Solutions

Properties of Water

Solutions

Predict the % water in the following foods

Predict the % water in the following foods

88%

water

94% water

85%

water

86% water

Water in the Body

water gain water loss

liquids1000 mL urine 1500 mL

food 1200 mL perspiring 300 mL

cells 300 mL exhaling 600 mL

feces 100 mL

Calculate the total water gain and water loss

Total ______ mL _____ mL

Water

Most common solventA polar molecule

O -

a hydrogen bond

H +

H +

Hydrogen Bonds Attract Polar Water Molecules

Explore:Surface Tension

Fill a glass to the brim with water

How many pennies can you add to the glass without causing any water to run over?

Predict _________________

Actual _________________Explain your results

Explore

1. Place some water on a waxy surface. Why do drops form?

2. Carefully place a needle on the surface of water. Why does it float? What happens if you push it through the water surface?

3. Sprinkle pepper on water. What does it do? Add a drop of soap. What happens?

Surface Tension

Water molecules within water hydrogen bond in all directions

Water molecules at surface cannot hydrogen bond above the surface, pulled inward

Water surface behaves like a thin, elastic membrane or “skin”

Surfactants (detergents) undo hydrogen bonding

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

gaseosa CO2 gas in water gas/liquid

seawater NaCl in water solid/liquid

brass copper and zinc solid/solid

Discussion

Give examples of some solutions and explain why they are solutions.

Test yourself

(1) element (2) compound (3) solution

A. water 1 2 3

B. sugar 1 2 3

C. salt water 1 2 3

D. air 1 2 3

E. tea 1 2 3

Answers

(1) element (2) compound (3) solution

A. water 2

B. sugar 2

C. salt water 3

D. air 3

E. tea 3

Test yourself

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

Answers

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

Test yourself

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)

Answer

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 non-polar

solutes such as oil or grease.

Self test

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

1) Na2SO4

2) gasoline

3) I2

4) HCl

Answer

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

1) Na2SO4 Yes, polar (ionic)

2) gasoline No, non-polar

3) I2 No, nonpolar

4) HCl Yes, Polar

Formation of a Solution

Cl-

Na+ Cl-Na+

H2O

H2O

Na+

Cl-

solute

Dissolvedsolute

Hydration

Writing An Equation for a Solution

When NaCl(s) dissolves in water, the reaction can be written as

H2O

NaCl(s) Na+ (aq) + Cl- (aq)

solid separation of ions in water

Self test

Solid LiCl is added to some water. It dissolves because

A. The Li+ ions are attracted to the

1) oxygen atom(-) of water

2) hydrogen atom(+) of water

B. The Cl- ions are attracted to the

1) oxygen atom(-) of water

2) hydrogen atom(+) of water

Answer

Solid LiCl is added to some water. It dissolves because

A. The Li+ ions are attracted to the

1) oxygen atom(-) of water

B. The Cl- ions are attracted to the

2) hydrogen atom(+) of water

Rate of Solution

You are making a chicken stock using an oxo cube. What are some things you can do to make it dissolve faster?

Crush it

Use hot water (increase temperature)

Stir it

Self test

You need to dissolve some gelatin in water. Indicate the effect of each of the following on the rate at which the gelatin dissolves as (1) increase, (2) decrease,

(3) no change

A. ___Heating the water

B. ___Using large pieces of gelatin

C. ___Stirring the solution

Answer

You need to dissolve some gelatin in water. Indicate the effect of each of the following on the rate at which the gelatin dissolves as (1) increase, (2) decrease,

(3) no change

A. 1 Heating the water

B. 2 Using large pieces of gelatin

C. 2 Stirring the solution