Solutions Homogeneous mixture = solution Solute the substance that’s being dissolved Solvent - the substance that the solute is dissolved in.

Types Gas/gas Gas/liquid Liquid/liquid Solid/liquid Air is 78% N 2 and 21% O 2 Carbonated sodas are made by dissolving CO 2 gas in water Vinegar is 5% acetic acid, 95% water Sports drinks are 0.1% NaCl, 5% sugar and 94.9% water. Examples Which one is the solvent and which one is the solute?

How much will dissolve? Saturated solution: No more solute will dissolve. Unsaturated solution: Haven’t added enough solute to the solvent for the solution to be saturated. If more solute is added, it will dissolve. Supersaturated solution: Have ‘tricked’ the solution so that there is more solute dissolved in the solvent than is present in a saturated solution. Adding more solute causes the excess solute to precipitate out of solution.

Solubility curves Plots the MAXIMUM number of grams of a solute that will dissolve in 100 g of the solvent at particular temperatures.

2. Is a solution containing 80 g of NH 4 Cl at 80 o C saturated, unsaturated or supersaturated? 1. Is NaNO 3 or KNO 3 more soluble at 50 o C?

4. Is a solution containing 80 g of KNO 3 at 80 o C saturated, unsaturated or supersaturated? Ce 2 (SO 4 ) 3 3. What is least soluble at 40 o C? 5. At what temp. will crystals appear for the solution in #4? 50 o C

Temperature effects If the solute is a liquid or a solid, solubility increases as temperature increases. TemperatureSolubility as

Solubility of gases As the TEMPERATURE INCREASES, the SOLUBILITY of the gas DECREASES. This is because the intermolecular forces between the gaseous solute and the solvent decrease with increased thermal motion. As the PRESSURE of the gas ABOVE THE SOLVENT INCREASES, the SOLUBILITY of the gas INCREASES. The relationship between pressure and gas solubility is given by Henry’s Law (yes, another named gas law )

Solution concentration calculations Mass% (m/m) = Example: What is the m/m% of NaCl if 5 g of NaCl is dissolved in 95 g of water? 5% by mass Volume% (v/v) = Example: What is the v/v% if 20 mL of ethanol is dissolved into 80 mL of water? 20% by volume Mass/Volume% (m/v) = Example: What is the m/v% if 15 g of NaCl is dissolved into 100 mL of water? 15% mass/volume

Mole Fraction: If substance A is the solute and substance B is the solvent, the concentration of both can be expressed in terms of their relative number of moles. Example: A solution of hydrochloric acid contains 1.03 mol HCl and 3.47 mol water. What is the mole fraction for both substances?

Molarity = Example 1: What is the molarity of a solution prepared by dissolving 1.5 mol NaOH in 500 mL of water? Example 2: How could 1.5 L of a 2.5 M solution of NaCl be prepared? Step 1: Calculate how many moles of NaCl are needed M = n/Vn = MVn = (2.5 M)(1.5 L) n = 3.75 moles of NaCl Step 2: Calculate the weight of 3.75 mol NaCl M = V n 3.75 mol NaCl x g/mol NaCl = g NaCl

Solution Dilution Concentrated hydrochloric acid is 12 M. How could 1.5 L of 2.5 M HCl be prepared?  The key principle behind the ‘magic equation’ for dilution is that the number of moles of HCl is conserved…we’re just increasing the amount of water. M 1 V 1 = M 2 V 2 M 1 = 12 M V 1 = ? M 2 = 2.5 M V 2 = 1.5 L (12 M)V 1 = (2.5 M)(1.5 L) V 1 = L Ans: Dissolve L of concentrated HCl in L of water to give a total volume of 1.5 L of 2.5 M HCl.

Definitions: Electrolytes: solutions in which the solutes are ions. Electrolyte solutions will conduct electricity. Nonelectrolytes: solutions in which the solutes are molecules and NOT ions. Nonelectrolytes will NOT conduct electricity.