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Section 4.5

Section 4.5. Concentrations of Solutions. Concentration. Amount of solute dissolved in a given quantity of solvent or solution Amount of solute = Concentration. Concentration of a solution. moles of solute. Molarity ( M ) =. volume of solution in liters. Molarity (M).

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Section 4.5

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  1. Section 4.5 Concentrations of Solutions

  2. Concentration • Amount of solute dissolved in a given quantity of solvent or solution • Amount of solute = Concentration

  3. Concentration of a solution moles of solute Molarity (M) = volume of solution in liters Molarity (M)

  4. SAMPLE EXERCISE 4.11 Calculating Molarity Calculate the molarity of a solution made by dissolving 23.4 g of sodium sulfate (Na2SO4) in enough water to form 125 mL of solution. Solve: The number of moles of Na2SO4 is obtained by using its molar mass: Converting the volume of the solution to liters:

  5. Concentration of Electrolytes • For ionic compounds: • Look at chemical formula for relative concentration of ions • Ex 1: 1.0M NaCl is 1.0M Na+ and 1.0M Cl- • Ex 2: 1.0M Na2SO4 is 2.0 M Na+ and 1.0M SO42-

  6. Dilution Process of lowering the concentration of a solution by adding water

  7. Dilution Problem • We want: 250.0 mL of 0.100 M CuSO4 • We have: 1.00M CuSO4 Moles solute before dilution = Moles after Mol CuSO4 in dil soln = 0.250L soln x 0.100mol CuSO4 L soln = 0.0250 mol CuSO4 Liters of conc soln = (0.0250 mol CuSO4) x 1 L soln 1.00mol CuSO4 = 0.0250 L Pipet 0.0250L conc sol add dilute it to 250.0 mL

  8. Quick Calculation M conc x V conc = M dil x V dil Why can we ignore moles in dilution problems?

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