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.
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.
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
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.
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.
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.
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.
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.