Solutions and Units of Concentration FUNDAMENTALS May 11, 2015

What is a Mixture?

Types of Mixtures

Definitions n A solution is a homogeneous mixture n A solute is dissolved in a solvent. –solute is the substance being dissolved –solvent is the liquid in which the solute is dissolved

Definitions Continued n Dilute: a solution with a small amount of solute n Concentrated: a solution with a large amount of solute n A saturated solution is one where the concentration is at a maximum - no more solute is able to dissolve n A super-saturated solution is one where the concentration has more solute than it can normally dissolve n Solubility: a measure of how easily a solute dissolves in a solvent

Some Examples SoluteSolventExample solid Alloys (brass, steel) solidliquidSalt water gassolidAir bubbles in ice cubes liquid Ethanol in water gasliquidSoft drinks gas Air

Solubility n We can measure how easily a solute will dissolve in a certain solvent. n 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.

moles of solute L of solution M = n Concentration of moles of solute per given amount of volume n Concentration measurement n Because volume is temperature dependent, molarity can change with temperature Concentrations: MOLARITY (M) n (moles) M V (liters)

Concentration: Molarity Example #1 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 liters of solution 0.45 M = [ 5.11 M ] n (moles) M V (liters)

Concentration: Molarity Example #2 Calculate the molarity of the following solution : 2) 10.3 moles of LiOH in 250 mL in solution. **Need to convert mL to L (÷ by 1000) M = moles of solute = 10.3 moles = 41.2M liters of solution liters

Concentration: Molarity Example #3 Calculate the moles of the following solution : 3) How many moles are needed to make 2 L of a [5.5 M] solution of NaOH? M = n (moles) V (liters) [5.5M] = n (moles) 2 Liters n = 5.5 x 2 = 11 moles n (moles) M V (liters)

Concentration: Molarity Example #3 Calculate the moles of the following solution : 3) How many grams is this? Need MOLAR MASS of NaOH: 40 grams n = 11 moles 11 moles x 40 g = 440 g n (moles) M V (liters) Na: 23 g O: 16 g H: 1 g TOTAL: 40g