Concentration

CALCULATING CONCENTRATION OF SOLUTIONS

1. 1. Mass Percent = (mass of solute/mass of Mass Percent = (mass of solute/mass of solution)100solution)100

2. Parts per million = (mass of solute/mass of 2. Parts per million = (mass of solute/mass of solution)10solution)1066

3. Mass/volume percent = (mass of solute/mL 3. Mass/volume percent = (mass of solute/mL solution)100solution)100

4. Volume percent = (mL solute / mL 4. Volume percent = (mL solute / mL solution)100solution)100

5. Molarity = n/V = moles solute / L solution5. Molarity = n/V = moles solute / L solution6. Molality = moles of solute / kg solvent6. Molality = moles of solute / kg solvent

CALCULATING CONCENTRATION OF SOLUTIONS

1.1. What is the mass percent of a solution What is the mass percent of a solution made by adding 25.0 g of KCl to 100.0 made by adding 25.0 g of KCl to 100.0 mL of water?mL of water?

2. 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 The following slides are extra worked out extra worked out examples. examples.

CALCULATING CALCULATING CONCENTRATION OF CONCENTRATION OF

SOLUTIONSSOLUTIONS• How many grams of a solution that is How many grams of a solution that is

32.7% by mass NaCl would contain 32.7% by mass NaCl would contain 45.0 g of NaCl?45.0 g of NaCl?

Mass % = (mass of solute /mass of Mass % = (mass of solute /mass of solution) 100solution) 100

32.7 % = (45.0 g / x )10032.7 % = (45.0 g / x )100

x = 45.0 g / 0.327x = 45.0 g / 0.327

x = mass of solution = x = mass of solution = 138 g138 g

CALCULATING CALCULATING CONCENTRATION OF CONCENTRATION OF

SOLUTIONSSOLUTIONS• How much solute is present in 756.1 How much solute is present in 756.1

mL of a 14.7% (mass/volume) HCl mL of a 14.7% (mass/volume) HCl solution?solution?

Mass/volume % = (massMass/volume % = (masssolutesolute/volume/volumesolutionsolution) ) 100100

14.7 % = (x / 756.1 mL )10014.7 % = (x / 756.1 mL )100

x = 0.147 (756.1 mL)x = 0.147 (756.1 mL)

x = mass of solute = x = mass of solute = 111g111g

CALCULATING CALCULATING CONCENTRATION OF CONCENTRATION OF

SOLUTIONSSOLUTIONS• How many grams of LiF are in 500 mL How many grams of LiF are in 500 mL

of a solution that is 18.4% by mass of a solution that is 18.4% by mass and has a density of 1.197 g/mL? and has a density of 1.197 g/mL?

• MassMasssolutionsolution = density = densitysolutionsolution (Volume (Volumesolutionsolution))

= 1.197 g/mL (500 mL)= 1.197 g/mL (500 mL)

= 598.5 g solution = 598.5 g solution

Mass% = (massMass% = (masssolutesolute/mass/masssolutionsolution) 100) 100

18.4 % = (x / 598.5 g )10018.4 % = (x / 598.5 g )100

x = 0.184 (598.5 g)x = 0.184 (598.5 g)

x = mass of solute = x = mass of solute = 110 g110 g

CALCULATING CALCULATING CONCENTRATION OF CONCENTRATION OF

SOLUTIONSSOLUTIONS• A 350 mL sample of drinking water was A 350 mL sample of drinking water was analyzed and found to contain 0.0046 g of analyzed and found to contain 0.0046 g of sulfate salts. Calculate the concentration sulfate salts. Calculate the concentration of sulfate salts in this water sample?of sulfate salts in this water sample?

• MassMasswaterwater = density = densitywaterwater (Volume (Volumewaterwater))

= 1.00 g/mL (350 mL)= 1.00 g/mL (350 mL)

= 350 g solution = 350 g solution

ppm = (massppm = (masssolutesolute/mass/masssolutionsolution) 10) 1066

ppm = (0.0046g / 350 g ) ppm = (0.0046g / 350 g ) 101066

ppm = ppm = 13 ppm13 ppmUse ppm for trace amounts of solute.Use ppm for trace amounts of solute.

CALCULATING CALCULATING CONCENTRATION OF CONCENTRATION OF

SOLUTIONSSOLUTIONS• Calculate the molality of a solution Calculate the molality of a solution

composed of 53.0 g of KOH in 500 mL of composed of 53.0 g of KOH in 500 mL of water.water.

First calculate the moles of solute:First calculate the moles of solute:

n = 53.0 g (1 mol / 56 g) = 0.946 mol n = 53.0 g (1 mol / 56 g) = 0.946 mol solutesolute

Next, Next, mm = moles of solute / kg solvent = moles of solute / kg solvent

mm = (0.946 mol / 0.500 kg ) = (0.946 mol / 0.500 kg )

mm = = 1.89 molal solution1.89 molal solution

PRACTICE PROBLEMS #36PRACTICE PROBLEMS #36 calculating the CONCENTRATION OF SOLUTIONScalculating 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 g15.6 g

7.6 kg7.6 kg

2.41 g2.41 g

673 g673 g

28.0 g28.0 g

Group study problem #36Group study problem #36 calculating the CONCENTRATION OF SOLUTIONScalculating 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?