Solutions

Solutions Definition: Homogeneous mixture of two or more substances in a single phase. Like Dissolves Like (i.e. nonpolar molecules dissolve in nonpolar molecules) Solid mixtures: alloys (brass, sterling silver) Liquid mixtures: alcohol & water Gas mixtures: air

Other Terms Soluble: capable of dissolving Insoluble: incapable of dissolving Miscible: 2 liquids dissolve into each other Immiscible: 2 liquids do not dissolve into each other Solubility: how much of a given solute a certain solvent can dissolve at a certain temperature & pressure

Components of Solutions Solute: is dissolved by the solvent. Found in lesser quantities May be electrolytes (conduct electricity) or non- electrolytes (does not conduct electricity) Solvent: does the dissolving Water is the universal solvent ich ich

Rates of Dissolving Rate of dissolving may speed up due to the following: 1. Increased Surface Area: breaking the solute up into smaller pieces 2. Increased Stirring: increases particle collisions 3. Heating: particles move faster = more collisions.

Solubility Varies with temperature Solids & Liquids: Temp ↑, solubility ↑ Gases: Temp ↑, solubility ↓ Henry’s Law: Solubility of a gas in liquid is directly proportional to pressure

Solubility Saturated: The maximum amount of a solute that can be dissolved into a solvent. Unsaturated: less than the maximum amount of solute that can be dissolved. Supersaturated: More dissolved solute than a saturated solution at the same temperature Must be heated, then cooled slowly Very unstable

Solubility Curve The lines represent the different saturation points for different compounds Notice, the solubilities are measured in g/100 g H 2 O Under the line is unsaturated, over the line is supersaturated

Solution Concentration The concentration of a solution is measured in Molarity (M) M = moles / liter M = mol/L (moles of solute per liters of solution) Diluting solutions: M 1 V 1 = M 2 V 2

Practice Problems You have 3.50 L of solution that contains 90.0 g of NaCl. What is the molarity of this solution? Answer: 0.44 M You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl are present? Answer: 0.4 mol HCl What volume of 3.00 M NaCl is needed for a reaction that requires g of NaCl? Answer: L

Dilutions Practice Problems You want to make 2.3 L of a 3.5 M H 2 SO 4 solution. If you only have 12 M sulfuric acid in stock, how much must be added to water to make the solution you need? Answer: In lab you produce 2.5 L of 6 M HNO 3. If you added 0.5 L of a concentrated solution to get this solution, what was the original concentration of the acid?

Molality: Another way to measure concentration. Moles of solute per kilogram of solvent m = mol / kg Notice: solvent must be in kg! Example: A solution was prepared by dissolving 17.1 g of sucrose (C 12 H 22 O 11 ) in 125 g of water. Find the molal concentration. Answer: m

Molality Examples A solution of I 2 in CCl 4 is used when iodine is needed for certain chemical tests. How much iodine must be aded to prepare a m solution of iodine in CCl 4 if g of CCl 4 is used? Answer: 12.2 g of I 2 What is the molality of a solution composed of 255 g (CH 3 ) 2 CO dissolved in 200. g of water? Answer: 22 m