Solutions and Units of Concentration May 11, 2015 What is a Mixture? Types of Mixtures Definitions A solution is a homogeneous mixture A solute is dissolved in a solvent. – Solute is the substance being dissolved – Solvent is the liquid in which the solute is dissolved – An aqueous solution has water as solvent Definitions Continued Dilute: a solution with a small amount of solute Concentrated: a solution with a large amount of solute A saturated solution is one where the concentration is at a maximum - no more solute is able to dissolve A super-saturated solution is one where the concentration has more solute than it can normally dissolve Solubility: a measure of how easily a solute dissolves in a solvent Some Examples Solute Solvent Example solid solid Alloys (brass, steel) solid liquid Salt water gas solid liquid liquid Air bubbles in ice cubes Ethanol in water gas liquid Soft drinks gas gas Air Solubility We can measure how easily a solute will dissolve in a certain solvent. This measure is called solubility Dissolution of Solid Solute What are the driving forces which cause solutes to dissolve to form solutions? 1. Covalent solutes dissolve by H-bonding to water 2. Ionic solutes dissolve by dissociation into their ions. Solution and Concentration WAYS OF EXPRESSING CONCENTRATION – Molarity (M) – Molality (m) – Mole Fraction (X) – Mass Percent (%) – Parts Per… (ppm) Molarity (M) moles of solute (n) M= L of solution (V) **concentration of solute per given amount of volume** Concentration measurement Because volume is temperature dependent, molarity can change with temperature Concentration: Molarity Example Calculate the molarity of the following solution: 1) 2.3 moles of sodium chloride in 0.45 liters of solution M = moles of solute = 2.3 moles = 5.11M liters of solution 0.45 liters Concentration: Molarity Example 2) 45 grams of ammonia (NH3) in 0.75 L of solution. First convert grams of NH3 to moles: 45 g / 17 g = 2.65 Moles MM of NH3 Now plug into Molarity equation: M = moles of solute = 2.65 moles = 3.53M liters of solution 0.75 liters Concentration: Molarity Example 3) What mass of LiOH would you mass to make a 5.0 liter of 2.06 M solution First find how many moles 5.0 L would be: M=n 2.06 M = n V 5.0 L n = 10.3 moles Now find the mass of 10.3 moles: mass = Moles x molar mass LiOH mass = 10.3 Moles x 23.95 g/M mass = 246.7 grams NOW YOU TRY 1) 0.09 moles of sodium sulfate in 12 mL solution. (1000 mL = 1 L) 0.09 Moles / .012 L = 7.5 M 2) 0.75 moles of lithium fluoride in 65 mL of solution. (1000 mL = 1 L) 0.75 Moles / .065 L = 11.54 M