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15.2 Homogeneous Aqueous Systems > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 15 Water and Aqueous Systems.

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Presentation on theme: "15.2 Homogeneous Aqueous Systems > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 15 Water and Aqueous Systems."— Presentation transcript:

1 15.2 Homogeneous Aqueous Systems > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 15 Water and Aqueous Systems 15.1 Water and Its Properties 15.2 Homogeneous Aqueous Systems 15.3 Heterogeneous Aqueous Systems

2 15.2 Homogeneous Aqueous Systems > 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Although it sounds absurd, an ordinary dill pickle from the deli can be a source of light when connected to an electric current! CHEMISTRY & YOU How can you make a pickle glow?

3 15.2 Homogeneous Aqueous Systems > 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Solutions What types of substances dissolve most readily in water?

4 15.2 Homogeneous Aqueous Systems > 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Solutions What types of substances dissolve most readily in water? An aqueous solution is water that contains dissolved substances.

5 15.2 Homogeneous Aqueous Systems > 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Solvents and Solutes In a solution, the dissolving medium is the solvent. The dissolved particles in a solution are the solute.

6 15.2 Homogeneous Aqueous Systems > 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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.

7 15.2 Homogeneous Aqueous Systems > 7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Solvents and Solutes Solutions are homogeneous mixtures. Solute particles can be atoms, ions, or molecules. If you filter a solution through filter paper, both the solute and solvent pass through the filter.

8 15.2 Homogeneous Aqueous Systems > 8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Substances that dissolve most readily in water include ionic compounds and polar covalent compounds. Solvents and Solutes

9 15.2 Homogeneous Aqueous Systems > 9 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions Substances that dissolve most readily in water include ionic compounds and polar covalent compounds. Nonpolar covalent compounds, such as methane, and compounds found in oil, grease, and gasoline, do not dissolve in water. However, oil and grease will dissolve in gasoline. Solvents and Solutes

10 15.2 Homogeneous Aqueous Systems > 10 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions The Solution Process A water molecule is polar, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. As individual solute ions break away from the crystal, the negatively and positively charged ions become surrounded by solvent molecules and the ionic crystal dissolves.

11 15.2 Homogeneous Aqueous Systems > 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions The process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called solvation. Solvated ions Surface of ionic solid The Solution Process

12 15.2 Homogeneous Aqueous Systems > 12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Solutions The Solution Process Polar solvents such as water dissolve ionic compounds and polar compounds. Nonpolar solvents such as gasoline dissolve nonpolar compounds. This relationship can be summed up in the expression “like dissolves like.”

13 15.2 Homogeneous Aqueous Systems > 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Which of these compounds should not dissolve in water? A.HCl B.C 4 H 10 C.KI D.NH 3

14 15.2 Homogeneous Aqueous Systems > 14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Which of these compounds should not dissolve in water? A.HCl B.C 4 H 10 C.KI D.NH 3

15 15.2 Homogeneous Aqueous Systems > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electrolytes and Nonelectrolytes Why are all ionic compounds electrolytes?

16 15.2 Homogeneous Aqueous Systems > 16 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.

17 15.2 Homogeneous Aqueous Systems > 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electrolytes and Nonelectrolytes All ionic compounds are electrolytes because they dissociate into ions.

18 15.2 Homogeneous Aqueous Systems > 18 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electrolytes and Nonelectrolytes In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution. Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water. To (+) electrode To (–) electrode

19 15.2 Homogeneous Aqueous Systems > 19 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electrolytes and Nonelectrolytes Mercury(II) chloride, a weak electrolyte, is only partially dissociated in water. To (+) electrode To (–) electrode In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution.

20 15.2 Homogeneous Aqueous Systems > 20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Electrolytes and Nonelectrolytes 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. To (+) electrode To (–) electrode In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution.

21 15.2 Homogeneous Aqueous Systems > 21 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.

22 15.2 Homogeneous Aqueous Systems > 22 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 (NH 3 (g)) is not an electrolyte in the pure state. Yet an aqueous solution of ammonia conducts an electric current because ammonium ions (NH 4 + ) and hydroxide ions (OH – ) form when ammonia dissolves in water. NH 3 (g) + H 2 O(l)  NH 4 + (aq) + OH – (aq)

23 15.2 Homogeneous Aqueous Systems > 23 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.

24 15.2 Homogeneous Aqueous Systems > 24 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. When you exercise, you can lose water and electrolytes from your body through perspiration.

25 15.2 Homogeneous Aqueous Systems > 25 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?

26 15.2 Homogeneous Aqueous Systems > 26 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. CHEMISTRY & YOU Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow?

27 15.2 Homogeneous Aqueous Systems > 27 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Explain why you must be extremely careful when using electricity near a swimming pool.

28 15.2 Homogeneous Aqueous Systems > 28 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.

29 15.2 Homogeneous Aqueous Systems > 29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Hydrates Why do hydrates easily lose and regain water?

30 15.2 Homogeneous Aqueous Systems > 30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The water contained in a crystal is called the water of hydration or water of crystallization. Hydrates A compound that contains water of hydration is called a hydrate.

31 15.2 Homogeneous Aqueous Systems > 31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. Hydrates

32 15.2 Homogeneous Aqueous Systems > 32 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. Hydrates A substance that is anhydrous does not contain water.

33 15.2 Homogeneous Aqueous Systems > 33 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Heating of a sample of blue CuSO 4  5H 2 O begins. After a time, much of the blue hydrate has been converted to white anhydrous CuSO 4. CuSO 4  5H 2 O(s) CuSO 4 (s) + 5H 2 O(g) – heat + heat

34 15.2 Homogeneous Aqueous Systems > 34 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates 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 CoCl 2 ). When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl 2  6H 2 O).

35 15.2 Homogeneous Aqueous Systems > 35 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Each hydrate contains a fixed quantity of water and has a definite composition. Hydrates Some Common Hydrates FormulaChemical nameCommon name MgSO 4  7H 2 OMagnesium sulfate heptahydrateEpsom salt Ba(OH) 2  8H 2 OBarium hydroxide octahydrate CaCl 2  2H 2 OCalcium chloride dihydrate CuSO 4  5H 2 OCopper(II) sulfate pentahydrateBlue vitriol Na 2 SO 4  10H 2 OSodium sulfate decahydrateGlauber’s salt KAl(SO 4 ) 2  12H 2 O Potassium aluminum sulfate dodecahydrate Alum Na 2 B 4 O 7  10H 2 OSodium tetraborate decahydrateBorax FeSO 4  7H 2 OIron(II) sulfate heptahydrateGreen vitriol H 2 SO 4  H 2 OSulfuric acid hydrate (mp 8.6 o C)

36 15.2 Homogeneous Aqueous Systems > 36 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Percent by mass H 2 O =  100% mass of water mass of hydrate 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:

37 15.2 Homogeneous Aqueous Systems > 37 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Efflorescent Hydrates 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. The water molecules in hydrates are held by weak forces, so hydrates often have an appreciable vapor pressure.

38 15.2 Homogeneous Aqueous Systems > 38 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Hygroscopic Hydrates These hydrates and other compounds that remove moisture from air are called hygroscopic. Hydrated ionic compounds that have low vapor pressure remove water from moist air to form higher hydrates.

39 15.2 Homogeneous Aqueous Systems > 39 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Hygroscopic Hydrates 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. Calcium chloride monohydrate spontaneously absorbs a second molecule of water when exposed to moist air.

40 15.2 Homogeneous Aqueous Systems > 40 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate (Na 2 CO 3  10H 2 O). Sample Problem 15.1 Finding the Percent by Mass of Water in a Hydrate

41 15.2 Homogeneous Aqueous Systems > 41 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. KNOWN formula of hydrate = Na 2 CO 3  10H 2 O UNKNOWN percent H 2 O = ? % Analyze List the known and the unknown. 1 Sample Problem 15.1 To determine the percent by mass, divide the mass of water in one mole of the hydrate by the molar mass of the hydrate and multiply by 100%.

42 15.2 Homogeneous Aqueous Systems > 42 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Determine the mass of 10 mol of water. Calculate Solve for the unknown. 2 For every 1 mol of Na 2 CO 3  10H 2 O, there are 10 mol of H 2 O. Sample Problem 15.1 mass of 10 mol H 2 O = 10[(2  1.0 g) g] = g

43 15.2 Homogeneous Aqueous Systems > 43 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Determine the mass of 1 mol of the hydrated compound. Calculate Solve for the unknown. 2 Sample Problem 15.1 = (2  23.0 g) g + (3  16.0 g) g = g molar mass of Na 2 CO 3  10H 2 O

44 15.2 Homogeneous Aqueous Systems > 44 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the percent by mass of water in the hydrate. Calculate Solve for the unknown. 2 Sample Problem 15.1 mass of water mass of hydrate percent by mass H 2 O =  100% = 62.94% g g =  100%

45 15.2 Homogeneous Aqueous Systems > 45 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The mass of the water accounts for more than half the molar mass of the compound. So, a percentage greater than 50% is expected. Evaluate Does the result make sense? 3 Sample Problem 15.1

46 15.2 Homogeneous Aqueous Systems > 46 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Hydrates Deliquescent Compounds These compounds are deliquescent, which means that they remove sufficient water from the air to dissolve completely and form solutions. Some compounds are so hygroscopic that they become wet when exposed to normally moist air.

47 15.2 Homogeneous Aqueous Systems > 47 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. Hydrates

48 15.2 Homogeneous Aqueous Systems > 48 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO 4  7H 2 O).

49 15.2 Homogeneous Aqueous Systems > 49 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO 4  7H 2 O). = 24.3 g g + (4  16.0 g) g = g molar mass of MgSO 4  7H 2 O mass of H 2 O = 7  ( 2  1.0 g g) = g g g percent by mass H 2 O =  100% = 51.14%

50 15.2 Homogeneous Aqueous Systems > 50 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Key Concepts and Key Equation Substances that dissolve most readily in water include ionic compounds and polar covalent compounds. All ionic compounds are electrolytes because they dissociate into ions. The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained. mass of water mass of hydrate percent by mass H 2 O =  100%

51 15.2 Homogeneous Aqueous Systems > 51 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms aqueous solution: water that contains dissolved substances solvent: the dissolving medium in a solution solute: dissolved particles in a solution solvation: a process that occurs when an ionic solute dissolves; in solution, solvent molecules surround the positive and negative ions

52 15.2 Homogeneous Aqueous Systems > 52 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms electrolyte: a compound that conducts an electric current when it is in an aqueous solution or in the molten state; all ionic compounds are electrolytes, but most covalent compounds are not nonelectrolyte: a compound that does not conduct an electric current in aqueous solution or in the molten state strong electrolyte: a solution in which a large portion of the solute exists as ions weak electrolyte: a solution that conducts electricity poorly because only a fraction of the solute exists as ions

53 15.2 Homogeneous Aqueous Systems > 53 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms water of hydration: water molecules that are an integral part of a crystal structure hydrate: a compound that has a specific number of water molecules bound to each formula unit anhydrous: a substance that does not contain water effloresce: to lose water of hydration; the process occurs when the hydrate has a vapor pressure higher than that of water vapor in the air

54 15.2 Homogeneous Aqueous Systems > 54 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Glossary Terms hygroscopic: a term describing salts and other compounds that remove moisture from the air desiccant: a hygroscopic substance used as a drying agent deliquescent: describes a substance that removes sufficient water from the air to form a solution; the solution formed has a lower vapor pressure than that of the water in the air

55 15.2 Homogeneous Aqueous Systems > 55 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Ionic compounds and polar covalent compounds dissolve most readily in water to form aqueous solutions. Ionic compounds dissolve in water when the polar water molecules attract the ions of the solute, causing the individual solute ions to break away from the ionic crystal. BIG IDEA Bonding and Interactions

56 15.2 Homogeneous Aqueous Systems > 56 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. END OF 15.2


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