Solutions and Solubility

Solubility

• What does it mean to dissolve?

Compounds

Compounds are two or more elements chemically joined (held together by chemical bonds)

There is a fixed ratio of components

Properties of compound are different from those of the components

Compounds can be separated only by chemical means

MixturesMixtures are two or more substances (elements

or compounds or both) that do not combine chemically during the mixing.

There is a variable proportion of

components

Properties of each component remain the same as before mixing

Parts can be separated by physical means

More Mixture types

Alloy: mixture of 2 or more metals melted together having new and different properties, examples: bronze, brass, pewter

Steel is an alloy of iron and carbon.Amalgam: mixture containing mercury

Solvent – the substance that is doing the dissolving. It is present in the greatest amount.

Solute – the substance that is being dissolved

Solution – the solute and the solvent together. It is a homogeneous mixture of two or more substances.

Which of these is

the solvent?

Solubility

• When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

Solubility

• Chalk and talc do not have solubility values.

• These substances are insoluble in water because they do not dissolve in water.

Solubility

• A solution is saturated if it contains as much solute as the solvent can dissolve.

• Any solute added in excess of the substance’s solubility will not dissolve.

• A supersaturated solution means there is more dissolved solute than the maximum solubility.

• Concentration - a measure of the exact amount of solute dissolved in a given amount of solvent.

Concentration units - similar to density units g of solute 100 mL of solvent

or simply g/100mL

Concentrations may be expressed as:

unsaturated – able to hold more solute

saturated – holding exactly the max solute possible

To calculate concentration EXACTLY use this formula:

C = mass of solute volume of solvent x 100

SolubilitySolubility is a measure of how much

substance (solute) will dissolve at a certain temperature, in a certain amount of water or other liquid (solvent)

For Example…

12g of sugar will dissolve in 100mL of water at room temperature. If you heat the water up to 80°C, then 30g of sugar will dissolve. If you increase the volume of water to 200mL, then twice as much sugar will dissolve as before.

When expressing the solubility of something you must give the amount of water used as well as the temperature.

Solubility is a Characteristic Property

Solubility changes with temperature so the best way to show the solubility of a substance is on a graph

Solubility RulesSolid solutes:

Dissolve faster AND more in hotter solvents

Dissolve faster if stirred or crushed up

Solubility Rules

Like Dissolves LikePolar molecules dissolve polar molecules –

(a polar molecule has a negative pole on one side and a positive one on the other). The charged particles attract one another and molecular motion spreads the solute evenly through the solvent

Solubility Rules

Non –polar molecules dissolve non-polar molecules without charges being involved. A different kind of attractive force works on non-polar molecules.

Solubility Rules

Gaseous solutes:

• Dissolve faster AND more in colder solvents

• Come out of solution when stirred or shaken

• Like Dissolves Like

Solubility of Gases in Liquids

• When you drink carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

• The solubility of gases in liquids increases with pressure.

Liquid Solutes

• Oil and vinegar salad dressing separates because oil is not soluble in water.

• Liquids that are not soluble in water may be soluble in other solvents.

Water as a solvent

• Water is often called the “universal solvent.”

• Water is a good solvent because of the way the H2O molecule is shaped.

Water as a solvent

• A water molecule has a negative end (pole) and a positive end.

• A molecule (like water) with a charge separation is called a polar molecule.

Water as a solvent

• Water dissolves sodium chloride (salt) to form a solution of sodium (+) and chlorine (-) ions.

Water as a solvent

• In general, like dissolves like: –water dissolves polar

substances–non-polar solvents

dissolve non-polar substances

Solutionssolution - a liquid homogeneous mixture containing a

dissolved substance

solvent - substance that dissolves the solute. The component in largest concentration.

solute - substance being dissolved. The component in smallest concentration

aqueous - solvent is water

tincture - solvent is alcohol

More on Solutions

Dilute solutions: small amount of solute compared to amount of solvent

Concentrated solution: contains more solute than a dilute solution

Saturated solution: when solvent cannot hold any more solute at a given temperature