MolarityBy: Gurpreet Dulay & Kiranjit Kandola

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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 The MOLAR CONCENTRATION of a substance in of a substance in

a solution that is the number of moles of the a solution that is the number of moles of the substance contained in 1 L of solutionsubstance 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 101 mole is 6.02 x 10²³²³

Molar concentration = Moles Volume

or : c = n v

Where: c = molar concentration, in mol/Ln = number of molesv = volume, in liters

How to find molar concentration

How to Prepare a Standard Solution

Weigh 0.58 NaClWeigh 0.58 NaCl Add NaCl to 80mL of waterAdd 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 mLBring the solution up to 100 mL

Calculations:Moles, Volume, and

Molarity1) How many moles of AlCl1) How many moles of AlCl33 are contained in 350.0 mL of 0.250M AlCl are contained in 350.0 mL of 0.250M AlCl33??

moles AlClmoles AlCl33 = 0.250 = 0.250 molmol x 0.3500 L = x 0.3500 L = 0.0875 mol0.0875 mol LL

2) What volume of 2.40 M HCl can be made from 100.0 g of HCl?2) What volume of 2.40 M HCl can be made from 100.0 g of HCl?

moles of HCl = 100.0g x moles of HCl = 100.0g x 1 mol1 mol = 2.74 mol = 2.74 mol 36.5 g 36.5 g 2.74 mol 2.74 mol = = 1.14 L1.14 L

2.40 mol/L2.40 mol/L3) What is the molarity of the CaCl2 in a solution made by dissolving and 3) What is the molarity of the CaCl2 in a solution made by dissolving and diluting 15.00 g of CaCl2 x 6H2O diluting 15.00 g of CaCl2 x 6H2O

[CaCl2]=[CaCl2 x 6H2O] = [CaCl2]=[CaCl2 x 6H2O] = 15.00g15.00g x x 1 mol1 mol = = 0.1369 M0.1369 M

0.5000 L 219.1g0.5000 L 219.1g

Dilution CalculationsThe formula for dilution calculations The formula for dilution calculations

is:is:MMII V VII = M = MFF V VFF

Where Where MMI I isis the initial molaritythe initial molarity

VVII is the initial volumeis the initial volume

MMFF is the final diluted molarityis the final diluted molarity

VVFF is the final volumeis the final volume

Dilution calculation example:

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

50.0 mL of 0.40 M NaCl 1000. mL water

STEPS:

You multiply the two intials together:You multiply the two intials together:

(0.40 M) (50.0 mL) = (M(0.40 M) (50.0 mL) = (MFF) (1000. mL)) (1000. mL)

Then you use basic algebra to isolateThen you use basic algebra to isolatethe Mthe MFF

(0.40 M) (50.0 mL)(0.40 M) (50.0 mL)(1000. mL)    = (M(1000. mL)    = (MFF))

Final answer:Final answer:0.020 M = M0.020 M = MFF

THE END