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Concentrations

Concentrations. Concentration units. Concentration of any solution is expressed in terms of the amount of solute dissolved in one unit of the solvent or solution. The amount of solute dissolved in one unit of the solvent or solution – concentration. Expressing concentration. Percentage

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Concentrations

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  1. Concentrations

  2. Concentration units • Concentration of any solution is expressed in terms of the amount of solute dissolved in one unit of the solvent or solution. • The amount of solute dissolved in one unit of the solvent or solution – concentration.

  3. Expressing concentration • Percentage • Wt % of solute = wt of solute/vol. of solution x 100 • Wt % of solute = wt of solute/w of solution x 100 • Vol. % of solute = v of solute/v of solu x 100

  4. Expressing concentration 2. Parts Per Million (ppm) Parts per million of the solute (ppm) = w of solute/w of solution x 106 (if 2g of solute is present in 106 g of solution, its concentration is 2 ppm.

  5. Expressing concentration 3. Molarity (M) Molarity of a solution is defined as the number of moles of the solute dissolved per litre of solution. M = No. of moles of solute/vol. of solution in litres = n/V If W g of a substance having molar mass M, is dissolved in V dm3 of solution, then the molarity (M) = W/MxV mol dm-3

  6. Expressing concentration 4. Formality – no. of formula weights dissolved per litre of the solution: F = no. of formula mass of solute/vol. of solution in litres F = Mass of solute/ formula mass of solute x V of solution

  7. Expressing concentration 5. Normality – defined as the number of equivalents of the solute dissolved per litre of solution. • Normality (N) = no. of equivalents of solute/ vol of solution • N = Mass of solute (W)/ Equivalent mass of solute (E) x Vol of solution (V) • N = W/E x V equiv dm-3

  8. Expressing concentration 6. Molality – defined as number of moles of solute per kg of the solvent. • If solution prepared by dissolving n moles of the solute in W kg of the solvent, then Molality (m) = no. of moles of solute/ mass of solvent in kg = n/W mol per kg or Mass of solute(w)/Molar mass of solute(M) x Mass of solvent in kg or m = w/MxW mol kg-1

  9. Expressing concentration 7. Mole fraction (X) – ratio of the number of moles of that component to the total number of moles of all the components of the solution. Thus, if a solution contains nA moles of A and nB moles of B, then, mole fraction of A (XA) = no. of moles of A/ no. of moles of A + no. of moles of B or XA= nA/nA+ nB. Sum of mole fraction of all the components of a solution = 1.

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

  11. Activity • What is the molarity of an aqueous solution of ethanoic acid, molar mass = 60, which contains 6.0 g of ethanoic acid in 500 ml of solution? • Calculate the molality of one litre of 93% H2SO4 solution (W/V). The density of the solution is 1.84 g per ml.

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