Chapter 15

Solutions

Solution types & parts Solutions can be:

Solids – brass, dental fillings, chocolate barLiquids – sodas, vinegar, salt waterGaseous – air

Parts of a solution: Solute – the substance being dissolved.

Solvent – the substance that dissolves the solute. The most common, most abundant solvent is water. Water is known as the universal solvent.

15-1 How Solutions Form

DissolvingWhere does dissolving occur? At the surface of a solid. The process continues until all particles of the solid have made contact with water to form solutions. For two solids, they must both be melted & mixed together.

Rate of dissolving – to dissolve faster:Crush – to expose more surface areaShake / StirIncrease the heatAdd more water / solvent

To dissolve gas in liquid faster: cool the liquid & increase the pressure of the gas.

15-1 How Solutions Form

97% of Earth’s water is in the oceans. The oceans contain sodium chloride, magnesium salts, and calcium salts. Because our need for freshwater is increasing, we need to be able to desalinate (take out the salt) the ocean water.

Distillation can remove the salts to make fresh water: Salt water is boiled, the water vapors go through tubing where they are collected and condensed, then collected as fresh water. The salts will not evaporate. (p. 386, p.387)

15-2 Oceans – the World’s Largest Solution

Solubility – is the maximum number of grams of solute that can dissolve in 100.0 g of solvent at a certain temperature.

Sugar’s solubility: 203.9g / 100. g water at 20°C Concentration –

A concentrated solution has a large amount of solute dissolved in the solvent; a dilute solution has a small amount of solute in the solvent; BOTH are RELATIVE TERMS used for comparison. Calculating concentration – concentration is usually expressed as a percentage: 25 mL juice (solute) per 100 mL solution = 25%

15 – 3 Solubility & Concentration

Limits of solubility Saturated solution can hold no more solute (nothing else will dissolve)

How can you make more solute dissolve?Heat the solution then add more solute

Unsaturated solution – can hold more solute; (more solute will dissolve) Supersaturated solution has MORE solute than normal at that temperature.

Heat the solution, dissolve the max amount of solute, then cool the solution.

15 – 3 Solubility & Concentration

Calculating concentration – concentration is usually expressed as a percentage: 42.58 mL juice (solute) per 100 mL solution = 42.58%

page 390 example

88 g KCl = ? g KCL 100 mL solution 50 mL

88gKCl (50 mL) / 100 mL = 44 g KCl

Solve the Practice Problems

15 – 3 Solubility & Concentration

15 – 4 Particles of SolutesSolvents & Solutes•Polar solvents dissolve polar solutes (water is polar so it will dissolve sugar, salt and other polar solutes). “like dissolves like” means substances will dissolve substances chemically like itself.•Non-polar substances dissolve only non-polar solutes (oil is non-polar so it doesn’t dissolve in water).•Some substances (ethanol) have a polar and non-polar end on its molecule so it can dissolve in polar and non-polar solvents.

15 – 4 Particles of Solutes•Solutions as Conductors

•When an ionic solid dissolves in water, the positive and negative ions are dissociated (separated). •When electrolytes ionize in water, they will conduct electricity.

•When nonelectrolytes such as sugar and alcohol can dissolve in water, but they do not conduct electricity.

15 – 4 Particles of Solutes• Effects of solute particles

• Adding a solute to a solvent lowers the freezing point of the solvent. •As a solvent freezes, the particles become organized into an orderly pattern. Solute particles interfere with this pattern, preventing the solvent from freezing at the normal temp. (Ex: Antifreeze in a car, salt on ice in an ice cream freezer.)• Solutes can also raise the boiling point of water because the attraction between solute and solvent particles interferes with evaporation so the solution boils at a higher temp.