Chapter 15 Water and Aqueous Systems 15.2 Homogeneous Aqueous Systems 15.1 Water and Its Properties 15.2 Homogeneous Aqueous Systems 15.3 Heterogeneous Aqueous Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What types of substances dissolve most readily in water? Solutions Solutions What types of substances dissolve most readily in water? An aqueous solution is water that contains dissolved substances. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In a solution, the dissolving medium is the solvent. Solutions Solvents and Solutes In a solution, the dissolving medium is the solvent. The dissolved particles in a solution are the solute. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

A solvent dissolves the solute. Solutions Solvents and Solutes A solvent dissolves the solute. The solute becomes dispersed in the solvent. Solvents and solutes may be gases, liquids, or solids. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solutions are homogeneous mixtures. Solvents and Solutes Solutions are homogeneous mixtures. Solute particles can be atoms, ions, or molecules. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solutions Solvents and Solutes Substances that dissolve most readily in water include ionic compounds and polar covalent compounds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solutions Solvents and Solutes Substances that dissolve most readily in water include ionic compounds and polar covalent compounds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solutions The Solution Process Solvated ions Surface of ionic solid The process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called solvation. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solutions “Like dissolves like” Polar solvents such as water dissolve ionic compounds and polar compounds. Nonpolar solvents such as gasoline dissolve nonpolar compounds. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Which of these compounds should not dissolve in water? A. HCl B. C4H10 C. KI D. NH3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Which of these compounds should not dissolve in water? A. HCl B. C4H10 C. KI D. NH3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Why are all ionic compounds electrolytes? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Why are all ionic compounds electrolytes? An electrolyte is a compound that conducts an electric current when it is in an aqueous solution or in the molten state. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes All ionic compounds are electrolytes because they dissociate into ions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes To (+) electrode To (–) electrode Glucose, a nonelectrolyte, does not dissociate in water. A nonelectrolyte is a compound that does not conduct an electric current in either an aqueous solution or the molten state. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Some polar molecular compounds are nonelectrolytes in the pure state but become electrolytes when they dissolve in water. This change occurs because such compounds ionize in solution. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Some polar molecular compounds are nonelectrolytes in the pure state but become electrolytes when they dissolve in water. For example, ammonia (NH3(g)) is not an electrolyte in the pure state. Yet an aqueous solution of ammonia conducts an electric current because: NH3(g) + H2O(l)  NH4+(aq) + OH–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Not all electrolytes conduct electric current to the same degree. In a solution that contains a strong electrolyte, all or nearly all of the solute exists as ions. A weak electrolyte conducts an electric current poorly because only a fraction of the solute in the solution exists as ions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electrolytes and Nonelectrolytes Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells. An electrolyte imbalance can occur if you become dehydrated. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow? Electrolytes conduct an electric current when they are in an aqueous solution. Table salt, or NaCl, is a strong electrolyte. The water and salt in the pickle form a solution that conducts an electric current. The electric current causes the pickle to glow. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Explain why you must be extremely careful when using electricity near a swimming pool. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Explain why you must be extremely careful when using electricity near a swimming pool. The chlorinated water in a swimming pool is a solution that can conduct an electric current. If a current is introduced into the water, any swimmers could be shocked. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Why do hydrates easily lose and regain water? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates The water contained in a crystal is called the water of hydration or water of crystallization. A compound that contains water of hydration is called a hydrate. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. A substance that is anhydrous does not contain water. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CuSO45H2O(s) CuSO4(s) + 5H2O(g) Hydrates CuSO45H2O(s) CuSO4(s) + 5H2O(g) – heat + heat After a time, much of the blue hydrate has been converted to white anhydrous CuSO4. Heating of a sample of blue CuSO45H2O begins. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates Each hydrate contains a fixed quantity of water and has a definite composition. Some Common Hydrates Formula Chemical name Common name MgSO47H2O Magnesium sulfate heptahydrate Epsom salt Ba(OH)28H2O Barium hydroxide octahydrate CaCl22H2O Calcium chloride dihydrate CuSO45H2O Copper(II) sulfate pentahydrate Blue vitriol Na2SO410H2O Sodium sulfate decahydrate Glauber’s salt KAl(SO4)212H2O Potassium aluminum sulfate dodecahydrate Alum Na2B4O710H2O Sodium tetraborate decahydrate Borax FeSO47H2O Iron(II) sulfate heptahydrate Green vitriol H2SO4H2O Sulfuric acid hydrate (mp 8.6oC) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

To determine what percent by mass of a hydrate is water: Hydrates To determine what percent by mass of a hydrate is water: First determine the mass of water in one mole of hydrate. Then determine the molar mass of the hydrate. The percent by mass of water can be calculated using the following equation: Percent by mass H2O =  100% mass of water mass of hydrate Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Efflorescent Hydrates The water molecules in hydrates are held by weak forces, so hydrates often have an appreciable vapor pressure. If a hydrate has a vapor pressure higher than the pressure of water vapor in the air, the hydrate will lose its water of hydration, or effloresce. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates Hygroscopic Hydrates Hydrated ionic compounds that have low vapor pressure remove water from moist air to form higher hydrates. These hydrates and other compounds that remove moisture from air are called hygroscopic. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Hydrates Hygroscopic Hydrates Calcium chloride monohydrate spontaneously absorbs a second molecule of water when exposed to moist air. Calcium chloride is used as a desiccant in the laboratory. A desiccant is a substance used to absorb moisture from the air and create a dry atmosphere. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Finding the Percent by Mass of Water in a Hydrate Sample Problem 15.1 Finding the Percent by Mass of Water in a Hydrate Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate (Na2CO310H2O). Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Analyze List the known and the unknown. Sample Problem 15.1 Analyze List the known and the unknown. 1 KNOWN formula of hydrate = Na2CO310H2O UNKNOWN percent H2O = ? %

mass of 10 mol H2O = 10[(2  1.0 g) + 16.0 g] = 180.0 g Sample Problem 15.1 Calculate Solve for the unknown. 2 Determine the mass of 10 mol of water. mass of 10 mol H2O = 10[(2  1.0 g) + 16.0 g] = 180.0 g For every 1 mol of Na2CO310H2O, there are 10 mol of H2O. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Calculate Solve for the unknown. Sample Problem 15.1 Calculate Solve for the unknown. 2 Determine the mass of 1 mol of the hydrated compound. = (2  23.0 g) + 12.0 g + (3  16.0 g) + 180.0 g = 286.0 g molar mass of Na2CO310H2O Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Calculate Solve for the unknown. Sample Problem 15.1 Calculate Solve for the unknown. 2 Calculate the percent by mass of water in the hydrate. mass of water mass of hydrate percent by mass H2O =  100% 180.0 g 286.0 g =  100% = 62.94% Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Deliquescent Compounds Hydrates Deliquescent Compounds Some compounds are so hygroscopic that they become wet when exposed to normally moist air. These compounds are deliquescent, which means that they remove sufficient water from the air to dissolve completely and form solutions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Pellets of sodium hydroxide are deliquescent. Hydrates Pellets of sodium hydroxide are deliquescent. For this reason, containers of NaOH should always be tightly stoppered. The solution formed by a deliquescent substance has a lower vapor pressure than that of the water in the air. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O). Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O). mass of H2O = 7  ( 2  1.0 g + 16.0 g) = 126.0 g = 24.3 g + 32.1 g + (4  16.0 g) + 126.0 g = 246.4 g molar mass of MgSO47H2O 126.0 g 246.4 g percent by mass H2O =  100% = 51.14% Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

END OF 15.2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.