Experiment Overview

Solution preparation and standardization are essential laboratory techniques used to prepare solutions of known concentration and accurately determine their exact molarity. Standardization is especially important for solutions that cannot be prepared accurately by direct weighing alone.

What This Experiment Demonstrates

• Preparation of standard solutions using volumetric techniques
• Accurate measurement of mass and volume
• Determination of exact concentration through titration

Apparatus Required

• Analytical balance
• Volumetric flask
• Burette
• Pipette
• Conical flask
• Beaker
• Funnel
• Wash bottle
• Glass rod

Chemicals Required

• Primary standard substance (e.g. sodium carbonate or oxalic acid)
• Solution to be standardized (e.g. \(\ce{NaOH}\) or \(\ce{HCl}\))
• Suitable indicator
• Distilled water

Theory

A standard solution is a solution whose concentration is known accurately. It can be prepared either by direct weighing of a pure substance or by standardization against a primary standard.

A primary standard is a highly pure, stable, non-hygroscopic substance with a known formula mass. It is used to determine the exact concentration of another solution.

During solution preparation, a calculated mass of solute is dissolved in distilled water and diluted to a fixed volume in a volumetric flask.

\[M = \frac{n}{V}\]

where \(M\) is molarity, \(n\) is the number of moles of solute, and \(V\) is the volume of solution in liters.

Some solutions, such as sodium hydroxide, absorb moisture or carbon dioxide from air, making their concentration inaccurate if prepared directly. These solutions must therefore be standardized using titration.

In standardization, the unknown solution reacts with a primary standard solution of known concentration. Using stoichiometry and titration data, the exact concentration of the unknown solution can be calculated.

Method

1. Accurately weigh the required mass of the solute using an analytical balance.
2. Dissolve the solute in a small volume of distilled water in a beaker.
3. Transfer the solution into a volumetric flask using a funnel.
4. Rinse the beaker and funnel with distilled water and add the washings to the flask.
5. Add distilled water up to the calibration mark of the volumetric flask.
6. Stopper and invert the flask several times to mix thoroughly.
7. Pipette a measured volume of the primary standard solution into a conical flask.
8. Add a suitable indicator.
9. Titrate using the solution being standardized until the endpoint is reached.
10. Repeat the titration to obtain concordant results.

Observations

The prepared solution should appear homogeneous and free from undissolved particles. During standardization, a clear indicator color change is observed at the endpoint.

Calculations

• Calculate moles of solute used in preparing the standard solution.
• Determine the molarity using:

\[M = \frac{n}{V}\]

• Use titration stoichiometry to calculate the exact concentration of the unknown solution.

Result

A solution of accurately known concentration is successfully prepared and standardized using volumetric analysis techniques.

Video Demonstration

Video courtesy of Carolina Science (YouTube). Video used for educational purposes under YouTube’s embedding policy.