4/9/14 15.2 Homogeneous Aqueous Systems > 15.2 Homogeneous Aqueous Systems > CHEMISTRY & YOU How can you make a pickle glow? Although it sounds absurd, an ordinary dill pickle from the deli can be a source of light when connected to an electric current! Chapter 15 Water and Aqueous Systems 15.1 Water and Its Properties 15.2 Homogeneous Aqueous Systems 15.3 Heterogeneous Aqueous Systems 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Solutions 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Solutions Solutions Solvents and Solutes What types of substances dissolve most readily in water? • In a solution, the dissolving medium is the solvent. • The dissolved particles in a solution are the solute. • An aqueous solution is water that contains dissolved substances. • Solvents and solutes may be gases, liquids, or solids. 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 1 4/9/14 15.2 Homogeneous Aqueous Systems > Solutions 15.2 Homogeneous Aqueous Systems > Solutions Solvents and Solutes Solvents and Solutes Substances that dissolve most readily in water include • Solutions are homogeneous mixtures. • Solute particles can be atoms, ions, or molecules. ionic compounds and • Cannot separate solutions through filtering 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Solutions polar covalent compounds. 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Solutions The Solution Process Solvation: the process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called. Solvents and Solutes • Methane, oils, grease, and gasoline, do not dissolve in water. • However, oil and grease will dissolve in gasoline. Nonpolar Solvated ions “like dissolves like” Surface of ionic solid 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 2 4/9/14 15.2 Homogeneous Aqueous Systems > 15.2 Homogeneous Aqueous Systems > Which of these compounds should not dissolve in water? 9 Which of these compounds should not dissolve in water? A. HCl A. HCl B. C4H10 B. C4H10 C. KI C. KI D. NH3 D. NH3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Electrolytes and Nonelectrolytes 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Electrolytes and Nonelectrolytes electric current must flow between the two electrodes Electrolytes and Nonelectrolytes All ionic compounds are electrolytes • Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water. • Good conductors • conducts an electric current when it is in an aqueous solution or in the molten state. • Dissociate into ions To (+) electrode 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 12 To (–) electrode Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 3 4/9/14 15.2 Homogeneous Aqueous Systems > Electrolytes and Nonelectrolytes 15.2 Homogeneous Aqueous Systems > • Mercury(II) chloride, a weak electrolyte, is only partially dissociated in water. • Weak conductors • Glucose, is a nonelectrolyte (does not dissociate in water). To (+) electrode 13 To (–) electrode Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Electrolytes and Nonelectrolytes To (+) electrode 14 Electrolytes and Nonelectrolytes Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells. • Perspiration NH3(g) + H2O(l) à NH4+(aq) + OH–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. To (–) electrode Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Some polar molecular compounds are nonelectrolytes in the pure state but become electrolytes when they dissolve in water. Ionization 15 Electrolytes and Nonelectrolytes • Dehydration 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4 4/9/14 15.2 Homogeneous Aqueous Systems > CHEMISTRY & YOU 15.2 Homogeneous Aqueous Systems > How can you make a pickle glow? Explain why you must be extremely careful when using electricity near a swimming pool. Although it sounds absurd, an ordinary dill pickle from the deli can be a source of light when connected to an electric current! 17 The chlorinated water in a swimming pool is a solution that can conduct an electric current. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Hydrates 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. 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Hydrates CuSO45H2O(s) Copper (II) sulfate pentahydrate + heat – heat CuSO4(s) + 5H2O(g) anhydrous CuSO4. • Water in hydrates is weakly attached to the crystal, therefore easily removed. • A substance that is anhydrous does not contain water. 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 5 4/9/14 15.2 Homogeneous Aqueous Systems > Hydrates 15.2 Homogeneous Aqueous Systems > Hydrates Each hydrate contains a fixed quantity of water and has a definite composition. • A piece of filter paper that has been dipped in an aqueous solution of cobalt(II) chloride and then dried is blue in color (anhydrous CoCl2). • When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl26H2O). 21 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Hydrates Some Common Hydrates 22 Common name MgSO47H2O Magnesium sulfate heptahydrate Epsom salt Ba(OH)28H2O Barium hydroxide octahydrate CaCl22H2O Calcium chloride dihydrate CuSO45H2O Copper(II) sulfate pentahydrate Blue vitriol Na2SO410H2O Sodium sulfate decahydrate Glauber’s salt KAl(SO4)212H2O Potassium aluminum sulfate dodecahydrate Alum Na2B4O710H2O Sodium tetraborate decahydrate Borax FeSO47H2O Iron(II) sulfate heptahydrate Green vitriol H2SO4H2O Sulfuric acid hydrate (mp 8.6oC) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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 (Na2CO310H2O). mass of water Percent by mass H2O = mass of hydrate x 100% Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chemical name 15.2 Homogeneous Aqueous Systems > To determine what percent by mass of a hydrate is water: 23 Formula 24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 6 4/9/14 15.2 Homogeneous Aqueous Systems > Sample Problem 15.1 15.2 Homogeneous Aqueous Systems > 2 Calculate Solve for the unknown. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O). Calculate the percent by mass of water in the hydrate. mass of water percent by mass H2O = mass of hydrate x 100% 180.0 g = 286.0 g x 100% = 62.94% 25 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Hydrates Efflorescent Hydrates H2O in hydrates - held by weak forces Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O). so hydrates often have an appreciable vapor pressure. mass of H2O = 7 x ( 2 x 1.0 g + 16.0 g) = 126.0 g • Vapor pressure hydrate > vapor pressure air • effloresce. molar mass of = 24.3 g + 32.1 g + (4 x 16.0 g) + 126.0 g MgSO47H2O = 246.4 g 126.0 g percent by mass H2O = 246.4 g x 100% = 51.14% 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 7 4/9/14 15.2 Homogeneous Aqueous Systems > Hydrates 15.2 Homogeneous Aqueous Systems > Hydrates Hygroscopic Hydrates Hygroscopic Hydrates Vapor pressure hydrate < vapor pressure air • Desiccant : compound used to absorb moisture from the air and create a dry atmosphere. • Compounds that remove moisture from air are called hygroscopic. 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 15.2 Homogeneous Aqueous Systems > Hydrates Deliquescent Compounds Beyond hygroscopic… • Deliquescent: remove sufficient water from the air to dissolve completely and form solutions. 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 8
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