How to Prepare a 0.2 M Sodium Chloride (NaCl) Solution: Step-by-Step Guide and Calculations

Preparing a 0.2 M sodium chloride (NaCl) solution is a common task in many laboratory settings. This article provides a detailed step-by-step guide, along with necessary calculations, to help you prepare this solution accurately.

Understanding the Components

To prepare a 0.2 M NaCl solution, you need to identify the solute (sodium chloride, NaCl) and the solvent (water) as well as the appropriate laboratory glassware (volumetric flask).

Step-by-Step Procedure

1. **Calculate the Mass of NaCl Needed**

The first step is to calculate the amount of NaCl required to achieve a 0.2 M concentration in 1 liter of solution. The formula for calculating the mass of solute is:

Molarity (M) Moles of Solute / Liters of Solution

For a 0.2 M solution:

0.2 M Moles of NaCl / 1 L

Therefore, Moles of NaCl 0.2 mol/L × 1 L 0.2 mol

The molar mass of NaCl is 58.44 g/mol. So, the mass of NaCl required can be calculated as:

Mass of NaCl Moles × Molar Mass 0.2 mol × 58.44 g/mol 11.688 grams

Weigh the NaCl

Using a digital balance, accurately measure 11.688 grams of NaCl and transfer it to the volumetric flask.

Add Water

Start by adding distilled water to the volumetric flask, filling it to about the neck of the flask. Do not fill it to the very top as you’ll need to add a little more water after mixing.

Mix the Solution

Stopper the volumetric flask and invert it several times to ensure that the NaCl is completely dissolved.

Adjust the Volume

Add distilled water dropwise until the meniscus (the curved surface of the liquid) is exactly at the calibration mark on the volumetric flask. Stopper the flask and invert it a few more times to ensure the solution is thoroughly mixed.

Label the Solution

After preparing the solution, label the flask with the concentration (0.2 M), the solute (NaCl), and the date of preparation.

Your 0.2 M NaCl solution is now ready.

Necessary Calculations for Different Volumes

The steps above provide a general guide for preparing a 0.2 M NaCl solution in 1 liter. However, you can adjust the volume of the solution using similar calculations.

Step 1: Calculate the Molecular Weight of NaCl

The molecular weight of NaCl can be calculated as follows:

Molecular weight of NaCl (22.99 g/mol for Na) (35.45 g/mol for Cl) 58.44 g/mol

Step 2: Determine the Amount of NaCl Needed

To find out how many grams of NaCl are needed to make a 0.2 M solution, use the formula:

mass (g) Molarity (M) × Molecular weight (g/mol) × Volume (L)

Example Calculation:

Let’s say you want to prepare 1 liter (1 L) of a 0.2 M NaCl solution:

Molarity (M) 0.2 M

Volume (L) 1 L

Molecular Weight of NaCl 58.44 g/mol

Now plug the values into the formula:

mass (g) 0.2 mol/L × 58.44 g/mol × 1 L 11.688 g

Therefore, you need 11.688 grams of NaCl to prepare 1 liter of a 0.2 M NaCl solution.

Step 3: Prepare the Solution

Accurately weigh out the calculated amount of NaCl. Dissolve the NaCl in a small amount of distilled water in a beaker or flask. Transfer the solution to a 1 L volumetric flask. Add distilled water until the total volume reaches 1 L, ensuring the NaCl is fully dissolved.

Adjusting for Different Volumes

For example, if you want to make 500 mL (0.5 L) of a 0.2 M solution, you can adjust the calculation as follows:

mass (g) 0.2 mol/L × 58.44 g/mol × 0.5 L 5.844 g

Therefore, you would weigh out 5.844 grams of NaCl for 500 mL of a 0.2 M solution.

This article provides a comprehensive guide to preparing 0.2 M NaCl solutions in different volumes, ensuring accuracy and consistency in your laboratory procedures.