Concentration
CALCULATING CONCENTRATION OF SOLUTIONS 1. Mass Percent = (mass of solute/mass of solution)100 2. Parts per million = (mass of solute/mass of solution)106 3. Mass/volume percent = (mass of solute/mL solution)100 4. Volume percent = (mL solute / mL solution)100 5. Molarity = n/V = moles solute / L solution 6. Molality = moles of solute / kg solvent
CALCULATING CONCENTRATION OF SOLUTIONS What is the mass percent of a solution made by adding 25.0 g of KCl to 100.0 mL of water? What is the concentration of a solution made by mixing 25.0 g of KCl in (a) 100.0 mL and (b) 100.0 L of water in ppm?
The following slides are extra worked out examples.
CALCULATING CONCENTRATION OF SOLUTIONS How many grams of a solution that is 32.7% by mass NaCl would contain 45.0 g of NaCl? Mass % = (mass of solute /mass of solution) 100 32.7 % = (45.0 g / x )100 x = 45.0 g / 0.327 x = mass of solution = 138 g
CALCULATING CONCENTRATION OF SOLUTIONS How much solute is present in 756.1 mL of a 14.7% (mass/volume) HCl solution? Mass/volume % = (masssolute/volumesolution) 100 14.7 % = (x / 756.1 mL )100 x = 0.147 (756.1 mL) x = mass of solute = 111g
CALCULATING CONCENTRATION OF SOLUTIONS How many grams of LiF are in 500 mL of a solution that is 18.4% by mass and has a density of 1.197 g/mL? Masssolution = densitysolution (Volumesolution) = 1.197 g/mL (500 mL) = 598.5 g solution Mass% = (masssolute/masssolution) 100 18.4 % = (x / 598.5 g )100 x = 0.184 (598.5 g) x = mass of solute = 110 g
CALCULATING CONCENTRATION OF SOLUTIONS A 350 mL sample of drinking water was analyzed and found to contain 0.0046 g of sulfate salts. Calculate the concentration of sulfate salts in this water sample? Masswater = densitywater (Volumewater) = 1.00 g/mL (350 mL) = 350 g solution ppm = (masssolute/masssolution) 106 ppm = (0.0046g / 350 g ) 106 ppm = 13 ppm Use ppm for trace amounts of solute.
CALCULATING CONCENTRATION OF SOLUTIONS Calculate the molality of a solution composed of 53.0 g of KOH in 500 mL of water. First calculate the moles of solute: n = 53.0 g (1 mol / 56 g) = 0.946 mol solute Next, m = moles of solute / kg solvent m = (0.946 mol / 0.500 kg ) m = 1.89 molal solution
PRACTICE PROBLEMS #36 calculating the CONCENTRATION OF SOLUTIONS ___1. How many grams of a 45.0 % Mg(OH)2 solution can be made from 7.00 g of solid Mg(OH)2? ___2. How many kilograms of a 6.8% KC2H3O2 solution will contain 5.3 moles of KC2H3O2? ___3. How many grams of KOH are needed to make 250.0 mL of a solution that is to contain 6.70 mg/mL of potassium ion? ___4. If 134.5 g of a 25.0 % sucrose solution was prepared, how many grams of a 5.00% solution of sucrose would contain the same amount of sugar? ___5. How many grams of solution, 10.0% KOH by mass, are required to neutralize 25.0 mL of a 2.00 M HCl solution if the moles of HCl is equal to the moles of KOH? 15.6 g 7.6 kg 2.41 g 673 g 28.0 g
Group study problem #36 calculating the CONCENTRATION OF SOLUTIONS ___1 How many grams of a solution, that is 76.3% by mass KBr, would contain 38.95 g of KBr? ___2. What is the ppm and molality of a solution containing 75.0 g of ethylene glycol, C2H6O2, in 200.0 g of water? ___3. How many grams of CuSO4 are needed to make 350.0 mL of a solution that contains 10.5 mg/mL of Cu2+ ion? Calculate the molarity of the resulting solution. ___4. Automobile battery acid is 38% H2SO4 and has a density of 1.29 g/mL. Calculate the molality of this solution. ___5. If 27.0 g of LiBr are dissolved in 50.0 g of water, the percent of LiBr by mass is ___6. If 15.0 g of KNO3 is added to 75g of water, what is the mass percent of KNO3 in the solution?