Solutions

Solubility

Solubility Rules

Water

Most common solventA polar molecule

O -

a hydrogen bond

H +

H +

Hydrogen Bonds Attract Polar Water Molecules

Solute and Solvent

Solutions are homogeneous mixtures of two or more substances

Solute

The substance in the lesser amountSolvent

The substance in the greater amount

Nature of Solutes in Solutions

Spread evenly throughout the solution

Cannot be separated by filtration

Can be separated by evaporation

Not visible, solution appears transparent

May give a color to the solution

Types of Solutions

air O2 gas and N2 gas gas/gas

soda CO2 gas in water gas/liquid

seawater NaCl in water solid/liquid

brass copper and zinc solid/solid

(alloy)

Solute and Solvent

Identify the solute and the solvent.

A. brass: 20 g zinc + 50 g copper

solute = 1) zinc 2) copper

solvent = 1) zinc 2) copper

B. 100 g H2O + 5 g KCl

solute = 1) KCl 2) H2O

solvent = 1) KCl 2) H2O

Solution

A. brass: 20 g zinc + 50 g copper

solute = 1) zinc solvent = 2) copper

B. 100 g H2O + 5 g KCl

solute = 1) KCl

solvent = 2) H2O

Identifying Solutes

Identify the solute in each of the following solutions:

A. 2 g sugar (1) + 100 mL water (2)

B. 60.0 mL ethyl alcohol(1) and 30.0 mL

of methyl alcohol (2)

C. 55.0 mL water (1) and 1.50 g NaCl (2)

D. Air: 200 mL O2 (1) + 800 mL N2 (2)

Solution

Identify the solute in each of the following solutions:

A. 2 g sugar (1)

B. 30.0 mL of methyl alcohol (2)

C. 50 g NaCl (2)

D. 200 mL O2 (1)

“Like dissolves like”

A ____________ solvent such as water is

needed to dissolve polar solutes such as

sugar and ionic solutes such as NaCl.

A ___________solvent such as hexane

(C6H14) is needed to dissolve nonpolar

solutes such as oil or grease.

Saturated and Unsaturated

A saturated solution contains the maximum

amount of solute that can dissolve.

Undissolved solute remains.

An unsaturated solution does not contain all

the solute that could dissolve

Unsaturated or Saturated?

At 40C, the solubility of KBr is 80 g/100 g

H2O. Indicate if the following solutions are

(1) saturated or (2) unsaturated

A. ___60 g KBr in 100 g of water at 40C

B. ___200 g KBr in 200 g of water at 40C

C. ___25 KBr in 50 g of water at 40C

Solution

At 40C, the solubility of KBr is 80 g/100 g H2O.

Indicate if the following solutions are

(1) saturated or (2) unsaturated

A. 2 Less than 80 g/100 g H2O

B. 1 Same as 100 g KBr in 100 g of water

at 40C, which is greater than its solubility

C. 2 Same as 60 g KBr in 100 g of water,

which is less than its solubility

Is it soluble?

Which of the following solutes will dissolve in water? Why?

1) Na2SO4

2) gasoline

3) I2

4) HCl

Solution

Which of the following solutes will dissolve in water? Why?

1) Na2SO4 Yes, polar (ionic)

2) gasoline No, nonnpolar

3) I2 No, nonpolar

4) HCl Yes, Polar

Solubility

The maximum amount of solute that can dissolve in a specific amount of solvent usually 100 g.

g of solute

100 g water

Temperature and Solubility of Solids

Temperature Solubility (g/100 g H2O)

KCl(s) NaNO3(s)

0° 27.6 74

20°C 34.0 88

50°C 42.6 114

100°C 57.6 182

The solubility of most solids (decreases or increases ) with an increase in the temperature.

Temperature and Solubility of Solids

Temperature Solubility (g/100 g H2O)

KCl(s) NaNO3(s)

0° 27.6 74

20°C 34.0 88

50°C 42.6 114

100°C 57.6 182

The solubility of most solids increases with an increase in the temperature.

Temperature and Solubility of Gases

Temperature Solubility (g/100 g H2O)

CO2(g) O2(g)

0°C 0.34 0.0070

20°C 0.17 0.0043

50°C 0.076 0.0026

The solubility of gases (decreases or increases) with an increase in temperature.

Temperature and Solubility of Gases

Temperature Solubility (g/100 g H2O)

CO2(g) O2(g)

0°C 0.34 0.0070

20°C 0.17 0.0043

50°C 0.076 0.0026

The solubility of gases decreases with an increase in temperature.

Solubility of Gases

A. Why would a bottle of carbonated drink

possibly burst (explode) when it is left out

in the hot sun ?

B. Why would fish die in water that gets too warm?

Sol

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Summary

Properties of Solutions

1. homogeneous mixture if stirred during its formation

2. dissolved particles remain dissolved regardless of the time interval

3. a solution is clear and transparent 4. dissolved particles are extremely small

allowing for the solution to be filtered 5. considered to be a single phase

Types of Solutions 1. Gas/Gas 2. Liquid/Gas 3. Liquid/Liquid 4. Liquid/Solid 5. Solid/Solid

a. alloys b. amalgams

Terms to know: 1. solute - the substance being dissolved to form a

solution; usually in the lesser amount 2. solvent - the medium in which the solute is being

dissolved; usually in the greater amount 3. tincture - a solution in which the solvent is alcohol

(alcohol usually means ethanol or ethyl alcohol which has the formula, C2H5OH)

4. unsaturated - contains less solute that it is

capable of holding 5. saturated - contains the maximum amount of

solute that it is capable of holding 6. supersaturated - contains more solute that it is

capable of holding; metastable state which quickly returns to a saturated solution

7. solubility - the amount of a solute that can be

dissolved in a given amount of solvent 8. solubility curve - a plot which shows the amount

of solute that can be dissolved in a given amount of solvent and temperature

Factors affecting Solubility 1. Nature of the solute and solvent: the

expression, "Like dissolves like", describes this very well

2. Temperature - usually an increase in

temperature will increase the solubility of a solute in a given solvent. There are exceptions to this rule, but they are rare.

3. Pressure - affects only gaseous

solutions, those in which both the solute and solvent are gases and those in which one component is a gas and the other is a liquid

Factors Affecting the Rate of Solution 1. Size of the particles - in chemistry we

call this the surface area; the larger the surface area, the easier it is for a solute to dissolve

2. Stirring - more stirring increases the

contact between the solute and solvent and increases the rate of solution

3. Amount of solute already dissolved - as

the solute continues to dissolve, the solution will begin to approach the saturated state and the rate of dissolving will slow down

4. Temperature - for liquids and solids, an

increase will cause more solute to dissolve and to dissolve at a faster rate; the opposite is true for gas solutions