Molarity By: Gurpreet Dulay & Kiranjit Kandola

Some definitions The CONCENTRATION of a substance in solution is the amount of the substance which exists in a given volume of the solution A CONCENTRATED solution has a relatively high concentration (large amount of substance dissolved in a solution) A DILUTE solution has a relatively low concentration (very little substance is dissolved in the solution)

What is Molarity? The of a substance in a solution that is the number of moles of the substance contained in 1 L of solution The MOLAR CONCENTRATION of a substance in a solution that is the number of moles of the substance contained in 1 L of solution Molar concentration is also known as Molar concentration is also known as MOLARITY The unit symbol for “mol/L” is “M” The unit symbol for “mol/L” is “M” 1 mole is 6.02 x 10 ²³ 1 mole is 6.02 x 10 ²³

Molar concentration = Moles Volume or : c = n v Where:c = molar concentration, in mol/L n = number of moles v = volume, in liters How to find molar concentration

How to Prepare a Standard Solution Weigh 0.58 NaCl Weigh 0.58 NaCl Add NaCl to 80mL of water Add NaCl to 80mL of water Stir solution until salt is dissolved Stir solution until salt is dissolved Pour solution into 100 mL grad. cylinder Pour solution into 100 mL grad. cylinder Bring the solution up to 100 mL Bring the solution up to 100 mL

Calculations: Moles, Volume, and Molarity 1) How many moles of AlCl 3 are contained in mL of 0.250M AlCl 3 ? moles AlCl 3 = mol x L = mol L 2) What volume of 2.40 M HCl can be made from g of HCl? moles of HCl = 100.0g x 1 mol = 2.74 mol 36.5 g 2.74 mol = 1.14 L 2.40 mol/L 2.40 mol/L 3) What is the molarity of the CaCl2 in a solution made by dissolving and diluting g of CaCl2 x 6H2O [CaCl2]=[CaCl2 x 6H2O] = 15.00g x 1 mol = M L 219.1g L 219.1g

Dilution Calculations The formula for dilution calculations is: The formula for dilution calculations is: M I V I = M F V F Where M I is the initial molarity V I is the initial volume M F is the final diluted molarity V F is the final volume

Dilution calculation example: A chemist starts with 50.0 mL of a 0.40 M NaCl solution and dilutes it to 1000 mL of water. What is the concentration of NaCl in the new solution? 50.0 mL of 0.40 M NaCl mL water

STEPS: You multiply the two intials together: (0.40 M) (50.0 mL) = (M F ) (1000. mL) (0.40 M) (50.0 mL) = (M F ) (1000. mL) Then you use basic algebra to isolate the M F (0.40 M) (50.0 mL) (1000. mL) = (M F ) (0.40 M) (50.0 mL) (1000. mL) = (M F ) Final answer: M = M F M = M F

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