Ways of Expressing Concentrations of Solutions

Mass PercentageMass % of A = 100

Parts per Million andParts per Billionppm = 106Parts per Million (ppm)Parts per Billion (ppb)ppb = 109

Mole Fraction (X)In some applications, one needs the mole fraction of solvent, not solutemake sure you find the quantity you need!

Molarity (M)Because volume is temperature dependent, molarity can change with temperature.

Molality (m)Because neither moles nor mass change with temperature, molality (unlike molarity) is not temperature dependent.

Changing Molarity to MolalityIf we know the density of the solution, we can calculate the molality from the molarity, and vice versa.

PRACTICE EXERCISE(a) Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2500 g of bleaching solution?PRACTICE EXERCISEA commercial bleach solution contains 3.62 mass % NaOCl in water. Calculate (a) the molality and (b) the mole fraction of NaOCl in the solution.

Ideal solutionsNon-ideal solutionsPositive deviation from Raoults lawNegative deviation from Raoults law1.Obey Raoults law at every range of concentration. 2.Hmix= 0; neither is evolved nor absorbed during dissolution.

3.Vmix= 0; total volume of solution is equal to sum of volumes of the components.

4.P = pA + pB = pA0XA+ pB0XB i.e., pA= 1.Do not obey Raoults law.

2.Hmix>0. Endothermic dissolution; heat is absorbed.

3.Vmix> 0. Volume is increased after dissolution.

4.pA> pA0XA; pB> pB0XB pA+ pB> pA0XA+ pB0XB1.Do not obey Raoults law.

2.Hmix

Ideal solutionsNon-ideal solutionsPositive deviation from Raoults lawNegative deviation from Raoults law

5.AA, AB, BB interactions should be same, i.e., A and B are identical in shape, size and character.

6. Escaping tendency of A and B should be same in pure liquids and in the solution. Examples: dilute solutions; benzene + toluence: n-hexane + n-heptane; chlorobenzene + bromobenzene; n-butyl chloride + n-butyl bromide. 5.AB attractive force should be weaker than AA and BB attractive forces. A and B have different shape, size and character.

6. A and B escape easily showing higher vapour pressure than the expected value. Examples: acetone + ethanol acetone + CS2; water + methanol; water + ethanol; CCl4+ toluene; CCl4+ CHCl3; acetone + benzene; CCl4+ CH3OH; Cyclohexane + ethanol 5. AB attractive force should be greater than AA and BB attractive forces. A and B have different shape, size and character.

6. Escaping tendency of both components A and B is lowered showing lower vapour pressure than expected ideally. Examples: acetone + aniline; acetone + chloroform; CH3OH + CH3COOH; H2O + HNO3; Choloroform + diethyl ether, water + HCl; acetic acid + pyridine; chloroform + benzene.

PRACTICE EXERCISE(a) Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2500 g of bleaching solution?Answers:(a) 2.91%, (b) 90.5 g of NaOClAnswers: (a) 0.505 m, (b) 9.00 103

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