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.

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