Investigating Solutions

Components of a Solution

Homogeneous mixture at least 2 substances proportions of the substances are not fixed

(variable composition) one phase

2 componentsa) Solvent - the substance that does the dissolving

- present in the largest amountb) Solute - the substance that dissolves in the solvent (can be solid, liquid, gas)

SOLUTION = SOLVENT + SOLUTE

Types of SolutionsState of solute Solvent Examples

Gas Gas Air

Gas Liquid Carbonated drinks

Liquid Liquid Alcohol in water

Solid Liquid Salt Water

Solid Solid Alloys (copper-nickel alloy)

Concentrated solution vs Dilute solution

Concentrated• Higher

percentage of solute

• Dissolved ions are close together

Dilute• Low percentage

of solute• Ions are farther

apart

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Solubility• maximum amount of that substance

which will dissolve in a fixed quantity of the solvent at a specified temperature

• Example: mass of solute that dissolves in 1 kg of solvent at a given temp.

Factors That Affect Rate of dissolving

1. For most solids, the rate of dissolving is greater at higher temperatures.

2. Agitating a mixture by stirring or by shaking the container increases the rate of dissolving

3. Decreasing the size of particles increases the rate of dissolving

More Factors

Solubility and attraction - When forces of attraction between different particles are stronger than the forces of attraction between like particles in the mixture, a solution forms.

Polar and Non-polar substances

1. Polar substances dissolve in polar solvents (sugar in water)

2. Non-polar compounds dissolve in non-polar solvents (iodine in benzene)

Solubility and Intermolecular Forces

Dipole-Dipole Attractions

• Attraction between charges on two different polar molecules

• Weak forces of attraction

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Ion-dipole attractions• Attractive forces between

an ion and a polar molecule• Negative ends of water

attract cation (+ve)• Positive end of water

attracts the anion (-ve) Generally an ionic

compound will dissolve in a polar solvent

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Solubility of Covalent Compounds

• Covalent compounds do not have negative and positive charges to attract water molecules

• Generally they are not soluble in water

Predicting solubility

In general1. Ionic solutes and polar covalent

solutes both dissolve in polar solvents.

2. Non-polar solutes dissolve in non-polar solvents.

Factors that Affect Solubility

1. Small molecules are often more soluble that larger molecules

2. Temperature and solubility– Solubility of most solids increases

with temperature– Solubility of most liquids is not

greatly affected by temperature– Solubility of gases decreases with

higher temperature

3. Pressure and solubility– changes in pressure have hardly

any effect on solid and liquid solutions

– Solubility of the gas is directly proportional to the pressure of the gas above the liquid

Solubility Curves

• solubility of a solute changes with temperature

• solubility of each compound is different at different temperatures

• solubility of each compound changes in a different way as temperature changes

UNSATURATED, SATURATED AND SUPERSATURATED SOLUTIONS

1. UNSATURATED SOLUTION• more solute can be dissolved while the temperature remains

constant• *any point in the region under the solute’s solubility curve2. SATURATED SOLUTION• no more solute can be dissolved into the solution at a fixed • temperature• * any point ON the solubility curve3. SUPERSATURATED SOLUTION• solution containing more dissolved solute than normal at a

particular temperature• unstable• may suddenly form solid crystals leaving only a saturated

solution behind• * any point ABOVE the solubility curve

Solubility curve for KClO3

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90Temperature (*C)

10 g

/ 10

0 g

Calculations using solubility curvesCalculations using solubility curvesUsing The Graph On the Previous Slide1. Is the solution saturated, unsaturated or supersaturated if there are

20g of KClO3 at 30°C

2. Is the solution saturated, unsaturated or supersaturated if there are 5g of KClO3 at 50°C

3. Is the solution saturated, unsaturated or supersaturated if there are 20g of KClO3 at 50°C

4. 100 g H2O is saturated with KClO3 at 100°C. How much KClO3

will come out of solution if the temperature is decreased to 48°C?

57 g-18 g = 39 g

Saturated

Unsaturated

Supersaturated