12.3 Concentration of Solutions

Chemistry II Mr. Jones

concentration

the measure of the amount of solute in a given amount of solvent or solution

Molarity (M)

n/L

• n = moles of SOLUTE

• L = volume of SOLUTION

Molality (m)

n/kg

• n = moles of SOLUTE

• L = volume of SOLVENT

Preparing a “Molal” Solution

1. measure the required amount of grams of solute

2. measure 1.0 kg of solvent in a separate container

3. blend both in a third container

Preparing a “Molar” Solution

1. measure the desired amount of solute in grams in a beaker

2. add solvent to THIS container and mix to dissolve solute, then pour in the volumetric flask

3. rinse the beaker with more solvent and add to the flask

4. agitate the flask

5. add solvent to the volumetric flask to the mark stopper and invert the flask 10 times

Dilutions

• if a solution of known concentration and volume has been diluted, we can calculate the new concentration

• M₁V₁ = M₂V₂

  • M = Molarity

  • V = volume (L)

• M↑ V↓ and M↓ V↑