Question

What is a standard solution? Describe the steps involved in preparing a standard solution.

Short answer

A standard solution is a solution with a known concentration used for calibration, titration, or other analytical procedures requiring accuracy and precision. To prepare a standard solution, follow these steps: 1) Choose an appropriate compound with high purity and known molecular weight. 2) Weigh the desired mass of the compound accurately using an analytical balance. 3) Dissolve the compound in a suitable solvent like distilled water. 4) Transfer the dissolved compound to a calibrated volumetric flask, using a funnel and rinsing the container with solvent. 5) Dilute the solution to the calibration mark on the volumetric flask with more solvent. 6) Mix the solution thoroughly by inverting the volumetric flask. 7) Label and store the standard solution properly to avoid changes in concentration.

Step-by-step solution

1. Understanding a Standard Solution

A standard solution is a solution of known concentration that is used for calibration, titration, or other analytical procedures in which accurate and precise concentrations are required. Standard solutions are commonly used in quantitative analyses in chemistry to determine the concentration of an unknown substance in a sample.

2. Choosing the Appropriate Compound

First, choose a suitable compound to be used as the standard solution. This compound should have desirable characteristics such as high purity, stability, minimal hygroscopicity (absorption of moisture from the air), and an accurately known molecular weight.

3. Weighing the Compound

Carefully weigh the desired mass of the chosen compound using an analytical balance. The mass should be calculated based on the desired concentration of the standard solution and the volume that will be prepared. Record the precise mass of the compound used.

4. Dissolving in Solvent

Dissolve the weighed compound in a portion of the solvent. Choose a solvent that will dissolve the compound well and is compatible with the analytical procedure where the standard solution will be used. Typically, solvents like distilled water or other aqueous solutions are used.

5. Transfer to Volumetric Flask

Transfer the dissolved compound to a calibrated volumetric flask. Use a funnel to avoid spillage and loss of compound. Rinse the container used to dissolve the compound with the solvent and pour the rinse into the volumetric flask to ensure that all traces of the compound are transferred.

6. Dilution to the Mark

Dilute the solution to the calibration mark on the neck of the volumetric flask by adding solvent. The volume of the standard solution should now be precisely known, and the solution is homogeneous. In most cases, mix the solution by inverting the closed volumetric flask multiple times to ensure thorough mixing and an accurate concentration.

7. Labeling and Storage

Label the volumetric flask with the name and concentration of the compound, the date of preparation, and any other relevant information. Store the standard solution in an appropriate container like a glass bottle with a tightly sealed stopper to avoid contamination, evaporation, or other changes in concentration. By following these steps, a standard solution with a known concentration can be prepared and utilized in analytical chemistry for accurate quantitative analyses.