Solution Composition

1
SolutionComposition Concentration

• Mass Percent Molarity!

2
Mass

• Describes the composition of a solution.
• a.k.a. weight percent
• Mass mass of solute x 100
• mass of solution
• grams of solute x
  100
• grams of solute grams of solvent

3
Mass example

• A solution is prepared by dissolving 1.0g of
  sodium chloride in 48g of water. Calculate the
  percent mass of the solution!
• 1.0 g of solute
• Total mass of solution is 49g (1.0g of
  solute 48g of solvent)
• 1.0g solute x 100 2.0 NaCl
• 49 g solution

4
Try this one

• Cows milk typically contains 4.5 by mass of
  lactose (C12H22O11). Calculate the mass of
  lactose present in 175g of milk.
• 7.9g lactose

175 g milk X 0.045
5
Molarity, M

• Describes the solution concentration in terms of
  volume
• rather than composition in terms of mass (its
  much more convenient to measure the volume of a
  liquid!)
• M Molarity moles of solute mol
• liters of solution L
• Ex/ a solution that contains 1.0 mol of solute
  per Liter of solution is 1.0M 1.0 molar

6
Molarity example

• A solution is prepared by dissolving 11.5g of
  solid NaOH in enough water to make a 1.50L
  solution. (The solute and solvent together have
  a volume of 1.50L) Calculate the Molarity.
• Mass of solute 11.5 g NaOH ? convert to moles!
• 11.5g NaOH x 1 mol NaOH 0.288 mol NaOH
• 40.0g NaOH
• Volume of solution 1.50L
• Molarity 0.288 mol NaOH 1.92 M NaOH
• 1.50 L solution

7
Try this one

• What mass of solid potassium dichromate (K2Cr2O7)
  must be weighed out to make 1.00 L of a 0.200 M
  solution? (molar mass 294.2)
• 58.8 g potassium dichromate

Algebra g (molar mass)(molarity)(volume)
8
Standard Solutions

• A solution with an accurately known concentration
• Prepared in a volumetric flask
• Vol. flasks measure volume extremely accurately
• Solute is weighed and completely added to vol.
  flask
• Solvent is added to flask to bring volume up to
  exact volume line on neck of flask

9
How to make a solution of a given molarity.

• 1. Calculate the grams needed g (mm)(M)(L)
• Measure out that exact amount.
• Rinse into mL volumetric flask.
• Fill 2/3 s full with distilled water.
• Swirl to dissolve.
• Fill to line with distilled water.
• Cap and flip 20 times.
• Label M(what it is), date , who made
  it