Defining a Stock Solution
A stock solution is a concentrated solution that is prepared in a precise concentration and stored for later use. It serves as a standard from which more dilute solutions, known as working solutions, can be easily and accurately prepared through a process called dilution.
Section 2: Purpose and Advantages
The primary purpose of a stock solution is to improve efficiency and accuracy in the lab. Instead of repeatedly weighing out small, difficult-to-measure amounts of a solid solute, a scientist can prepare one large, accurately measured concentrated solution and then dilute small portions of it as needed. This saves time, reduces waste, and minimizes measurement errors.
Section 3: A Practical Example
Imagine you need to prepare several 100 mL solutions of 0.1 M sodium chloride (NaCl). Instead of weighing out 0.5844 g of NaCl each time, you could prepare a 1 L stock solution of 1.0 M NaCl by dissolving 58.44 g of NaCl in 1 L of water. To make a 100 mL working solution of 0.1 M, you would simply take 10 mL of the stock solution and dilute it with water to a final volume of 100 mL.
Section 4: Preparation and Calculation
Preparing a stock solution requires careful measurement of the solute and the solvent. The calculation for making dilutions from a stock solution is based on the dilution formula: M1V1 = M2V2, where M1 is the concentration of the stock solution, V1 is the volume of the stock solution needed, M2 is the desired concentration of the final solution, and V2 is the final volume of the diluted solution.