Molarity

1
Molarity

• Moles/Liter

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Concentration
Strength of an acid or base is determined by the
amount of ionization. Concentration is
determined by the amount of water added to the
substance. Molarity (M) The number of moles of
solute dissolved in each liter of
solution. Molarity moles of solute
liters of solution
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Example Problem 1

• If 1.00 liter of sugar water contains exactly
  1.00 mole of sugar, what is its molarity?
• Molarity 1.00 mol
• 1.00 L
• Molarity 1.00 M

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Example Problem 2

• If 1.00 liter of sugar water contains exactly
  2.00 mole of sugar, what is its molarity?
• Molarity 2.00 mol
• 1.00 L
• Molarity 2.00 M or 2.00 mol/L
• (Twice as concentrated)

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Example Problem 3

• What is the molarity when 0.75 mol is dissolved
  in 2.50 L of solution?
• Molarity 0.75 mol 0.30 mol/L or 0.30M
• 2.50 L

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In Lab, grams are typically used in place of
moles.

• If you wanted to make 2.00L of a 6M HCl
  solution, how much HCl would you need?
• First, calculate the molar mass of the acid.
• H 1 x 1.00795 1.00795
• Cl 1 x 35.453 35.453
• 36.46095 36.461

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If you wanted to make 2.00L of a 6M HCl
solution, how much HCl would you need?

• First, calculate the molar mass of the acid.
• HCl contains 36.461 g/mol
• It would take 36.461 g of HCl to make 1 liter of
  a 1M HCl solution. How many grams would it take
  to make 2L of a 1M solution?
• 2 x 36.461g 72.922g

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If you wanted to make 2.00L of a 6M HCl
solution, how much HCl would you need?

• It takes 72.922g of HCl to make 2 liters of a 1M
  solution. How much would it take to make 2
  liters of a 6M solution?
• 6 x 72.922g 437.532 g

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Try One More

• Suppose you wanted to make 2 liters of a 0.5 M
  solution of HCl. How much HCl would you need?
• Each mole of HCl is equal to 36.461g
• For a 0.5 M solution, you would need half that
  much. 36.461 x 0.5 18.2305g.
• However, you want to make 2 liters, so double
  that amount. 18.2305 x 2 36.461g.