SOLUTIONS

Objectives

Describe the unique role of water in chemical and biological processes.

Distinguish between types of solutions such as electrolytes and nonelectrolytes and unsaturated, saturated, and supersaturated solutions.

Develop and use general rules regarding solubility through investigations with aqueous solutions.

Investigate factors that influence solubilities and rates of dissolution such as temperature, agitation, and surface area.

Calculate the concentration of solutions in units of molarity.

Use molarity to calculate the dilutions of solutions.

The Role of Water

Chemical Processes

Polarity

Hydrogen bonding

Surface tension

Capillary action

Specific heat

Three states of matter

Polarity

The oxygen atom is bigger than the hydrogen atoms, the electrons spend more time around the oxygen. This creates a slight charge on each end of the water molecule.

Hydrogen Bonding

The force of attraction between the hydrogen atom of one water molecule to the oxygen atom of another water molecule

Easily done because of water’s bent shape- allowing the hydrogen to bond.

Surface Tension

Attractive force between particles in a liquid that minimizes surface area

Water has a high surface tension due to hydrogen bonds.

Capillary Action

attractive force between the surface of a liquid and the surface of a solid

water mercury

Specific Heat

The amount of heat required to raise the temperature of one gram of a substance by one degree.

Water has a high specific heat meaning it takes a great deal of energy (heat) to raise the temperature

States of Matter

Naturally found in all three (solid, liquid, gas) on Earth

Water cycle

Density of solid form less than liquid

Biological Processes

Because less dense ice floats on liquid water, a beneficial environment is created – many living things stay alive during the winter when lakes and ponds freeze over.

The high specific heat of water also makes it conducive for aquatic life. A large body of water can absorb and store a large amount of heat from the Sun on a hot day with only a small effect on the temperature of the volume of water.

Biological Processes

When water freezes and expands, it has many different impacts. The most important is the weathering of rocks and minerals that produces the soil with minerals necessary for plant growth.

Evaporative cooling, such as from human sweat, is also important to life. Transpiration in plants functions as both a transport and a cooling mechanism.

Biological Processes

The chemical processes of life all happen in cells in water (aqueous solutions). Specifically, proteins function for support, transport, movement, protection, and coordination of organism activities. Carbohydrates necessary for fuel and energy storage are also in water solution.

The Nature of Solutions

Definitions

Solution - homogeneous mixture

Solvent - present in

greater amount

Solute - substance

being dissolved

Solvation

the process of dissolving

solute particles are separated and

pulled into solution

solute particles are surrounded by

solvent particles

Solvation

Dissociation separation of an ionic solid into aqueous ions

Ionization breaking apart of some polar molecules into aqueous

ions

Example

Example

Solvation

Detergents polar “head” with long nonpolar “tail” can dissolve nonpolar grease in polar water

NONPOLAR

NONPOLAR

POLAR

POLAR

“Like Dissolves Like”

Types of Solutions

SATURATED

SOLUTION

no more solute

dissolves

UNSATURATED

SOLUTION

more solute

dissolves

SUPERSATURATED

SOLUTION

becomes unstable,

crystals form

concentration

Concentration

The amount of solute in a solution.

Describing Concentration

% by mass - medicated creams

% by volume - rubbing alcohol

ppm, ppb - water contaminants

molarity - used by chemists

molality - used by chemists

Electrolytes

Strong

Electrolyte

Non-

Electrolyte

solute exists as

ions only

- +

salt

- +

sugar

solute exists as

molecules

only

- +

acetic acid

Weak

Electrolyte

solute exists as

ions and

molecules

Solutions Quiz

Fold your paper into thirds

On front flap-

Describe why water is the universal solvent.

On the inside flaps-

Describe and draw the three types of solutions: unsaturated, saturated and supersaturated

Solutions Quiz

Fold your paper into thirds

On front flap-

Explain polarity, hydrogen bonding and surface tension.

On the inside flaps-

Describe and draw the three types of solutions: unsaturated, saturated and supersaturated

Investigating solubility

Solubility

Solubility

maximum grams of solute that will dissolve in 100 g of solvent at a given temperature

varies with temperature

based on a saturated solution

Rate of Solution

Solids dissolve faster...

more stirring

small particle size (increased surface area)

high temperature

Rate of Solution

Gases dissolve faster...

no shaking or stirring

high pressure

low temperature

Solubility Curve

Solubility Rules

Molarity and dilutions

Molarity

Concentration of a solution.

solution of liters

solute of moles(M)Molarity

total combined volume

substance being dissolved

Preparing Solutions

To prepare a solution:

Know what Molarity you need

Know how much volume you need

Do the calculations, solve for grams

Place the number of grams you calculated into a beaker

Add the amount of volume you need of distilled water

Why distilled water?

Preparing Solutions

500 mL of 1.54M NaCl

• mass 45.0 g of NaCl • add water until total

volume is 500 mL

500 mL mark

500 mL volumetric flask

2211 VMVM

Dilution

Preparation of a desired solution by adding water to a concentrate.

Moles of solute remain the same.

Dilution

What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?

GIVEN:

M1 = 15.8M

V1 = ?

M2 = 6.0M

V2 = 250 mL

WORK:

M1 V1 = M2 V2

(15.8M) V1 = (6.0M)(250mL)

V1 = 95 mL of 15.8M HNO3

Preparing Solutions

250 mL of 6.0M HNO3 by dilution

measure 95 mL of 15.8M HNO3

95 mL of 15.8M HNO3

water for safety

250 mL mark

• combine with water until

total volume is 250 mL

• Safety: “Do as you

oughtta, add the acid to

the watta!”