• SEPARATING SOLUTIONS• CONCENTRATIONS AND MOLARITY• SOLUBILITY AND DISSOLVING

Solutions

Concentration

Concentration – the amount of particular substance in a given quantity of a solution.

Concentration can be expressed in many forms: ppm – parts per million molarity – moles solute over liters solution molality – moles solute over kg of solvent

We can make these calculations if we know the quantity of solute and volume (quantity) of solvent.

Molarity

We often use molarity when dealing with concentrations.

Molarity – a concentrations unit of a solution expressed as moles of solute dissolved per liter of solution.

How MUCH solute is in how MUCH solvent

M = mol / L

Molarity

Molarity describes a solution in terms of volume of solution not volume of solvent.

If you need 1 Liter of solution, you are NOT adding 1 Liter of solvent. You must add “enough” solvent to make the total volume 1 Liter. The solute will take up some of the volume.

You can determine the number of moles of solute if you know the mass used.

Practice Problems

What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl?

Practice on your own

Vinegar contains 5.0 g acetic acid, CH3COOH, in 100.0 mL of solution. Calculate the molarity of the acetic acid in the vinegar.

What mass of KCl is present in 25 mL of a 0.85 M solution of potassium chloride?

Solution Stoichiometry

Solutions of known concentrations are often used in the lab.

When reactions involving these solutions occur, we can use stoichiometry to calculate the mass of products we should obtain.

We could then use this amount of product formed along with the total volume of the system to determine the concentration of product formed.

Soln. Stoich. Practice

An excess of zinc is added to 125 mL of 0.100 M HCl solution. What mass of zinc chloride is formed?

___ Zn + ___ HCl ___ ZnCl2 + ___H2

Soln. Stoich. Practice

What volume (in milliliters) of a 0.500 M solution of copper (II) sulfate is needed to react with an excess of aluminum to provide 11.0 grams of copper? Hint: Step 1: Write out and balance your reaction

Work on Solution Stoich WKST – Due tomorrow

Vocab Sheet due Friday