Solutions CH 13

Two Types of Mixtures Homogeneous Same throughout, looks pure EX: Air Heterogeneous Different throughout EX: Sand

A solution is any substance — solid, liquid, or gas — that is evenly distributed throughout another substance. Solutions are homogeneous mixtures EX: Brass which is a mixture of copper and zinc

A Solution contains … Solvent — the dissolving medium Higher concentration EX: alcohol and water Water is the universal solvent! Solute — being dissolved Lower concentration

Example You are making Kool- Aid. What is the solute and what is the solvent?

The same substance can be a solute in one instance and a solvent in another. EX: 15% alcohol solution: Water is the solvent and alcohol is the solute EX: 85% alcohol solution: Alcohol is the solvent and water is the solute

Types of Solutions

Suspension A mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas. EX: mud — will settle out over time Large particles

Colloid A mixture consisting of tiny particles that are intermediate in size between those in solution that are suspended in a liquid, solid, or gas. EX: milk — particles do not settle out over time.

Alloys Two or more solid metals mixed together EX: Steel, brass

Separating Mixtures

Decanting Pouring off the liquid from a settled suspension EX: mud

Centrifuge Separates substances by their densities EX: milk — separates fat out blood

Filtration Liquid goes through a filter and the solid is left behind EX: ground coffee

Evaporation Liquid turns into a gas and the solid is left behind EX: salt water

Chromatography Separates different dyes by choosing the correct solvent

Distillation Separating liquids by boiling points

Electrolytes Solutions that conduct electricity Compounds EX: NaCl

Solvation The process of dissolving a solute in a solvent Hydration — ions that are surrounded by water molecules Dissociation — the decomposition of a crystal into hydrated ions EX: NaCl  Na + (aq) + Cl - (aq)

Polar molecules solvate! Attractions between polar molecules may draw the solution components into a smaller volume EX: 50 mL ethanol + 50 mL of water = <100mL

Miscible — no apparent limit to the solubility of one substance in another Immiscible — two liquids that don ’ t mix Like dissolves like!

Solubility — the amount of substance needed to make a saturated solution at a given temperature. EX: We use glass in lab because of its low solubility.

Factors that affect solubility

Liquids: T increases, solubility increases EX: rock candy Supersaturated solution — add heat to make dissolve Gases: T increases, solubility decreases EX: Coke and CO 2

P increases, solubility increases Surface area increases, rate of dissolving increases Agitating increases, rate of dissolving increases T increases, rate of dissolving increases

Henry ’ s Law States that at constant T, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas on the surface of the liquid. EX: Coke can S 1 = S 2 P 1 P 2

Saturated solution — contains the maximum amount of solute for a given amount of solvent at a constant T Supersaturated solution — a solution contains more solute than it should theoretically at a given T

Concentrations

Concentration — how much of a substance a solution contains ppm — parts per million Dilute solutions — contains low concentration of solute Concentrated solutions — contains high concentrations of solute

Molarity Molarity — the number of moles solute dissolved in each liter of solution. (M) M = mol / L **You have 500 mL of a 4M HCl sol ’ n. You take out 100 mL, you still have a 4M sol ’ n.

Example 1 How many moles of HCl are contained in 1.45 L of a 2.25M solution?

Solution 1 M = mol / L mol = M x L mol = 2.25 M x 1.45 L mol = 3.26 mol HCl

Example 2 Give the directions for the preparation of 2.50 L of a 1.34 M NaCl solution. (HINT: You need to find the number of g NaCl needed)

Solution 2 Step 1: Calculate the number of moles: mol=1.34 M x 2.5 L = 3.35 mol NaCl Step 2: Convert moles to grams 3.35 mol NaCl x 58.5 g NaCl = 196 g 1 mol NaCl

Dilutions Make solutions less concentrated by diluting it with a solvent Since only the solvent changes, the number of moles stays the same Moles solute before dilution = moles solute after dilution Moles of solute = M x V (liters of solution) So … M 1 V 1 = M 2 V 2