Quantitative Analysis of Salts

• Electrical Conductivity: Measures salinity level as total dissolved solids; does not distinguish between salts.

• Goal: Determine concentration of specific salts in solutions, e.g., sodium chloride in soup.

Water of Hydration

• Copper(II) Sulfate Crystals: Blue crystals consist of water of hydration that becomes a white powder upon heating.

• Gravimetric Analysis: Technique used to determine amount of water in a salt via mass difference before and after heating.

• Chemical representation: CuSO₄ B7 xH₂O; after heating, it becomes CuSO₄.

• Determine x (number of water molecules) by:

  • Weighing hydrated salt before/after heating.

  • Calculating moles via molar mass.

Molar Ratio Calculation

• Example: 5.00 g CuSO₄ B7 xH₂O heated to 3.19 g CuSO₄.

• Mass of water lost: m(H₂O) = 1.81 g.

• Calculate moles:

  • Moles of anhydrous CuSO₄: rac{3.19}{159.6} = 0.0200 ext{ mol}

  • Moles of water: rac{1.81}{18.0} = 0.101 ext{ mol}.

• Molar ratio: rac{0.101}{0.0200} = 5; thus, CuSO₄ B7 5H₂O.

Mass-Mass Stoichiometry

• Use mass of known substances to find amounts in reactions.

• Steps:

  1. Write balanced equation.

  2. Convert mass of precipitate to moles.

  3. Use stoichiometric ratios to find moles of unknown.

  4. Calculate mass using m = n × M.

Gravimetric Analysis

• Technique for measuring composition/concentration, mainly for salts.

• Involves forming a precipitate, which is dried and weighed.

• Example: Barium ions measured by precipitating with sodium sulfate.

• Standard steps:

  1. Weigh sample.

  2. Dissolve in solvent.

  3. Add solution to form precipitate.

  4. Filter to collect precipitate.

  5. Dry and weigh precipitate.