ChemAtlas

Chapter 9

Solutions

Concentration says how much solute sits in how much solution. Molarity counts in moles, percent counts in grams, and parts per million counts what is barely there at all.

Stock12 M · 25 mLadd waterDiluted3 M · 100 mLM₁V₁ = M₂V₂12 × 25 = 3 × 100300 = 300 ✓The moles of solutenever changed.
Fig. 6Dilution adds solvent but not solute. The same red particles are spread through more liquid, which is exactly why M₁V₁ = M₂V₂ holds.
Solve for
M
g
L

Watch the volume

Molarity uses the volume of the finished solution, not the volume of solvent you started with. Dissolving changes the volume, which is why you make up to the mark rather than adding a litre of water.

Molarity

0.99995mol/L

Moles of solute

0.99995mol

Mass needed

58.44g

Volume

1L

Working

  1. 01Molar mass of NaCl58.4427 g/mol
  2. 0258.44 g × (1 mol / 58.4427 g)0.999954 mol
  3. 03M = mol ÷ L = 0.999954 ÷ 10.999954 M
  4. 040.999954 mol × (58.4427 g / 1 mol)58.44 g
  5. 05Reported to 1 significant figure, set by 1. Conversion factors and balanced coefficients are exact and do not limit the answer.