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Molar Concentration

Molar Concentration. CHEMISTRY 11 April 12, 2010. Molar Concentration or “Molarity”. Molar concentration refers to the number of moles of a solute in a given volume of solution. It is also called “molarity” Molar concentration has units of moles solute per litre solvent = mol/L = M

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Molar Concentration

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  1. Molar Concentration CHEMISTRY 11 April 12, 2010

  2. Molar Concentration or “Molarity” • Molar concentration refers to the number of moles of a solute in a given volume of solution. It is also called “molarity” • Molar concentration has units of moles solute per litre solvent = mol/L = M • 2 mol NaCl dissolved in 1.00 L of water gives a 2 mol/L solution of NaCl in water • 2 M NaCl(aq) solution

  3. Solving Problems with Molar Concentration • Must calculate total moles and total volume • Divide moles by volume = mol/L • Concentration × volume = moles • Concentration = moles / volume

  4. Basic Molarity Problems • 1. If you dissolve 5.01 mol of NaCl in 100 mL of water, what is the molar concentration of the NaCl solution? • 2. If you have 75 mL of a 0.500 M CaCl2 solution, how many moles of CaCl2 do you have? • 3. What volume of 1.40 M KOH is needed to have 1.00 mol of KOH?

  5. Answers • 5.01 mol / 0.100 L = 50.1 mol/L = 50.1 M • 0.500 M CaCl2 × 0.075 L = 0.0375 mol CaCl2 • 1.00 mol × (1 L / 1.40 mol) = 0.714 L • = 714 mL

  6. Basic Molarity Problems • 4. You have 600 mL of 1.50 M HCl solution. Using water, you dilute the solution up to a volume of 1.00 L. What is the new concentration of the solution? • 5. You have 300 mL of 0.800 M KOH in one beaker and 250 mL of 0.700 M KOH in another beaker. If you mix the two solutions, what is the molarity of the resulting solution?

  7. Answers • 1.50 mol/L HCl × 0.600 L = 0.900 mol HCl • 0.900 mol HCl / 1.00 L = 0.900 mol/L HCl • 0.800 M × 0.300 L = 0.240 mol KOH • 0.700 M × 0.250 L = 0.175 mol KOH • 0.415 mol KOH • 0.415 mol KOH in total volume of • 0.250 L + 0.300 L = 0.550 L • Final concentration is 0.415 mol KOH / 0.550 L • = 0.755 M KOH

  8. Mole Bridge Problems • Because we are dealing with moles, any question concerning molar concentration can be extended into mole bridge types of questions • Step 1: Convert concentrations to moles • Step 2: Solve mole bridge problem • HEBDEN p. 131, q. 17 • Let’s try it together!

  9. HOMEWORK • HEBDEN p. 131, qq. 17-19

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