Mixtures Chapters 2 and 15

Types of Matter  Matter – anything that takes up space and has mass –“see” atoms with STM –Element – a substance that contains only 1 type of atom –Compound – a substance made of atoms combined by bonding in whole number ratios  Phases of matter: –Solid – least energy, definite shape and volume –Liquid – mid energy, definite volume but not shape –Gas – most energy, no fixed shape or volume –All types of matter can become all phases if they get hot or cold enough

Changes in Matter  Physical change –The molecules/elements involved aren’t changed (no new substance is formed) –Often reversible –Ex. Phase change, mixtures  Chemical change –A reaction occurs and new compounds are formed (new substances are created) –Often permanent –Ex. Rusting, cooking, burning, rotting

Mixture  A physical combination of 2 or more substances –Can be elements or compounds –Nothing new is formed (physical change) –Can be separated back into its components by filtering, distillation, chromotography, or other physical means –Can be between things of the same phase or things in various phases –Ex. Salt water, atmosphere, gold jewelry

Types of Mixtures  Homogeneous –Resulting mixture is the same throughout (evenly mixed) –Also called a solution –Ex. Salt water  Heterogeneous –Resulting mixture has different concentrations of the parts in different places –Ex. Sand and water, chocolate chip cookies

Parts of a Solution  Solvent – the thing that is present in the larger amount in a solution –Water is the universal solvent (many things dissolve in it)  Solute – the thing that is present in the lesser amount in a solution  The solute is dissolved into the solvent to make a solution  Both the solute and solvent can be in any phase  Polar solvents dissolve polar solutes, nonpolar solvents dissolve nonpolar solutes

How Solutes Dissolve  In order for a substance to dissolve in a solvent, a “hole” must be created for that molecule to fit into –They must have the same types of intermolecular interactions as the solvent –The solute replaces the interactions that occur normally between molecules of the solvent –Remember, ionic compounds split into 2 separate ions when placed in water. These ions then interact with the polar water molecules, which is why they dissolve in water.

Increasing Dissolution  Heat the solution –It increases the molecular speed and so increases the interactions between solute and solvent  Increase the surface area of the solute –More parts of the solute touching the solvent increases the interactions  Stir the solution –Like temperature, movement increases the interactions

Adding Solutes Changes the Physical Properties of a Substance  Colligative property – the amount of a substance matters more than the type of substance involved –More particles gives a greater effect  Adding solute increases the boiling point of a substance –Interactions with solute keep water from being able to escape in air bubbles  Adding solute decreases the freezing point of a substance –Interactions with solute keep water from being able to create the intermolecular forces required to create a solid

Concentrations of Solutions  Concentrated – a lot of solute is dissolved  Diluted – a little solute is dissolved  Unsaturated – more solute could still be dissolved  Saturated – any more solute would be unable to dissolve  Supersaturated – the solution has been “tricked” into dissolving more solute than normally possible

Mass Percent  Way to measure the concentration of a solution  Mass % = mass solute x 100 mass solution mass solution  Ex. What is the mass percent of a salt water solution if 1.0 g of NaCl is dissolved into 49.0 g of water? 1 g x 100 = 2.0% 50g

Molarity  Another way to measure concentration –Better than mass % because the mass of the compounds don’t matter  M = mol solute liters solution liters solution  Ex. What is the molarity of a 1.50 L solution containing 11.5 g NaCl? 11.5 g NaCl1 mol NaCl=0.288 mol 40 g NaCl M = mol=0.192 M NaCl 1.50 L

Diluting Solutions  Solutions are often stored in the lab at high concentrations to conserve space, then diluted by adding more solvent to create a usable concentration  M 1 V 1 = M 2 V 2  Ex. What volume of 16 M HCl must be used to prepare 1.5L of a 0.1 M HCl solution? 16 (V) = 0.10 (1.5) V = L