Concentration

 Distinguish between dilute and concentrated.  Calculate molarity.  Describe how to prepare solutions of given concentrations.  Calculate volume of solvent or mass of solute required to yield a given molarity.

A concentrated solution has a lot of solute as compared to solvent. A dilute solution has little solute as compared to solvent.

% w/w - grams of solute in 100 g of solution. % w/v - grams of solute in 100 mL of solution. 1. Water/air quality: Parts per million (ppm) Number of particles of solute for every million particles solvent. 2. Industrial and household solutions: 3.Medical: g/L Describes quantities of solutes, like cholesterol or sugar in the blood/urine

Concentration units in chemistry: mol/L- moles of solute in one Litre of solution. Known as molarity Molar concentration = Moles of solute Litres of solution n V M=

Calculate the concentration of a NaCl solution if moles is dissolved in 250 mL of solution M (pronounced "mol-er") 250 mL 1000 mL = 0.25 L 1 L 0.25 L = 0.80 mol/L mol n V M=

What volume of a 1.25 M solution contains 5.00 moles of solute? = 4.00 L n V M= 5.00 mol 1.25 M V = 5.0 mol 1.25 mol = 4.00 L 1 L

How many moles of solute needed to make 400 mL of a M solution? n V M= = 0.09 mol n = (0.4)(0.225) 1 L mol 400 mL 1000 mL 1 L = 0.09 mol

= mol What mass of sodium chloride is needed to make L of a M solution? NaCl = 58.5 g/mol n V M= = (0.250)(0.100) mol g = 1.46 g 1 mol 58.5 g L 1 L 0.1 mol

What is the molar concentration of a solution of copper (II) sulfate if 50.0 g is dissolved in 600 mL of solution? CuSO 4 = g/mol 50.0 g g mol 0.6 L = 0.5 M mol n V M= = 0.6 L 50.0 g g 1 mol

Preparing a Solution

To make a solution follow a few basic steps: 1. Determine the mass of the solute needed. 2. Add the solid to a flask or beaker. Adding solute will change the volume of the solvent. 3. Pour in half the solvent and swirl to dissolve. 4. Add solvent to the right volume. 5. Mix the solution further.

Describe the steps needed to make mL of a 0.50 M solution of sodium hydroxide. i. Mass out 10.0 g of NaOH. ii. Add the solid to a 500 mL volumetric flask. iii. Fill the flask half-full with water and swirl until dissolved. iv. Fill the flask to the 500 mL mark, continue to mix. n V M= = (0.500)(0.50) = 0.25 mol mol g = 10.0 g

Concentration of Ions + -

What is the [Cl - ] in M solution of aluminum chloride? Al +3 (aq) + Cl -1 (aq) AlCl 3 (s) mol AlCl 3 1 = L mol Cl - M Cl - 1mol AlCl 3

mol NO 3 - mol Cu(NO 3 ) 2 Cu(NO 3 ) 2 (s) Cu 2+ (aq) + 2 NO 3 ¯ (aq) What mass of copper (II) nitrate is needed to make 2.50 L of a solution that has a nitrate ion concentration of M? 0.25 mol NO g n V M= = (2.50)(0.100) = 0.25 mol NO 3 - = 23.4 g Cu(NO 3 ) 2 mol NO 3 - mol Cu(NO 3 ) L NO g 1 L 0.1 mol

 concentrated - large amount of solute to solvent.  dilute -small amount of solute to solvent.  Concentration is moles of solute in Litres of solution.  The molar concentration is known as molarity, M.