there would be only enough oxygen in our blood to keep our
cells alive for a few seconds, i.e., our lives would be different in the event of such a change by becoming dramat-ically shorter. To compensate, we would require completely different circulatory systems, for example, one thatsupplied a much greater volume of blood to our organs.
PRACTICE
(Page 319)
Understanding Concepts6. Temperature must always be stated when reporting a solubility.7.
8. (a) CO2(g) � H2O(l) → H2CO3(aq)
(b) H2CO3(aq) � Ca(OH)2(aq) → CaCO3(s) � 2 H2O(l)
(c) The second reaction can only occur if carbon dioxide is present for the first reaction, so the test is diagnostic.(d) If the calcium hydroxide solution were too dilute, the calcium carbonate that forms might be below its solubility,
and stay in solution rather than forming a precipitate. Thus, the test would not work.(e)
0 20 40
Solubility Curve for Calcium Hydroxide
Temperature (°C)
Sol
ubili
ty (
g/1
00 m
L)
60 80 100
0.05
0.10
0.15
0.20
Temperature
Solids
Gases
Sol
ubili
ty
(f) From the solubility curve drawn in (e), the solubility of Ca(OH)2(s) at 22°C is 0.17 g/100 mL, or 0.17 g/0.100 L. v Ca(OH)2
� 1.0 L
c Ca(OH)2 � 0.17 g/100 mL � 0.17 g/0.100 L
m Ca(OH)2 � 1.0 L� � �
00.1.1070
gL�
�
m Ca(OH)2� 1.7 g
The minimum mass of calcium hydroxide required to make up 1 L of saturated solution will be about 1.7 g. The actualmass one would use should be much more than this — say, 15 to 20 g, to ensure a large excess of solute, which inturn ensures saturation.
Note: In this particular instance the volume of the solute added is very small compared to the volume of thesolvent; so the difference between solvent volume and solution volume may be considered negligible.
(g) The solubility of calcium hydroxide is anomalous — unlike most solids it decreases in solubility with increasingtemperature. The generalization we use is still valid and useful for most soluble solids. It just needs to be under-stood that generalizations are exactly that — statements that generally (not invariably) describe events correctly.
Applying Inquiry Skills
9. Prediction (a) The solubility of potassium chlorate should increase with an increase in temperature, according to the general-
ization for the solubility of solids, and also according to Figure 2 on page 316 of the text.Analysis(b)
(c) According to the Evidence, the solubility of potassium chlorate increases with increasing temperature, for solu-tion temperatures from 0°C to 100°C.
Making Connections10. Gases such as oxygen are less soluble in warm water, so active fish that require high oxygen levels may not thrive in
water that is warmed by an outside source, such as a power plant. In addition, power plants may alter the ecology ofa body of water by preventing it from freezing over in the winter. This would attract waterfowl that would feed onaquatic organisms normally under the ice at this time.
PRACTICE
(Page 325)
Understanding Concepts11. (a) The high/low solubility cutoff point is 0.10 mol/L at SATP.
(b) The 0.10 mol/L cutoff is useful because most laboratory solutions are within an order of magnitude of thisconcentration, and because most ionic solids are either markedly more or less soluble than this value.
(c) The table need only be used to determine the solubility of an ionic solid if the solid does not contain a group Iion, an ammonium ion, or a nitrate ion — because such compounds are always highly soluble. To determine thesolubility of any other ionic solid, find the anion in its column heading, and look down the column to find the row
containing the cation. The row where the cation is found will identify the compound as having low or high solu-bility.
(d) In chemistry class, the word soluble usually refers to compounds that the table classes as “high solubility.” Theword insoluble usually refers to the compounds that the table classes as “low solubility,” provided their solubilityis so low that no effect is noticed from dissolving.
12. (a) NaOH(s) high solubility(b) MnCl2(s) high solubility(c) Al(OH)3(s) low solubility(d) Ca3(PO4)2(s) low solubility(e) CuSO4�5H2O(s) high solubility
13. (a) Large crystals take more time to “grow,” so the sugar probably crystallized slowly from a saturated solution.(b) Solubility is not affected by crystal size, so the specialty sugar would have the same solubility as regular white
sugar.(c) The dissolving rate is slower for large crystals.
Applying Inquiry Skills
14. Experimental DesignSmall quantities of a solid may be dissolved sequentially in a measured sample of a solute until no more will dissolve,to determine the solubility; or a saturated solution of known volume can be evaporated to dryness, and the solubilitycalculated from the measured mass of solid solute remaining.
Making Connections15. Pollutants in natural water can enter the water cycle through runoff from agricultural areas or landfills, or industrial
tailings ponds. Some pollutants are toxic and/or noxious at extremely low concentrations, so they may be dangerouseven if they have very low solubility.
PRACTICE
(Page 326)
Understanding Concepts16.
Making Connections17. In the Solvay process, the scientific knowledge of solubility effects made possible a new technique for producing a
commercial chemical much more efficiently — a classic example of science leading technology.
SECTION 7.1 QUESTIONS
(Page 326)
Understanding Concepts1. (a) The presence of the solid is evidence that sodium bromide is precipitating, probably because the solvent is evap-
orating (or maybe because of a drop in temperature). The solution is therefore at the limit of its concentration forthis temperature.
(b) The concentration of sodium bromide in the remaining solution is at the maximum possible value. Such a solu-tion is said to be saturated.
Solubility Curves
Temperature
Sol
ubili
ty
NaHCO3
NH4HCO3
(c) The mixture could be converted to a single phase solution by adding more solvent, or by warming. Either processwould dissolve the solid present.
2. Solids generally become more soluble as temperature increases, while gases generally become less soluble as temper-ature increases.
Applying Inquiry Skills
3. Prediction(a) Barium sulfate should become more soluble as temperature increases, according to the generalization about the
solubility of ionic solids.
Experimental Design(b) The independent variable is the solution temperature. The dependent variable is the mass of barium sulfate. The
most important controlled variable is the volume of saturated solution taken each time.
Analysis(c)
(d) According to the evidence from this investigation, barium sulfate does become more soluble as temperatureincreases.
Evaluation(e) The experiment could be improved by just making and using a single saturated solution, and taking samples from
it at different temperatures.(f) The prediction was verified, according to the evidence gathered.(g) The solubility generalization is supported by the results of this experiment. One test of one compound is certainly
not enough evidence to justify stating such a generalization. Many repeated tests of many compounds would berequired for scientific acceptance and confidence.
Making Connections4. If a non-aqueous solvent is used, it is probably because the dirt and grease on clothing dissolves better in such
solvents. Also, some clothing fabrics are damaged by water, but are not affected by non-aqueous solvents.5. (a) Cold, fast-flowing streams will have a higher concentration of dissolved oxygen, because more air will be mixed
with turbulent water, and because gases dissolve better in colder water.(b) Trout probably require more oxygen than carp.(c) Thermal pollution would probably affect trout seriously, because warming their water will reduce its oxygen
concentration.
7.2 HARD WATER TREATMENT
PRACTICE
(Page 329)
Understanding Concepts1. (a) Scale in kettles and soap scum are both evidence of hard water.
(b) Ground water is hard in areas where soluble calcium and magnesium minerals exist in the ground.
(c) The mixture could be converted to a single phase solution by adding more solvent, or by warming. Either processwould dissolve the solid present.
2. Solids generally become more soluble as temperature increases, while gases generally become less soluble as temper-ature increases.
Applying Inquiry Skills
3. Prediction(a) Barium sulfate should become more soluble as temperature increases, according to the generalization about the
solubility of ionic solids.
Experimental Design(b) The independent variable is the solution temperature. The dependent variable is the mass of barium sulfate. The
most important controlled variable is the volume of saturated solution taken each time.
Analysis(c)
(d) According to the evidence from this investigation, barium sulfate does become more soluble as temperatureincreases.
Evaluation(e) The experiment could be improved by just making and using a single saturated solution, and taking samples from
it at different temperatures.(f) The prediction was verified, according to the evidence gathered.(g) The solubility generalization is supported by the results of this experiment. One test of one compound is certainly
not enough evidence to justify stating such a generalization. Many repeated tests of many compounds would berequired for scientific acceptance and confidence.
Making Connections4. If a non-aqueous solvent is used, it is probably because the dirt and grease on clothing dissolves better in such
solvents. Also, some clothing fabrics are damaged by water, but are not affected by non-aqueous solvents.5. (a) Cold, fast-flowing streams will have a higher concentration of dissolved oxygen, because more air will be mixed
with turbulent water, and because gases dissolve better in colder water.(b) Trout probably require more oxygen than carp.(c) Thermal pollution would probably affect trout seriously, because warming their water will reduce its oxygen
concentration.
7.2 HARD WATER TREATMENT
PRACTICE
(Page 329)
Understanding Concepts1. (a) Scale in kettles and soap scum are both evidence of hard water.
(b) Ground water is hard in areas where soluble calcium and magnesium minerals exist in the ground.
2. (a) Na2CO3(s) and Ca(OH)2(s)(b) The added carbonate ions cause calcium and magnesium ions in the hard water to precipitate, because CaCO3
and MgCO3 have very low solubility.
3. (a) C CaCO3� 7.1 � 10-5 mol/L
MCaCO3� 100.09 g/mol
c CaCO3� �
0.0000L71 mol�� � �
10m0.0
o9l�
g�
c CaCO3� 0.0071 g/L � 7.1 mg/L
The concentration of calcium carbonate in the treated water will be equal to the solubility; 7.1 mg/L.
(b) 7.1 mg/L is equal to 7.1 ppm.(c) The treated water is classified as soft, according to Table 1.
4. A home water softener unit has to be regenerated because the resin in it has a finite capacity to attract hard water ions,to replace sodium ions. The sodium ions go into the bath and washing machine, but no precipitate (bathtub ring)forms. When no more Ca2+
(aq) and Mg2+(aq) ions can attach to the resin, the regeneration cycle replaces the hard water ions
with fresh sodium ions. The hard water ions are flushed down the drain.
Making Connections5. On a large scale, the amount of resin required for softening would be extremely expensive, and the volume of concen-
trated brine needed for regeneration would be enormous, and thus a problem to make and store. The quantity ofsodium and chloride ions in the water might pose a health problem for some people.
6. Detergents clean well in harder water, producing no “soap scum,” which was a huge benefit. However, they increasedsome pollution problems. Early detergents were not very biodegradable, and phosphates from detergents created (andsometimes still do create) eutrophication problems in lakes and rivers.
7. Home-softened water (from ion-exchange softeners) is often not routed to toilets (for economy), and sometimes notto a kitchen tap that provides drinking water (for possible health reasons). The incidence of heart disease is statisti-cally slightly lower in areas with hard water than in areas with naturally soft water. People with heart concerns, partic-ularly those on low-sodium diets, may not wish to drink home-softened water (which is often high in sodium).
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SECTION 7.2 QUESTIONS
(Page 330)
Understanding Concepts1. Water is naturally hard in areas where ground water comes in contact with minerals (such as limestone) that contain
(aq) and Mg2+(aq) are the ions mostly responsible for water hardness.
3. (a) Laundry “scum” and kettle scale are the noticeable effects of hard water.(b) One serious effect of hard water that is not readily noticeable is the formation of scale in pipes. If it is allowed to
build up unchecked, the scale can significantly reduce the flow of water through the pipe, and come close toblocking it completely.
5. (a) Calcium ions are more readily attracted than sodium ions to negatively charged sulfonate sites on a resin mole-cule. This is mostly because a calcium ion has a charge of 2+, twice as much as the charge of a sodium ion.
(b) During regeneration, there are very many more sodium ions present (at maximum concentration) than calciumions, so the chance that sodium ions will collide with and attach to the sulfonate sites becomes very much greater,overcoming the fact that calcium ions are attracted more strongly than sodium ions.
Applying Inquiry Skills
6. Question(a) Is water softened by passing through a pipe to which a magnet is attached?
Experimental DesignHard water is run through a pipe to a tap, and samples are tested for hardness, with and without a magnet beingattached to the pipe.
(b) EvaluationThe original design is obviously useless in light of the new understanding of the claim made for the magnet; it isnot testing the claimed result.
New Experimental DesignHard water is run through identical piping that has and has not magnets attached. After several months, the piping iscut and the ease of removing the scaling from the inside of the pipe is determined.
4. (a) Compounds could be any four of:copper(II) nitrate, copper(II) sulfate, copper(II) acetate, copper(II) chloride, copper(II) bromide,or copper(II) iodide.
or (if the oxalate ion formula is written in condensed form)
Ca2+(aq) � C2O2–
4(aq) → CaC2O4(s)
7. Pb(s) � 2 Ag+(aq) → Pb2+
(aq) � 2 Ag(s)
Making Connections8. (a) Fe3+
(aq) � 3 OH–(aq) → Fe(OH)3(s)
(b) Filtration to remove the precipitate is the most likely process.
Explore an Issue
Debate: Producing Photographs
(Page 336)
(a) At first glance, it seems that digital cameras are more environmentally friendly than film cameras: they don’t requirefilm, film canisters, developing paper, or processing chemicals. However, this conclusion is based upon the assump-tion that only the final products affect the environment.
(b) To argue against the proposition you need to recognize that the whole story of a product must be considered, includingeverything from the extracting of resources to manufacturing through disposal. For example, are there components ofthe digital camera that during manufacture cause the emission of toxins into the environment, or, when the cameramust be disposed of, are there environmental concerns?
(c) Recognize that the resolution requires an environmental perspective only; you need not consider, for example,economic, social, and technological arguments. In your investigation, you could look at subtopics such as raw mate-rials, manufacturing, the developing process, the developing technology (and its environmental impact back to itsorigins), and disposal.
(d) Consider the logic of the presentation and the quantity of evidence used to support the position taken. Were all stagesfrom pre-manufacturing through post-disposal considered?
SECTION 7.3 QUESTIONS
(Page 336)
Understanding Concepts1. Pb2+
(aq) � SiO2–3(aq) → PbSiO3(s)
2. 3 Ca2+(aq) � 2 PO3–
4(aq) → Ca3(PO4)2(s)
3. Cu(s) � 2 Ag+(aq) → Cu2+
(aq) � 2 Ag(s)
Making Connections4. Student answers will vary widely, as they will be specific to the regulations controlling local hazardous waste
facilities.
GO TO www.science.nelson.com, Chemistry 11, Teacher Centre.
7.4 WASTE WATER TREATMENT
PRACTICE
(Page 340)
Understanding Concepts1. Problems from the release of untreated sewage include: transmission of disease, lowering of oxygen levels, and rapid
growth of aquatic plant life.2. A high BOD reading is an indication that bacteria are using up oxygen to decompose organic material in the water.
This is a problem for any oxygen-using life form in the water.
3.
4. Material that flows into a rural septic system is generally removed only by bacterial decomposition. Ideally, only waterand biodegradable substances should be flushed. Homeowners should be careful not to overwhelm the decompositionprocess by flushing large quantities of any pollutants.
Reflecting5. What goes down our drains is likely to end up in the ground or surface water. Being careful about waste disposal at
home and at school can make a cumulative positive difference in the quality of our environment.
SECTION 7.4 QUESTIONS
(Page 340)
Understanding Concepts1.
Applying Inquiry Skills
2. (a) Hypotheses(1) The fish kill may be due to a lack of oxygen caused by sewage discharge of organic matter into the river.
or(2) The fish kill may be due to discharge of toxic material or a disease-causing organism into the river.
(b) Prediction (1)The fish kill is caused by a high BOD, due to excess discharge of organic matter in sewage upstream.
deliver to user
postchlorination
ammoniation
primary treatment:screening, flotation,settling, and filtration
Experimental Design (1)The water is tested for oxygen and for organic matter, every 500 m upstream from the fish-kill area to the industrialtown.
Prediction (2)The fish kill is caused by toxic chemicals or disease organisms in the sewage discharge upstream.
Experimental Design (2)The water is tested for chemicals and for organisms causing common diseases in fish, every 500 m upstream from thefish-kill area to the industrial town.
Note: This is an example of a correlational study (see Appendix A1, pages 608 – 9). Technically, correlationalstudies are inductive investigations without a hypothesis and a prediction. Note above that when forced, a hypothesisand a prediction are similar, indicating that the investigation is inductive and that neither a hypothesis nor a predic-tion should be used.
Making Connections3. Garbage disposal units decrease the amount of solid bagged waste from a household, which cuts costs and extends the
usefulness of landfills. However, the increase of organic matter in the sewage places more demand on the local wastewater treatment system. Most of this food waste could be diverted to a composting system.
4. Answers will depend on the regulations controlling local hazardous waste facilities. Unless the local area has a tertiarytreatment facility, there will automatically be an argument for improvement. The only logical long-term human goalis to eventually have all waste water returned to the cycle in a form that puts no stress on the environment.
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7.5 QUALITATIVE CHEMICAL ANALYSIS
PRACTICE
(Page 342)
Understanding Concepts1. (a) colourless
(b) blue(c) yellow-brown(d) orange(e) colourless(f) green
3. (a) yellow-red (b) light blue-grey(c) bright red(d) green
Applying Inquiry Skills
4. (a) AnalysisAccording to Table 2, Colours of Flames:solution A contains K+ ions,solution B contains Cu2+ ions,solution C contains Na+ ions,solution D contains Ca2+ ions, and solution E contains Li+ ions and/or Sr2+ ions.
(b) EvaluationThe design of this experiment is too limited. It only identifies those positive ions (cations) in the solutions that
happen to produce coloured flames. Other possible cations, not to mention the anions in each of these solutions,cannot be identified this way. As well, solution E may contain either or both of two cations, since they bothproduce the same result.
PRACTICE
(Page 346)
Understanding Concepts5. Qualitative analysis determines what is in a sample, and quantitative analysis determines how much is present.6. A diagnostic test statement always includes procedure, evidence, and analysis steps. For example: If a gas is bubbled
through limewater, and a white precipitate forms, then the gas is likely to contain carbon dioxide.7. Precipitates could be formed with the listed ions by adding:
Applying Inquiry Skills8. (a) To precipitate carbonate ions from a sample, without at the same time precipitating sulfide ions, add a compound
that supplies any Group II cation, and an anion that is always soluble in combination (e.g., calcium nitrate, bariumnitrate, or magnesium nitrate).
(b) One example: Ca2+(aq) � CO2–
3(aq) → CaCO3(s)
9. Experimental DesignCalcium nitrate solution is added to the test solution sample. If a precipitate forms it is filtered, and silver nitrate solu-tion is added to the filtrate (or to the original sample, if no precipitate formed in the initial test).
Making Connections10. There are innumerable examples of qualitative analysis in society. Common examples include environmental tests for
lead (or other heavy metals) in water supply systems; continuous monitoring by household detectors (carbonmonoxide or natural gas in houses, propane in trailers); simple swimming pool or aquarium water-testing kits(including quantitative analysis); or even home pregnancy tests. There are also hundreds of industrial and commercialexamples of qualitative analysis. There are many career opportunities as an analyst.
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SECTION 7.5 QUESTIONS
(Page 346)
Understanding Concepts1. The precipitation reactions are:
3. (a) Calcium (yellow-red flame test) can be distinguished from the other ions by a flame test, but lithium and stron-tium both give bright red flame tests, and so cannot be distinguished from each other in this way.
(b) Adding sulfate (or carbonate, phosphate, or sulfite) ions to the two unidentified test solutions (aqueous sodiumsulfate, for instance) would precipitate the strontium ions, but not the lithium ions.
Applying Inquiry Skills
4. (a) Experimental DesignThe solution is flame tested.
(b) EvaluationThe experimental design is seriously flawed, because both ions produce coloured flames. If the initial flame testis bright red, there is no way to know whether potassium ions are present, because the violet colour will be hiddenby the strontium ion colour.
Alternative answer:
(a) Experimental DesignSodium sulfate is added to the solution. Any precipitate is filtered and then the filtrate or original solution is flametested.
(b) EvaluationThe experimental design is not valid. Although you will know with certainty whether strontium ions are presentor not, based upon whether a precipitate forms or not, you will not be able to determine whether potassium ionsare present, due to the masking of the potassium flame colour by the sodium flame colour. If cobalt-blue glass isemployed in the materials and the procedure, then the design would be valid. (The cobalt-blue glass filters theyellow sodium colour from the flame and allows one to determine whether potassium is present or not.)Alternately, the cation for the sodium solution must be chosen to have a colourless flame test, e.g., hydrogen.(Unfortunately, a list of colourless flame-test ions is not provided in the text and would have to be researched.)
5. Experimental DesignSodium chloride solution is added to the sample. If a precipitate forms, it is filtered. Sodium hydroxide solution isadded to the filtrate (or sample, if no precipitate forms). If a precipitate forms, it is filtered. Sodium carbonate (orsulfate) solution is added to the filtrate (or sample, if no precipitate forms).
Note: A precipitate in the initial step (when you use any soluble halide ion compound) indicates that thallium ionsare present. A precipitate in the second step (when you use any soluble hydroxide compound) indicates that calciumions are present. A precipitate in the third step (when you use any soluble sulfate, carbonate, phosphate, or sulfitecompound) indicates that barium ions are present. The sequence of steps is very important: sodium carbonate cannotbe added first, for example.
6. (a) The Experimental Design is satisfactory. The solution colour test can confirm the presence of copper(II) ions, butnot calcium ions; and any red in the flame test will confirm the presence of calcium ions.
(b) Alternative Experimental DesignSodium sulfate solution is added to the sample solution. If a precipitate forms, it is filtered. Sodium carbonatesolution is added to the filtrate (or sample, if no precipitate forms).Note: A precipitate in the initial step (when you use any soluble sulfate compound) indicates that calcium ions
are present. A precipitate in the second step (when you use any soluble sulfide, carbonate, phosphate, or sulfitecompound) indicates that copper(II) ions are present.
7. Any carbonated beverage is a home solution with a gaseous solute. A diagnostic test is: If a gas is bubbled throughlimewater, and a white precipitate forms, then the gas contains carbon dioxide.
Another example would be household ammonia, or any of several spray window cleaners containing ammonia. Thediagnostic test would be the characteristic odour of ammonia.
8. Sodium carbonate is a typical home solution with a solid solute; e.g., as a water softener (washing soda) in laundrydetergents. Diagnostic tests for this example would be flame testing for sodium ions, and precipitation using calciumchloride solution, for carbonate ions.
9. Experimental DesignOxalic acid is added to sample solutions of nitrate or chloride compounds of as many metal cations as can be foundin the school laboratory supplies. Any precipitate formation is recorded.
10. Experimental DesignA solution of the product is first flame tested; then a solution of calcium chloride is added.
Note: A yellow flame test indicates sodium; a precipitate indicates carbonate ions.
Making Connections11. Forensic chemists analyze tissue for many things. A typical test would be for the presence and amount of arsenic.
Quantity must be measured precisely to determine if a substance is present in a natural amount, or in an amount muchgreater, which could perhaps indicate foul play.
GO TO www.science.nelson.com, Chemistry 11, Teacher Centre.
According to the stoichiometric method, the mass of zinc hydroxide produced is predicted to be 2.49 g.Note: The calculated answer of 2.485 g can be rounded to 2.48 g or 2.49, depending on the rounding rule used
in the classroom.
(b) AnalysismZn(OH)2
� 3.30 g � 0.91 g � 2.39 g
According to the evidence, the mass of zinc hydroxide that is actually produced is 2.39 g.
(c) Evaluationdifference � 2.39 g � 2.48 g � 0.10 g
% difference � �02..1408
g�g�
� � 100% � 3.8%
Note: The unrounded value of 2.485 g was used in the calculation. If the rounded value is used, the differenceis 0.09 g and the percentage difference is 3.6%.
The prediction was 3.8% higher than the value obtained, and so is judged to be verified by the experimental results.A prediction within 5% is considered acceptably accurate (95% accurate) for this kind of lab work, with any differ-ence probably just due to normal experimental error.(d) The stoichiometric concept is supported by the results of this investigation, and judged to be acceptable because
the prediction was verified. There is good confidence in this judgment, and no need is seen to modify the concept.
SECTION 7.6 QUESTIONS
(Page 355)
Applying Inquiry Skills1. Precipitating all the lead(II) ions will require adding an excess of a solution containing an anion (in this case, sulfate)
that forms a low-solubility compound with lead(II). Making a sodium sulfate solution is a logical choice, since sodiumsulfate is soluble, inexpensive, and easy to obtain.First, the mass of sodium sulfate required must be calculated.Pb(NO3)2(aq) � Na2SO4(aq) → PbSO4(s) � 2 NaNO3(aq)
2.0 L m
0.34 mol/L 142.04 g/mol
n Pb(NO3)2= 2.0 L� � �
0.314
L�mol� � 0.68 mol
n Na2SO4= 0.68 mol � �
11
� � 0.68 mol
m Na2SO4= 0.68 mol�� �
1412m.0
o4l�g
�
m Na2SO4= 97 g
orm Na2SO4
= �0.3
1
4
L�m
P
o
b
l�(
P
N
b
O
(N
3)
O
2�3)2�
� � �1
1
m
m
ol�o
P
l�b
N
(
a
N2
O
SO
3)�4�
2���
14
1
2.
m
04
ol�g
N
N
a
a
2
2
S
S
O
O
4�4�
m Na2SO4= 97 g
A minimum mass of 97 g of sodium sulfate must be used.
To ensure a complete precipitation of lead(II) ions, using an excess of sodium sulfate will be necessary. Commonlythis amount should be about 10% more than the minimum required — say, 105 g of sodium sulfate, in this case.
The simplest process would be to obtain 105 g of sodium sulfate and dissolve it to make, say, 1.0 L of reacting solu-tion. It is possible that not all of the solute will dissolve, depending on the water temperature. This problem could besolved by increasing the solvent volume.
2. The experimental design is judged to be inadequate, because the mass of solid measured includes not only the precip-itate but also the excess reactant and the second (soluble) product. The latter two chemicals crystallize out of the solu-tion when the water is boiled away. The mass of solid remaining will be of more than one substance, with no way tocalculate amounts from the value. The precipitate should have been separated by filtration and then dried.
If we take the reaction in Question 3 as an example, precipitating and then crystallizing would result in a mixture ofthe solids, aluminum nitrate (the excess reactant), aluminum sulfide (the precipitate), and sodium nitrate (the second(but soluble) product).
According to the stoichiometric method, the mass of aluminum sulfide produced is predicted to be 0.210 g.
(b) Analysism Al2S3
� 1.17 g � 0.97 g � 0.20 g
According to the evidence, the mass of aluminum sulfide that is actually produced is 0.20 g.
(c) EvaluationThe design of the experiment is judged to be adequate, with no obvious flaws. It allowed the question to beanswered easily with simple materials, concepts, and procedures.difference � 0.20 g � 0.210 g � 0.01 g
% difference � �0
0
.
.
2
0
1
1
0
g�g�� � 100% � 5%
The prediction was 5% higher than the value obtained, and is judged to be verified by the experimental results. Aprediction within 5% is considered acceptably accurate (95% + ...) for this kind of lab work, with any difference prob-ably just due to normal experimental error.
The stoichiometric concept is the authority for this investigation. It is supported by the results of this investigation,and judged to be acceptable because the prediction was verified. There is good confidence in this judgment, and thereis no need to modify the concept.
4. (a) Analysisv AgNO3
= 100 mL = 0.100 Lm AgNO3
= 6.74 g � 1.27 g � 5.47 gM AgNO3
= 169.88 g/mol
nAgNO3= 5.47 g� � �
1619m.8
o8lg�
�
� 0.0322 mol
CAgNO3= �
0.00.312020
mL
ol�
CAgNO3= 0.322 mol/L
The molar concentration of silver nitrate in solution is 0.322 mol/L.
Making Connections5. The most common way to check the concentration of antifreeze is to measure its density, since density and concen-
tration are proportional. Battery acid is measured the same way (to determine battery charge). The higher the concen-tration of solute, the denser the solution will be, and the higher in the solution a buoyant object will float. A calibrateddevice used to measure liquid density in this way is called a hydrometer. Common density units for solutions are g/mLand kg/L, but concentrations of automotive fluids are usually expressed in terms of what they are intended to do:lowest working temperature (for antifreeze), or charge condition (for battery acid). It is also common to state solutiondensities as a ratio with the density of pure water — giving a numerical value greater or less than 1 — called the“specific gravity” of the solution.
GO TO www.science.nelson.com, Chemistry 11, Teacher Centre.
Understanding Concepts1. Combinations (a), (b), (c), (d), and (f) will react, but only (a), (c), (d), and (f) will form precipitates. The reaction equa-
tions are:(a) Cu2+
(aq) + 2 OH–(aq) → Cu(OH)2(s)
(b) H+(aq) + H–
(aq) → H2O(l)
(c) 3 Ca2+(aq) + 2 PO3–
4(aq) → Ca3(PO4)2(s)
(d) Ag+(aq) + Cl–(aq) → AgCl(s)
(f) Cu+(aq) � Cl–(aq) → CuCl(s)
2. (a) Zn2+(aq) + CO2–
3(aq) → ZnCO3(s)
(b) Pb2+(aq) + CO2–
3(aq) → PbCO3(s)
(c) 2 Fe3+(aq) + 3 CO2–
3(aq) → Fe2(CO3)3(s)
(d) Cu2+(aq) + CO2–
3(aq) → CuCO3(s)
(e) Ag+(aq) + CO2–
3(aq) → Ag2CO3(s)
(f) Ni2+(aq) + CO2–
3(aq) → NiCO3(s)
(g) The choice of sodium carbonate is good because carbonate ions form low soluble compounds with most metallicions and the compound is soluble, common, and inexpensive.
3. (a) Al3+(aq) + 3 OH–
(aq) → Al(OH)3(s)
and Ca2+(aq) + SO2–
4(aq) → CaSO4(s)
or 2 Al3+(aq) + 3 SO2–
4(aq) + 3 Ca2+(aq) + 6 OH–
(aq) → 2 Al(OH)3(s) + 3 CaSO4(s)
Note: The effective precipitate for clarifying the water is the flocculent precipitate, Al(OH)3(s).
(b) 3 Ca2+(aq) + 2 PO3–
4(aq) → Ca3(PO4)2(s)
(c) Mg2+(aq) + 2 OH–
(aq) → Mg(OH)2(s)
(d) Fe3+(aq) + 3 OH–
(aq) → Fe(OH)3(s)
4. Cu2+(aq)
5. Ions of alkali metals, as well as hydrogen, ammonium, and nitrate ions, form compounds with high solubility.6. A violet flame indicates potassium ions. A precipitate with Hg+
(aq) could indicate any anion on the solubility chartexcept sulfate, nitrate, or acetate. The compound in solution might be KCl, KBr, K2S, K2SO4, KOH, K3PO4, or ...
7. In aqueous solution:(a) Cu+ is green, Cu2+ is blue.
The minimum volume of sodium carbonate solution required is 0.318 L.(b) A suitable volume would be about 350 mL. (Assume an excess of � 10%.)
10. The mass of zinc reacted (24.89 g � 21.62 g) � 3.27 gZn(s) � 2 HCl(aq) → ZnCl2(aq) � H2(g)
3.27 g 350 mL 350 mL
65.38 g/mol C
nZn � 3.27 g� � �615.
m38
olg�
�
nZn � 0.0500 mol
nZnCl2� 0.0500 mol � �
11
� � 0.0500 mol
CZnCl2� �
0.00.530500
mL
ol�
CZnCl2� 0.143 mol/L
or
CZnCl2� 3.27 g� Zn� � �
6
1
5.
m
38
ol�g�Z
Z
n�n�
� � �1
1
m
m
ol
o
Z
l�n
Z
C
n�l2� � �
0.35
1
0 L�
CZnCl2� 0.143 mol/L
The molar concentration of zinc chloride solution is 0.143 mol/L.
Applying Inquiry Skills11. The precipitated anion could be SO4
2–, CO32–, PO4
3–, or SO32–.
Since most sulfates are soluble, and most sulfites, carbonates, and phosphates are only slightly soluble, the originalsolution could be tested with Zn(NO3)2(aq), Cu(NO3)2(aq), or Ni(NO3)2(aq), etc. If no precipitate forms, the anion mustbe SO4
2–.
12. Experimental DesignThe solution is tested with TlNO3(aq) (or Hg2(NO3)2(aq) or CuNO3(aq)) for the presence of halide ions. If a precipitateforms it is filtered, and the filtrate (or original solution if no precipitate forms) is tested with Ca(NO3)2(aq) (or barium,strontium, or radium nitrate) for the presence of sulfate ions.
13. Experimental DesignThe solutions are tested with litmus to identify the acid and hydroxide (basic) compounds. The remaining solutionsare then tested for conductivity (to identify the ionic compound). To confirm that the final solution contains nitrogengas, it could be heated slightly. The formation of tiny bubbles would confirm the presence of a dissolved gas.
Note: The least confidence is for the nitrogen test. Nitrogen has one-half the solubility of oxygen gas in water —0.00175 g/100 mL.
(b) Analysismass of PbCl2 (s) precipitate (4.58 g – 0.91 g) = 3.67 g
Pb(NO3)2(aq) + 2 NaCl(aq) → PbCl2 (s) � 2 NaNO3(aq)
50.0 mL 3.67 g
C 278.10 g/mol
n PbCl2= 3.67 g� � �
2718m.1
o0lg�
� = 0.0132 mol
n NaCl = 0.0132 mol � �21
� = 0.0264 mol
C NaCl = �00.0.0256040mLol
�
C NaCl = 0.528 mol/L
or
C NaCl � 3.67 g� PbCl2� ��27
1
8
m
.1
o
0
l�g�Pb
P
C
bC
l�2
l�2�� �
1
2
m
m
o
o
l�l
P
N
b
a
C
C
l�l
2� � �
0.05
1
00 L�
C NaCl = 0.528 mol/L
According to the evidence and the stoichiometric concept, the concentration of sodium chloride in the seawater sample is0.528 mol/L.
(c) EvaluationThe design of this experiment is judged to be adequate because it allowed the question to be answered easily, andwith confidence in the result. There are no apparent flaws and the equipment is simple and easy to use.
15. (a) Materials• CuSO4(aq) sample solution
• 0.750 mol/L NaOH (aq) stock solution
• medicine dropper
• 25-mL pipet and bulb
• 250-mL beaker
• 400-mL beaker
• filtration apparatus
• filter paper
• wash bottle of pure water
• centigram balance
(b) Analysismass of Cu(OH)2 (s) precipitate (2.83 g – 0.88 g) = 1.95 g
CuSO4(aq) + 2 NaOH(aq) →Cu(OH)2 (s) � 2 Na2SO4(aq)
25.0 mL 1.95 g
C 97.57 g/mol
nCu(OH)2= 1.95 g� � �
917.
m57
olg�
� = 0.0200 mol
nCuSO4= 0.0200 mol � �
11
� = 0.0200 mol
CCuSO4= �
00..002205000
mLol
�
CCuSO4= 0.799 mol/L
or
CCuSO4� 1.95 g� Cu(OH)2� � �
9
1
7.
m
57
ol�g�C
C
u
u
(O
(O
H
H
)�)�2
2� � �
1
1
m
m
o
o
l�l
C
C
u
u
(O
SO
H4
)� 2�
CCuSO4= 0.799 mol/L
According to the evidence and the stoichiometric concept, the concentration of copper(II) sulfate in the sample is0.799 mol/L.
(c) EvaluationThe design of this experiment is judged to be adequate because it allowed the question to be answered easily, andwith confidence in the result. There are no apparent flaws and the equipment is simple and easy to use.
Making Connections16. For example, the hardness may be 250 ppm (250 mg/L). The soda-lime process could be used by adding washing soda,
Na2CO3(aq), and lime, Ca(OH)2(aq)/(s), to the water to precipitate the hard-water ions as carbonates; e.g., CaCO3(s).Note: Answers will be specific to school/community location.
GO TO www.science.nelson.com, Chemistry 11, Teacher Centre.
17. Answers will vary, but might express concern about an old septic system at a cottage because of a danger of leakage,which might release disease-causing organisms into ground water.
Note: Answers will be specific to school/community location. Student discussion should use concepts from thischapter.
GO TO www.science.nelson.com, Chemistry 11, Teacher Centre.
18. (a) Recall that ppm = mg/L
O2(aq) (maximum) in 50 L is:
50 L� � �14.7
L�mg� � 735 mg at 0°C
and
50 L� � �8.7
L�mg� � 435 mg at 20°C
735 � 435 mg � 300 mg
The difference in mass of oxygen that can be dissolved in 50 L of water at the two temperatures is 300 mg.(b) Fish require O2 for respiration, so they might prefer 0°C water, in which O2 solubility is higher and obtaining
sufficient oxygen would be easier. On the other hand, the temperature of the surrounding water affects the activitylevel of cold-blooded animals. The fish would not be able to move as fast at the colder temperature.
