UNIT 4: Solutions and Solubility

Chapter 8: Solutions and Their Properties Chapter 9: Reactions in Aqueous Solutions How are qualitative analysis and quantitative analysis used to describe the composition of a solution, and how do humans use and affect the world’s water supply? Chapter 10: Acids and Bases UNIT 4: Solutions and Solubility

UNIT 4 Chapter 9: Reactions in Aqueous Solutions All forms of life have one thing in common – water. Water’s ability to dissolve many different compounds enables it to carry the nutrients required by the vast range of life forms on Earth. However, water can also dissolve and carry harmful compounds, both natural substances and human-made pollutants. Chapter 9: Reactions in Aqueous Solutions

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 The reaction shown here is a double displacement reaction with a spectacular colour change. In water, ionic substances dissociate into their component ions. Non-reacting ions in an aqueous solution are called spectator ions. Note that water is not a reactant in the chemical equation. 9.1 Net Ionic Equations and Qualitative Analysis

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 In an ionic equation, the formulas of soluble ionic compounds are replaced with the formulas of the ions that these compounds form in water. The following equation: 2AgNO3(aq) + Na2CrO4(aq)  Ag2CrO4(s) + 2NaNO3(aq) becomes: 2Ag+(aq) + 2NO3-(aq) + 2Na+(aq)+CrO42-(aq)  Ag2CrO4(s) + 2Na+(aq) + 2NO3-(aq) when the formulas for ionic substances are written in dissociated form. Writing Ionic Equations

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Spectator ions will appear on both sides of the equation and can be canceled to obtain the net ionic equation. This equation shows only the ions that react. 2Ag+(aq)+CrO42-(aq)  Ag2CrO4(s) It is convenient to use this form of the equation since the source of the silver and chromate ions does not matter. Changing the spectator ions does not change the reaction. Writing Net Ionic Equations Spectators are present at a sporting event but do not take part in the event, just as spectator ions are present in a reaction but do not take part in it.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Rules for Writing a Net Ionic Equation

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Qualitative analysis identifies elements, ions, or compounds in a sample. To identify certain ions, you can observe the: Qualitative Analysis • colour in a flame test • colour of a solution • formation of a precipitate Fireworks are a spectacular demonstration of the different colours of light that are given off by metal ions when they are heated.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Since many metal ions produce a distinct colour when heated, a flame test (described below) can help identify metal ions. A Bunsen burner and a clean wire loop are used to test an aqueous solution (dip the loop) or a solid (moisten the loop with HCl(aq)). The substance is placed on the loop and then into the flame. Electrons in the atoms of the sample absorb energy from the flame, and some of the energy as visible light. Flame Tests These photographs show flame tests of strontium and copper. Notice that the colour of the copper flame is greener than a typical Bunsen burner flame.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Flame Tests

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Aqueous solutions of ionic compounds of certain cations and anions have characteristic colours. Colours of Ions in Solution

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Another way to identify an unknown ion in a solution is to add a known reactant to the solution and observe whether or not a precipitate forms. The solubility guidelines can be used to infer which ion must have been present in the unknown solution. This can be done multiple times to the same solution to further identify ions in the filtrate. Formation of a Precipitate

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Formation of a Precipitate

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.1 Section 9.1 Review

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.2 Solution stoichiometry is often used in quantitative analysis, which involves determining a quantity (how much) of a substance is present in a sample. In solution stoichiometry, known volumes and concentrations of reactants or products are used to determine the volumes, concentrations, or masses of other reactants or products. 9.2 Solution Stoichiometry Accurate measurement is important in both cooking and chemistry. A cake made from improperly measured ingredients may not look good and may not taste good either!

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.2 Rules for Solving Solution Stoichiometry Problems

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.2 Example Given: Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) Volume of AgNO3 solution = 100 mL Mass of dried Ag(s) precipitate = 1.65 g What is the molar concentration of silver nitrate solution? Solution Stoichiometry Problem Solving

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.2 1. Calculate the amount in moles of Ag(s): n(Ag) = 1.65 g × 1 mol = 0.015 296 mol 107.87 g 2. Use moles of Ag to calculate moles of AgNO3: n =AgNO3= 2 mol AgNO3 × 0.0015 296 mol Ag 2 mol = 0.015296 mol AgNO3 3. Calculate the concentration of AgNO3: c = 0.015 296 mol = 0.153 mol/L 0.100 L Solution Stoichiometry Problem Solving

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.2 The limiting reactant is usually the one that is the most expensive. This is one way to keep the costs in industrial chemical processes as low as possible. These calculations are much like those in Chapter 7. The amount in moles of a solution is determined using n = c × V. Limiting Reactant Problems

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 The figure below illustrates the fact that a very small amount (0.01%) of Earth’s water, found in lakes and rivers as surface water, is available for safe human use. The salt water in the oceans makes up 97.5% of the total amount of water, and most of the fresh water is unavailable in ground water (0.74%) far below Earth’s surface or is frozen in polar ice caps (1.75%). 9.3 Water Quality Very little of the water on Earth is fresh water, and very little fresh water is available for people to drink.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Water quality is affected by: Harmful Substances • naturally occurring substances, some of which are harmful • pollutants that originate from human activities • water treatment standards The quality of any water depends on factors that are not always immediately visible.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Ionic Compounds Containing Arsenic Naturally Occurring Harmful Substances • found in ground water beneath river deltas; more serious in countries such as Bangladesh • most ground water in Canada has less than 5 ppb, considered to be the safe level • long-term exposure to dangerous levels of these compounds may lead to cancer and diabetes • Fluoride Ions • less than 1 ppb is considered safe and actually • beneficial to strengthen tooth enamel Fluoride ions prevent tooth decay, but too much fluoride can cause brown stains on teeth.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Calcium and Magnesium Ions Naturally Occurring Harmful Substances • high levels of calcium and magnesium ions make the water hard,which leads to formation of insoluble soap scum as well as a buildup of lime (calcium carbonate) deposits in pipes and appliances Many of the rocks in southern Ontario are limestone, which makes most of the water in this region hard. The lime scale in this water pipe was caused by hard water.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Twotypes: Pollutants from Human Activity • Point Source of Pollution: a single source with a specific location • Example: wrecked tanker leaking oil • Non-point Source of Pollution: no easily defined location and may involve many substances spread over large areas • Example: fertilizers used on farms (A) Point source of pollution: Waste water from a factory can quickly pollute a body of water. (B) Non-point source of pollution: Run-off from farms can carry fertilizer and pesticides into nearby waterways.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Lead Compounds The Ontario government introduced the Cosmetic Pesticide Act in 2009 to protect the environment by lowering or banning the use of harmful garden and lawn pesticides. Despite these initiatives, pollutants such as lead, mercury, nitrates, and phosphates are still a major problem. Lead is released by industrial processes such as ore smelting, car battery production, and plastics production. While environmental lead pollution has decreased significantly, exposure is still occurring and can lead to kidney failure, nerve damage, and brain disorders.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Mercury Compounds Much of the mercury deposited in the Great Lakes comes from emissions from coal-fired power plants, gold mines, cement plants, and smelters. Mercury is highly toxic; it affects the central nervous system, producing tremors, irritability, numbness, and tunnel vision.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Nitrate and Phosphate Ions The source of these ions comes mainly from livestock waste and fertilizer use. These ions may leach into lakes and rivers, where they promote plant and algal growth (blooms). The bacteria that decompose this algal growth absorb the available oxygen, leaving the fish populations starved of oxygen. Nitrate and phosphate pollution can cause excessive plant growth in lakes and rivers.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Although algal blooms appear to help plant growth at first, the overall environmental effect is negative because of the loss of both plant and animal life.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Infants less than three months old are susceptible to high concentrations of nitrate ions in the water. Nitrate ions are converted to nitrite ions in an infant’s digestive tract. These ions bond to the hemoglobin, leading to a condition known as blue-baby syndrome.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Airborne Pollution Non-metallic oxides such as carbon dioxide, sulfur dioxide, and nitrogen oxide gases dissolve in rainwater and contribute to acid rain. Sources of these pollutants include motor vehicles, refineries, and many factories. Acid rain leaches aluminum ions into ground water and surface water, which can harm aquatic life considerably.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Pollutants from Human Activity Plastic Leachates Water bottles and other hard plastic containers contain polycarbonates. Polycarbonates are made using the chemical bisphenol A (BPA). This substance can leach into the liquid inside the plastic container. Recently BPA has been linked to breast cancer, heart disease, and other biological changes such as those caused by the hormone estrogen. Although banned from baby bottles, BPA is still found in food containers and continues to leach into the environment from landfills.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Water Quality and Drinking Water Standards In North America, various treatment plants ensure that our drinking water is clear, colourless, tasteless, and odourless and is free of disease-causing organisms and unsafe levels of toxic compounds. Ontario has maximum allowable concentration (MAC) standards for selected ions and compounds in drinking water.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.3 Maximum Concentrations of Selected Ions and Compounds in Ontario’s Drinking Water

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Serious consequences result when water is polluted and then not treated properly to make it safe to drink. Here are a few examples: 9.4 Water Treatment • May 2000: A well for the town of Walkerton was contaminated by run-off from a nearby farm. This run-off contained E. coli bacteria from animal manure and was not tested or processed properly. Seven people died, and thousands became seriously ill.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Polluted Water • 1962: Reed International in Dryden, Ontario began using mercury in a process to make bleaching chemicals for its pulp and paper plant. The mercury waste water was dumped into the river. Mercury compounds accumulated in local fish, which were eaten by local residents. Residents became sick with mercury poisoning, and, to this day, newborns still show clear signs of mercury poisoning. Between 1962 and 1970, Reed International dumped over 9000 kg of mercury into the Wabigoon-English River system.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Treatment: Temporary Hardness Hard water contains dissolved calcium (and magnesium) carbonates. CaCO3(s) + H2O(ℓ) + CO2(aq) + Ca(HCO3)2(aq) Calcium hydrogen carbonate Ca(HCO3)2(aq) and the comparable magnesium compound are the main causes of temporary hardness. Boiling removes carbon dioxide from the solution, so it is not available to react to make calcium hydrogen carbonate. However, the calcium carbonate precipitates out of the solution and deposits on the heating appliance. Deposits of calcium carbonate and magnesium carbonate on water-heating elements can reduce the heater’s efficiency.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Treatment: Permanent Hardness Permanent water hardness is caused by dissolved calcium (and magnesium) sulfate. This hardness cannot be removed by boiling but must be treated by chemical methods. One way is to add sodium carbonate, Na2CO3•10H2O (washing soda) as a water softener. This precipitates the calcium (and magnesium) carbonates out of solution. CaSO4(aq) + Na2CO3(s)  CaCO3(s) + Na2SO4(aq) This treatment makes the water basic. Use of an ion-exchange water softener avoids this problem.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Treatment: Ion-Exchange Water Softeners Water softened by an ion-exchange softener contains a high concentration of sodium ions. People on a low-sodium diet should avoid drinking water from a sodium ion water softener.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Treatment: Desalination The process of obtaining fresh water from salt water is called desalination. Once it is safe to drink, the water is called potable water. Desalination plants are commonly used in the Middle East where oil is a cheap fuel used to heat the ocean water. The salt-free water vapour is condensed and collected. The Jubail desalination plant, on the Arabian Gulf in Saudi Arabia, is the largest desalination plant in the world. Some of the energy that is needed to boil the water comes from waste heat from an adjacent electrical power plant.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Reverse osmosis is a more energy-efficient method for making potable water. Water Treatment: Reverse Osmosis • Osmosis is the tendency of a solvent to move through a semi-permeable membrane to make the concentrations of solutes on both sides of the membrane equal. • Therefore, water will flow from the more dilute side into the more concentrated side. • In reverse osmosis, high pressure is applied to the more concentrated side to force water through the membrane in the reverse-of-the-normal direction.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Treatment Reverse Osmosis Desalination Plants Large reverse osmosis desalination plants are built in coastal areas. The largest in North America is in Tampa Bay, Florida. It produces 100 million litres of potable water daily. High pressure forces water across a semi-permeable membrane inside these vessels. The water that passes through the membranes is completely free of salt and other ions.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Water Supply Treatment As shown in the graph, life expectancy has increased dramatically since around 1800. Many health scientists have concluded that this is due mostly to the widespread improvement in the quality of water supplies around that time. Life expectancy in North America has increased steadily since 1800, partly because of improvements in water treatment.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Municipal Water Treatment Municipalities use a combination of physical and chemical processes to purify water.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Waste-Water Treatment The goal of waste-water treatment is to remove solids, chemicals, and dangerous bacteria from sewage. The water can then be released into the environment. Waste-water treatment plants remove possible pollutants from sewage so that those pollutants cannot enter and harm the environment.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Stages in Waste-Water Treatment • Primary Treatment in holding tanks removes solid materials by sedimentation and by skimming scum from the surface of the water. The addition of calcium hydroxide and aluminum sulfate promotes formation of aluminum hydroxide precipitate. • Secondary Treatment uses natural micro-organisms that feed on organic matter in the sewage. These bacteria convert organic material into carbon dioxide, water, and nitrogen compounds. • Tertiary Treatment involves chemical precipitation of nitrogen, phosphorus, and organic compounds.

UNIT 4 Chapter 9: Reactions in Aqueous Solutions Section 9.4 Stages in Waste-Water Treatment

UNIT 4: Solutions and Solubility