Solution Concentration (Molarity)

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Solution Concentration (Molarity)
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Concentration

• a measure of the amount of solute that is
  dissolved in a given quantity of solvent
• unit of measurement is Molarity (M) which is
  moles/liter
• can be dilute or concentrated

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Molarity

• The number of moles of solute dissolved in one
  liter of solution

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1.0 L of water was used to make 1.0 L of
solution. Notice the water left over. 1.0L of
water would be too much.
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Making a known molar solution
top off to 1 liter
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PROBLEM Dissolve 5.00 g of NiCl26 H2O in
enough water to make 250 mL of solution.
Calculate the Molarity.
Step 1 Calculate moles of NiCl2 6H2O in 5 g of
NiCl2 6H2O
1.0 L 1000 mL .25 L 250 mL
Step 2 Calculate Molarity
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USING MOLARITY
What mass of oxalic acid, H2C2O4, is required to
make 250 mL of a 0.0500 M solution?
M moles/V ? moles MV

• Step 1 Change mL to L.
• 250 mL/1000 0.250 L
• Step 2 Calculate.
• moles (0.0500 M) (0.250 L) 0.0125 moles
  H2C2O4
• Step 3 Convert moles to grams.
• (0.0125 mol H2C2O4) (90.00 g) 1.13 g
• 1 mol
  H2C2O4

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Learning Check

• How many grams of NaOH are required to prepare
  400 mL of 3.0 M NaOH solution?
• 1) 12 g
• 2) 48 g
• 3) 300 g

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Making Dilutions

• diluting a solution reduces the number of moles
  of solute per unit volume, but the total number
  of moles of solute in the solution does not
  change
• therefore, as Volume increases, Molarity
  decreases
• Molarity (M) moles of solute
• liters of solution (V)
• becomes M1 V1 M2 V2

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How many milliliters of a 2.00M MgSO4 solution
must be diluted with water to prepare 100 ml of a
0.400 M MgSO4 solution?
M1 V1 M2 V2
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air
lead
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Percent Solutions

• another way to quantitatively describe the
  concentration of a solution (two ways)
• the ratio of the volume of the solute to the
  volume of the solution
• V volume of solute / volume of solution x
  100
• 85 mL of ethanol diluted with water to a total
  solution volume of 250mL
• 85 mL/250 mL (100) 34 ethanol by volume
• the ratio of the mass of the solute to the mass
  of the solution
• M mass of solute / mass of solution x 100
• 56 g NaCl in a 2000 g NaCl solution
• 56g/2000g (100) 2.8 salt by mass