Question

Describe the steps involved in preparing a solution of known molar concentration using a volumetric flask.

Short answer

To prepare a solution of known molar concentration, first understand the concept of molarity. Calculate and measure the amount of solute needed using molarity formula. Add the solute to the volumetric flask using a funnel. Then add the solvent to the flask until it almost reaches the final volume mark, mix then add more solvent until it reaches the mark. Mix the solution thoroughly to ensure full dissolution of solute.

Step-by-step solution

Understanding Molarity

Molarity (M) is a measure of the concentration of a solute in a solution, or of any chemical species, in terms of amount of substance in a given volume. It is defined as the amount of moles of solute dissolved per litre of solution. The equation for molarity is: \( M = \frac{n}{V} \) where \( M \) is the molarity, \( n \) is the number of moles of solute, and \( V \) is the volume of the solution in litres.

Measuring the Solute

First, the quantity of solute needed should be calculated based on the desired molarity and volume. This can be done using the molarity formula. For example, to prepare 1L of 1M solution of Sodium Chloride (NaCl), one would need to measure out 1 mole of NaCl because \( 1M = \frac{1\, mole}{1\, Litre} \).

Adding the Solute to the Flask

After weighing the right amount of solute, add it into a clean, dry volumetric flask. This is typically done using a funnel to prevent any loss of solute.

Adding The Solvent to The Flask

Next, add solvent to the flask containing the solute. It's important to add the solvent in increments, especially when close to the mark on the flask indicating the final volume. The solvent is most commonly water.

Making Up The Volume and Mixing

Finally, add enough solvent to reach the mark on the neck of the flask which corresponds to the desired final volume (for example, the 1L mark). This is performed under careful inspection at eye level. After reaching the mark, secure the stopper on the flask and invert it several times to thoroughly mix the solution, ensuring that all the solute has been fully dissolved.