Solutions and Solubility

Solution - What is it?

A solution is a mixture of two or more kinds of molecules, atoms, or ions (or chemical compounds) that is homogeneous or appears to be all one thing.

What are solutions made of?

Solution

Solute Solvent

The substance being dissolved

The substance doing the dissolving

Solvent

SoluteSolution

Identify the Solute/Solvent

1. Instant coffee dissolved in hot water. Sugar is also added to the solution.

2. Antifreeze consists of methanol dissolved in water. Blue colouring is also added as a safety precaution.

3. Carbonated drinks (soft drinks) consist of a flavoured liquid containing dissolved carbon dioxide gas.

4. Water, oil and salt are mixed together.

• Pure substances, such as pure water, have a fixed composition. You cannot change the ratio of hydrogen to oxygen in water.

• Solutions, on the other hand, have variable composition, which means that different ratios of solvent to solute are possible.

Weak tea

Strong tea

• When a solvent dissolves a solute, no chemical reaction occurs. The solvent and the solute can be separated using physical measures, such as boiling or melting.

• A solution can be a gas, a liquid, or a solid. Various combinations of solute/solvent states are possible. Air is a mixture of nitrogen, oxygen, argon, and carbon dioxide gases. A gas can be dissolved in a liquid and a solid can be dissolved in another solid.

Solute Solvent Example

Gas Gas Air (oxygen in nitrogen)

*Gas Liquid Soft drink (carbon dioxide in water)

Gas Solid Ice (oxygen in ice)

Liquid Gas Humid air (water in air)

*Liquid Liquid Antifreeze (methanol in water)

Liquid Solid Tooth fillings (mercury in silver)

*Solid Liquid Syrup (sugar in water)

Solid Solid Alloys (bronze is tin in copper)

Classification of Solutions* are most common to chemistry

Some special terms for solids dissolved in liquids

• Insoluble- a solid

that does not

dissolve in a given

liquid

Soluble- a solid

that dissolves in a given liquid

Some special terms for liquids dissolved in liquids

• Immiscible- two liquids that do not dissolve in each other

• Have you heard the old expression "Oil and water do not mix?"

• This is an example of two immiscible liquids.

Some special terms for liquids dissolved in liquids

• Miscible liquids are those that can mix with each other.

• Have you ever made chocolate milk by mixing milk and liquid chocolate syrup?

• The two liquids mixed well and became a single solution -- and a tasty one, too! That's because they were miscible with each other, or mixed well.

Aqueous solutions (aq)

• Water is known as the universal solvent

• The polar nature of the water molecule enables it to dissolve many ionic and covalent compounds.

IMPORTANCE OF WATER AS A SOLVENT

 • Drinking water is a solution containing many dissolved

substances. These substances may affect the taste, appearance and toxicity of the water.– Purification of drinking water is of vital importance.

 • Blood contains many essential substances dissolved in

water, such as glucose, hormones, oxygen, minerals and waste.

• Oxygen must first be dissolved in water before it can diffuse into an organism's gas exchange system.

• Many chemical reactions occur faster if substances are dissolved in water first.– This increases surface contact between the reactants.

Water’s Dark side…

The polarity of a water molecule allows it to attack ionic compounds and rip their bonds apartThis is how they dissolve!

The water molecules surround the ions on the surface of the crystal.

The slightly positive hydrogen atoms are attracted by the negative chloride ions, and the slightly negative oxygen atoms are attracted by the positive sodium ions.

Vitamins

• Multi Vitamin– Provides many

essential vitamins– “Expensive urine”

• Water Soluble– Vitamin C– Must be replenished regularly

• Fat Soluble– Can overdose – Vitamin A– Can be ingested periodically,

stored in body fat

*** Not all ionic compounds are soluble in water. The strength of the ionic bonds within the lattice determine

its solubility in water.***

Compounds with strong ionic bonds are hard to pull apart. The water molecules will only be weakly attracted.

The compound is insoluble.Compounds with weak ionic bonds are easy

to pull apart. The water molecules are strongly attracted. The

compound is very soluble.When ions are surrounded by water

molecules they become hydrated.

So… why do they dissolve?

Remember, there are 3 forces of attraction in play:

1. Attraction between 2 SOLUTE particles

2. Attraction between 2 SOLVENT particles

3. Attraction between a SOLUTE and SOLVENT particle

If the force of attraction between 2 DIFFERENT particles in a mixture are stronger than those between LIKE particles, a solution forms.

Solubility

The mass of a substance that will dissolve in a given volume of solvent at a specific temperature is referred to as solubility.

If there is a large % of solute, it is said to be concentrated

If there is a low % of solute it is dilute (fewer solute particles per volume of solvent)

Dissolution is the rate at which a substance dissolves

Types of Solutions

• Unsaturated- still able to dissolve more solute

• The crystals of solute added will continue to disappear.

• Saturated- maximum amount of solute that will dissolve

• Nothing will occur with the addition of more solute

• Supersaturated- past saturation…(by heating) crystals may and usually come out of solution.

• The addition of more solute causes the precipitation of the solute to the saturation point.