How To Prepare Solutions

Summary

The video explains how to prepare a solution of a specified concentration from a solid. The amount of solid needed is calculated using molarity, which is the number of moles of solute per liter of final solution.

Method for Preparing a Solution

1. Identify the required molarity and final volume.
2. Convert the volume to liters.
3. Check the chemical formula and label to determine whether the solid is anhydrous or hydrated, as this affects its molar mass.
4. Calculate the required mass:
   • Use molarity = moles ÷ liters to find the required moles.
   • Multiply the moles by the substance’s molar mass to find the mass of solid.
5. Weigh the calculated amount using a balance.
6. Prepare the solution in a volumetric flask:
   • Add some water to the flask.
   • Add the solid and stir until it dissolves.
   • Add more water while mixing until the solution reaches the required final volume.

Example

To prepare 500 mL of 0.5 M copper(II) chloride solution, the video uses copper(II) chloride dihydrate, which has a formula mass of about 170.49 g/mol. The calculation gives 42.62 g of solid.

The video also notes that Flinn Scientific’s catalog and reference manual provide additional solution recipes and preparation guidance.

Speaker and Source

• Narrator: An instructional voice; no individual speaker is named in the subtitles.
• Source: Flinn Scientific instructional demonstration.