Question

2. Describe in detail how to prepare 100.0 milliliters of a 5.0 x 10-5 M NaCl solution starting from a 2.0 x 10-4 M NaCl stock solution. Be mindful of the glassware available in the lab. Explicitly state and describe in detail ALL steps necessary to make the solution, including which pieces of glassware you would need to use. (more than just calculations)!

Answer 1

Answer and Explanation:

We have the following volumes and concentrations:

Ci = 2.0 x 10⁻⁴ M (initial concentration)

Cf= 5.0 x 10⁻⁵ M (final concentration)

Vf= 100.0 ml (final volume)

We have to first calculate the volume we have to take (Vi) of stock solution. For this, we use the following equation:

Ci x Vi = Cf x Vf

⇒ Vi = (Cf x Vf)/Ci = (5.0 x 10⁻⁵ M x 100.0 ml)/2.0 x 10⁻⁴ M = 25.0 ml

Thus, we have to take 25 ml of the 2.0 x 10⁻⁴ M solution and then we have to add water until reaching a total volume of 100.0 ml.

We need a volumetric flask of 100 ml. We take 25.0 ml of 2.0 x 10⁻⁴ M NaCl solution (by using a measuring cylinder of 30 ml or 50 ml), transfer the 25.0 ml to the volumetric flask and finally we add water until fulfill the flask capacity. Finally, we have to homogenize the solution in the flask.