Preparing Solutions: Practical Examples & Tips

Learn how to prepare solutions of specific concentrations with real-world examples.
By Jamie

Understanding Concentration and Dilution Calculations

In chemistry, preparing solutions of specific concentrations is a fundamental skill. Concentration refers to the amount of solute present in a given volume of solvent or solution. Dilutions are often necessary to achieve the desired concentration for experiments, analyses, or industrial applications. Here are three practical examples that illustrate how to prepare solutions of specific concentrations.

Example 1: Preparing a 0.5 M Sodium Chloride Solution

In a laboratory setting, a biochemist may need to prepare a sodium chloride (NaCl) solution for an experiment involving cell osmotic pressure. A 0.5 M solution is required for this experiment.

To prepare this solution, we need to calculate the amount of NaCl needed:

  • Molar mass of NaCl: 58.44 g/mol
  • Desired concentration: 0.5 moles/L (0.5 M)
  • Volume of solution required: 1 L

Using the formula:
Amount of solute (grams) = Molarity (mol/L) × Molar mass (g/mol) × Volume (L)
Amount of NaCl = 0.5 mol/L × 58.44 g/mol × 1 L = 29.22 g

To prepare the solution:

  1. Weigh 29.22 grams of NaCl using an analytical balance.
  2. Add the NaCl to a volumetric flask.
  3. Add distilled water gradually until the total volume reaches 1 liter.
  4. Mix thoroughly to ensure complete dissolution.

Notes: If you need to prepare a smaller volume, simply adjust the calculations accordingly. For example, for 500 mL, you would use 14.61 g of NaCl.

Example 2: Creating a 10% (w/v) Glucose Solution

In a clinical setting, nurses often prepare glucose solutions for patients requiring intravenous therapy. A 10% (w/v) glucose solution is commonly used.

In this case, the preparation involves:

  • Desired concentration: 10% (w/v) means 10 grams of glucose per 100 mL of solution.
  • Volume of solution required: 500 mL

To prepare the solution:

  1. Calculate the total amount of glucose needed:
    Total glucose = (10 g/100 mL) × 500 mL = 50 g
  2. Weigh out 50 grams of glucose.
  3. Add the glucose to a 500 mL volumetric flask.
  4. Add distilled water until the total volume reaches 500 mL.
  5. Mix the solution well.

Notes: This method can be adjusted for any volume. For example, to prepare 250 mL, you would need 25 g of glucose.

Example 3: Making a 1:10 Dilution of an Acid Solution

In an industrial laboratory, technicians may need to dilute a concentrated hydrochloric acid (HCl) solution for safe handling. A 1:10 dilution is required for routine cleaning purposes.

The preparation involves:

  • Concentration of the stock solution: 37% HCl
  • Desired dilution: 1 part HCl to 10 parts water (1:10)
  • Volume of diluted solution required: 1 L (1000 mL)

To prepare the dilution:

  1. Using the dilution factor, calculate the amount of concentrated HCl needed:
    Volume of HCl = Total volume / (Dilution factor + 1)
    Volume of HCl = 1000 mL / (10 + 1) = 90.91 mL
  2. Measure 90.91 mL of concentrated HCl using a graduated cylinder.
  3. Carefully add this to a 1 L volumetric flask.
  4. Add distilled water to reach the 1 L mark.
  5. Mix thoroughly.

Notes: Always add acid to water, never the other way around, to prevent exothermic reactions that can cause splattering. For smaller or larger volumes, adjust the stock volume accordingly (e.g., for 500 mL, use 45.45 mL of HCl).

These examples highlight the practical application of preparing solutions of specific concentrations, demonstrating the importance of accurate measurements and calculations in various fields.