Solvent, Solute, Solutions and Solubility

Solutions• All solutions consist of 2 parts– Solvent (the substance that does the dissolving,

makes up the majority of the solution – usually liquid, but can also be solid or gas)

– Solute (the substance that dissolves – can be solid, liquid or gas)

Solution

Solvent

Solute

A solution is formed when a solute dissolves in a solvent

State at RTP

Solid Liquid Gas

Solvent Iron Water Nitrogen

Solute Chromium Sugar Oxygen, carbon dioxide and other gases

Solution Stainless steel(Metal alloy)

Sugar syrup Air

Liquid solutions at rtp – Solvent = Water?

• Usually, we use water as a solvent because many substances can dissolve readily in it.

• However, the solvent does not have to be water!

• Substances that do not dissolve in water may be soluble in other solvents

• E.g. ethanol (an alcohol), oil..

We shall focus mainly on aqueous solutions

• Chlorine– Greenish-yellow gas– Low melting and

boiling point– Poor electrical

conductor

Chlorine is used in bleaches for our clothes.

Solvent :

Solute :

Water

Chlorine gas

7Uses: antiseptic

Iodine is a non-metallic element that sublimes when heated to form a violet vapour.

When dissolved in ethanol, it forms tincture of iodine, used as an antiseptic.

Solvent :

Solute :

Ethanol

Iodine

Is a solution a..

• Element?• Compound?• Mixture?

Mixture!No fixed proportion of

solute / solvent required

Solubility• The solubility of a substance in a

solvent is the maximum quantity of that substance which can dissolve in 100 g of the solvent at a given temperature

• (units: g / 100 g)

• Copper(II) sulfate has a solubility of 32 g /100 g in water (at 20°C)

Describing solutions

• Copper(II) sulfate has a solubility of 32 g /100 g of solvent (at 20°C)

• 100 g of water (100 ml)– 2 g of copper(II) sulfate

– 30 g of copper(II) sulfate

– 32 g of copper(II) sulfate

– 35 g of copper(II) sulfate

Dilute solution

Concentrated solution

Saturated solution

Suspension

Factors affecting solubility?• Type of solute – e.g. copper(II) sulfate / salt

/ sugar• Type of solvent– e.g. water / ethanol

• Temperature of solvent– Generally, solubility as

temperature • Pressure of surroundings– Generally, solubility as

pressure

Suspension?

The amount of substance present is over its solubility limit

35 g 100 g

Copper(II) sulfate has a solubility of 32 g /100 g of solvent (at 20°C)

Suspension?

The substance does not dissolve in the solvent

Solutions Suspensions

What happens when it is passed through filter paper?

No visible changeSolid particles are trapped on filter paper

What happens when it is left to settle?

No visible changeSolid particles settle on the bottom of the beaker

Is it homogenous (same throughout)? Yes No

Can light pass through?

Yes – solutions are ALWAYS CLEAR!

No – a suspension is ALWAYS CLOUDY.

Common errors..

• Clear solution?• Transparent solution?• Colourless solution!

• Cloudy solution?• White colour solution?• Milky solution?• Suspension! (White precipitate in a colourless solution)

X

XX X

X

Rate of dissolving

Rate of dissolving is NOT solubility!

• Recall:

• Rate of dissolving: How fast it dissolves

• The solubility of a substance in a solvent is the maximum quantity of that substance which can dissolve in 100 g of the solvent at a given temperature

Making solutions quickly

• Factors affecting rate of dissolving– Temperature of solvent– Particle size of solute– Stirring

• Assumption: The amount of solute used is << solubility limit