Solutions

Solutions Goals a. Describe solutions in terms of • solute/solvent • conductivity • concentration b. Explain factors affecting the rate a solute dissolves in a specific solvent. c. Explain that solubility is related to temperature by constructing and reading a solubility curve.

A solution is made up of two parts—a solute and a solvent. A solute is the substance being dissolved, while a solvent is the substance doing the dissolving. For example, in a saltwater solution, salt is the solute and water is the solvent. The ability of a substance to dissolve in another substance is called solubility. Clip

Ex: Antifreeze (ethylene glycol). Effects of Adding a Solute to a Solvent Freezing point depression Raising of the boiling point Adding a solute interferes with the formation of the solid making it harder for the solvent to freeze. Ex: Antifreeze (ethylene glycol). Solute particles interfere with the evaporation process and more energy is needed for the molecules to escape into the gas phase.

Solutions and Conductivity Solutions can only conduct electricity if the atoms ionize (break apart into ions) Solutions that conduct electricity are called electrolytes. Solutions that do not conduct electricity are called nonelectrolytes. They do not produce ions in solution. Strong vs. Weak Electrolytes Strong: Ionize completely. NaCl Weak: Produce few ions in solution.

For Gases: Pressure above the solvent Factors affecting the rate a solute dissolves in a specific solvent. What Affects the rate at which a solute will dissolve in a solvent? Increased surface area increases the rate of dissolving. Remember: dissolving occurs at the surface. Crystal Size Temperature For Gases: Pressure above the solvent Increases the speed of the molecules in the solvent. More atmospheric pressure pushing down on the solvent makes it harder for the gas molecules to escape the solvent. Dissolving Website

Factors affecting the rate a solute dissolves in a specific solvent. Polar Molecular Structure Nonpolar Polar solutes dissolve in Polar solvents Nonpolar solutes dissolve in Nonpolar solvents EX: Water and HCl EX: Gas and Oil “Like dissolves like” Clip

Concentration Concentrated Dilute NOT VERY Precise! A lot of solute in a little solvent A little solute in a lot of solvent NOT VERY Precise! To be more precise we need to express the concentration by volume. Usually as a percentage by volume. In order to compare concentrations, we express the amount dissolved in 100g of water.

Solubility Curves As the temperature increases... The amount of oxygen that is able to dissolve in water… decreases.

Can dissolve more solute at a given temperature Unsaturated Saturated Supersaturated Can dissolve more solute at a given temperature Contains all of the solute it can hold/ dissolve at a certain temperature Contains more solute that a saturated solution at a given temperature. Can be created by cooling a saturated solution without disturbing it- no solute come out of solution. Clip

Solubility Curves 50g of NaCl @ 20˚C? 56g of NaCl @ 20˚C? 30g of KNO3 @ 120˚C? 50g of NaCl @ 20˚C? 56g of NaCl @ 20˚C? 120g of KNO3 @ 20˚C? How would you make a saturated sol. of KNO3 at 80˚C? 110 80 70 60 50 40 30 20 10 20 40 60 80 120 180