Solution Preparation

Mole - A counting term in chemistry representing 6.022 x 10²³ entities, used for measuring amounts of substances.

Concentration and Molarity

• Concentration is expressed in molarity (M), defined as the number of moles of solute per liter of solution.

• A common unit of concentration in chemistry is molarity (M), which is moles per liter of solution.

Preparation of Sodium Chloride Solution

• The target solution is a 0.25 molar sodium chloride solution, with a total volume of 500 mL.

• Calculation of sodium chloride required:

  • 0.25 moles/L x 0.5 L = 0.125 moles.

  • Total mass needed: 0.125 moles x 58.44 g/mole = 7.34 g.

Measuring the Solute

• Use a clean lab scoop and balance to measure 7.34 g of sodium chloride accurately.

• Do not return excess reagent to the original container; use a separate container instead.

Using Volumetric Flasks

• Transfer the measured sodium chloride to a volumetric flask for improved accuracy.

• Add water to dissolve the solute, filling to about half of the flask initially.

• Once dissolved, carefully add water to reach the 500 mL mark, monitoring the meniscus.

Final Concentration Calculation

• Calculate the concentration after preparing the solution:

  • Measured mass (7.34 g) divided by molar mass (58.44 g/mole) gives moles.

  • Divide the number of moles by the volume (0.5 L) for the final concentration.

• The resulting concentration is approximately 0.251 M.

Labeling and Storage

• Clearly label the storage container with the contents and concentration for safety.

• The demonstration provides a practical application for preparing solutions in laboratory settings.