How many grams of sodium chloride do you need to prepare 250 mL of a 5.00% (w/v) sodium chloride solution?

To determine the number of grams of sodium chloride needed to prepare a 5.00% (w/v) sodium chloride solution, we'll need to use the weight/volume percent formula:

(weight of solute in grams / volume of solution in mL) x 100 = weight/volume percent

In this case, we are given the volume of the solution (250 mL) and the weight/volume percent (5.00%). We need to find the weight of sodium chloride.

Let's break down the steps to find the answer:

Step 1: Convert the weight/volume percent to a decimal.
5.00% = 5.00/100 = 0.05

Step 2: Calculate the weight of sodium chloride.
(weight of solute in grams / 250 mL) x 100 = 0.05

Rearranging the formula:
weight of solute in grams = (0.05 x 250 mL) / 100

Simplifying the equation:
weight of solute in grams = 0.125 g

Therefore, you will need 0.125 grams of sodium chloride to prepare 250 mL of a 5.00% (w/v) sodium chloride solution.