Making/Diluting Solution

Introduction to Solution Preparation

• Focused on converting moles of solute to grams.

• Preparation involved making a point four molar solution of cobalt chlorate hexahydrate, focusing on the understanding of hydrates.

Hydrates

• Definition: Hydrates are compounds that include water molecules integrated into their structure.

• Example: Nickel chloride hexahydrate (NiCl₂•6H₂O).

  • Composition: 1 nickel (Ni), 2 chlorines (Cl), and 6 waters (H₂O).

  • Importance: The need to consider water mass when calculating total molar mass.

Molar Mass Calculation

• Nickel: 59 g/mol

• Chlorine: 35.5 g/mol (2 Cl = 71 g/mol)

• Water: 18 g/mol (6 H₂O = 108 g/mol)

• Total molar mass = 59 (Ni) + 71 (Cl) + 108 (H₂O) = 238 g/mol

Preparing Solutions

• Desired solution: 0.4 M (Molarity) for a volume of 500 mL (0.5 L).

• Calculation to find moles needed:

  • Moles = Molarity × Volume = 0.4 M × 0.5 L = 0.2 moles.

• Convert moles to grams:

  • Mass = moles × molar mass = 0.2 moles × 238 g/mol = 47.6 g.

Technique and Equipment

• Using a mass scale to weigh out 47.6 g of nickel chloride hexahydrate.

• Volumetric flasks used for accuracy with a defined mark, ensuring precise volume measurement (e.g., 500 mL).

  • Importance of volumetric flasks:

    • Designed to allow for a precise meniscus reading, enhancing accuracy in volume measurement.

Dilution Processes

• Understanding dilution as making a less concentrated solution from a more concentrated stock solution.

• Inverse Relationship:

  • Higher concentration = smaller volume of stock needed.

  • Fundamental equation: M1V1 = M2V2, where M = molarity and V = volume.

• Practical Example:

  • Preparing a 0.1 M solution from a 0.4 M stock solution involves taking 1/4 of the stock's volume when adjusting to a final volume.

Spectrophotometry in Lab Activities

• Introduction to spectrophotometers for measuring light absorption and transmittance.

• The experiment focuses on how varying concentrations influence light absorption and transmittance; higher concentration leads to higher absorption and lower transmittance.

Final Notes on Solution Preparation

• Importance of familiarity with concepts rather than mere memorization.

• Steps to prepare solutions include:

  • Determine molar mass needed.

  • Calculate mass of solute from moles.

  • Dissolve and dilute accurately in a volumetric flask or graduated cylinder.

• Students encouraged to practice to become proficient in solution preparations for labs.