Investigating Solutions

Components of a Solution homogeneous mixture  at least 2 substances  proportions of the substances are not fixed (variable composition)  one phase 2 components a) Solvent - the substance that does the dissolving - present in the largest amount b) Solute - the substance that dissolves in the solvent (can be solid, liquid, gas) SOLUTION = SOLVENT + SOLUTE

Types of Solutions State of soluteSolventExamples Gas Air GasLiquidCarbonated drinks Liquid Alcohol in water 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

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

Factors continued 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

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

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 general 1.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

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 curve 2. SATURATED SOLUTION no more solute can be dissolved into the solution at a fixed temperature * any point ON the solubility curve 3. 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 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

Precipitation sudden appearance of a solid in a liquid Precipitate - solid that forms can be initiated by adding a single SEED CRYSTAL of the solute Seed Crystal - provides a nucleus where surplus solute can start crystallizing sometimes dirt, a sharp tap can initiate precipitation Test For Supersaturation - add a seed crystal to see if a precipitate appears