HC CH 15 sec 2 - Eastern Regional High Schoolweb.eccrsd.us/borda/public/honors/HC_CH15_2.pdf ·...
Transcript of HC CH 15 sec 2 - Eastern Regional High Schoolweb.eccrsd.us/borda/public/honors/HC_CH15_2.pdf ·...
4/9/14
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
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?
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?
• An aqueous solution is water that contains dissolved substances.
15.2 Homogeneous Aqueous Systems >
4 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.
• Solvents and solutes may be gases, liquids, or solids.
4/9/14
2
15.2 Homogeneous Aqueous Systems >
5 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.
• Cannot separate solutions through filtering
15.2 Homogeneous Aqueous Systems >
6 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
15.2 Homogeneous Aqueous Systems >
7 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Solutions
• Methane, oils, grease, and gasoline, do not dissolve in water.
• However, oil and grease will dissolve in gasoline.
Solvents and Solutes
Nonpolar “like dissolves like”
15.2 Homogeneous Aqueous Systems >
8 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Solutions
Solvation: the process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called.
Solvated ions
Surface of ionic solid
The Solution Process
4/9/14
3
15.2 Homogeneous Aqueous Systems >
9 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
15.2 Homogeneous Aqueous Systems >
10 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
15.2 Homogeneous Aqueous Systems >
11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Electrolytes and Nonelectrolytes
Electrolytes and Nonelectrolytes
All ionic compounds are electrolytes • conducts an electric current when it
is in an aqueous solution or in the molten state.
• Dissociate into ions
15.2 Homogeneous Aqueous Systems >
12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Electrolytes and Nonelectrolytes
electric current must flow between the two electrodes
• Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water.
• Good conductors
To (+) electrode
To (–) electrode
4/9/14
4
15.2 Homogeneous Aqueous Systems >
13 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.
• Weak conductors
To (+) electrode
To (–) electrode
15.2 Homogeneous Aqueous Systems >
14 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Electrolytes and Nonelectrolytes
• Glucose, is a nonelectrolyte (does not dissociate in water).
To (+) electrode
To (–) electrode
15.2 Homogeneous Aqueous Systems >
15 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.
Ionization
NH3(g) + H2O(l) à NH4+(aq) + OH–(aq)
15.2 Homogeneous Aqueous Systems >
16 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.
• Perspiration
• Dehydration
4/9/14
5
15.2 Homogeneous Aqueous Systems >
17 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?
15.2 Homogeneous Aqueous Systems >
18 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.
15.2 Homogeneous Aqueous Systems >
19 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.
• Water in hydrates is weakly attached to the crystal, therefore easily removed.
Hydrates
• A substance that is anhydrous does not contain water.
15.2 Homogeneous Aqueous Systems >
20 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Hydrates
anhydrous CuSO4.
CuSO4�5H2O(s) CuSO4(s) + 5H2O(g) – heat
+ heat
Copper (II) sulfate pentahydrate
4/9/14
6
15.2 Homogeneous Aqueous Systems >
21 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 CoCl2).
• When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl2�6H2O).
15.2 Homogeneous Aqueous Systems >
22 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 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)
15.2 Homogeneous Aqueous Systems >
23 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Percent by mass H2O = x 100% mass of water mass of hydrate
Hydrates
To determine what percent by mass of a hydrate is water:
15.2 Homogeneous Aqueous Systems >
24 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate (Na2CO3�10H2O).
Sample Problem 15.1
Finding the Percent by Mass of Water in a Hydrate
4/9/14
7
15.2 Homogeneous Aqueous Systems >
25 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 H2O = x 100%
= 62.94%
180.0 g 286.0 g = x 100%
15.2 Homogeneous Aqueous Systems >
26 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).
15.2 Homogeneous Aqueous Systems >
27 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).
= 24.3 g + 32.1 g + (4 x 16.0 g) + 126.0 g
= 246.4 g
molar mass of MgSO4�7H2O
mass of H2O = 7 x ( 2 x 1.0 g + 16.0 g) = 126.0 g
126.0 g 246.4 g percent by mass H2O = x 100% = 51.14%
15.2 Homogeneous Aqueous Systems >
28 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Hydrates
Efflorescent Hydrates
• Vapor pressure hydrate > vapor pressure air
• effloresce.
H2O in hydrates - held by weak forces
so hydrates often have an appreciable vapor pressure.
4/9/14
8
15.2 Homogeneous Aqueous Systems >
29 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Hydrates
Hygroscopic Hydrates
• Compounds that remove moisture from air are called hygroscopic.
Vapor pressure hydrate < vapor pressure air
15.2 Homogeneous Aqueous Systems >
30 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Hydrates
Hygroscopic Hydrates
• Desiccant : compound used to absorb moisture from the air and create a dry atmosphere.
15.2 Homogeneous Aqueous Systems >
31 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Hydrates
Deliquescent Compounds
• Deliquescent: remove sufficient water from the air to dissolve completely and form solutions.
Beyond hygroscopic…