HC CH 15 sec 2 - Eastern Regional High Schoolweb.eccrsd.us/borda/public/honors/HC_CH15_2.pdf · strong electrolyte, is nearly 100% ... weak electrolyte, is only partially ... (II)

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15.2 Homogeneous Aqueous Systems >

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Chapter 15 Water and Aqueous Systems 15.1 Water and Its Properties 15.2 Homogeneous Aqueous Systems 15.3 Heterogeneous Aqueous Systems



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?



Solutions

Solutions What types of substances dissolve most readily in water?

•  An aqueous solution is water that contains dissolved substances.



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.

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Solutions

Solvents and Solutes •  Solutions are homogeneous mixtures.

•  Solute particles can be atoms, ions, or molecules.

•  Cannot separate solutions through filtering



Solutions

Substances that dissolve most readily in water include

ionic compounds

and

polar covalent compounds.




Solutions

•  Methane, oils, grease, and gasoline, do not dissolve in water.

•  However, oil and grease will dissolve in gasoline.


Nonpolar “like dissolves like”



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

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Which of these compounds should not dissolve in water?

A. HCl

B. C4H10

C. KI

D. NH3



Which of these compounds should not dissolve in water?

A. HCl

B. C4H10

C. KI

D. NH3



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




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

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•  Mercury(II) chloride, a weak electrolyte, is only partially dissociated in water.

•  Weak conductors

To (+) electrode

To (–) electrode




•  Glucose, is a nonelectrolyte (does not dissociate in water).

To (+) electrode

To (–) electrode




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)




Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells.

•  Perspiration

•  Dehydration

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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?



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.



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.



Hydrates

anhydrous CuSO4.

CuSO4�5H2O(s) CuSO4(s) + 5H2O(g) – heat

+ heat

Copper (II) sulfate pentahydrate

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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).



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)



Percent by mass H2O = x 100% mass of water mass of hydrate

Hydrates

To determine what percent by mass of a hydrate is water:



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

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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%



Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO4�7H2O).



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%



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.

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Hydrates

Hygroscopic Hydrates

•  Compounds that remove moisture from air are called hygroscopic.

Vapor pressure hydrate < vapor pressure air



Hydrates

Hygroscopic Hydrates

•  Desiccant : compound used to absorb moisture from the air and create a dry atmosphere.



Hydrates

Deliquescent Compounds

•  Deliquescent: remove sufficient water from the air to dissolve completely and form solutions.

Beyond hygroscopic…

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HC CH 15 sec 2 - Eastern Regional High Schoolweb.eccrsd.us/borda/public/honors/HC_CH15_2.pdf · strong electrolyte, is nearly 100% ... weak electrolyte, is only partially ... (II)