Final answer:
To determine the number of grams of NaCl in 20.0 mL of a 1.20% (w/v) NaCl solution, you multiply the volume of the solution by the percent concentration divided by 100, resulting in 0.24 grams of NaCl.
Step-by-step explanation:
To calculate the number of grams of NaCl in 20.0 mL of a 1.20% (w/v) NaCl solution, you need to know the definition of percent concentration by mass/volume (% m/v). Percent concentration means you have that percentage of the solute's mass for each 100 mL of the total solution. In this case, a 1.20% (w/v) NaCl solution means there are 1.20 grams of NaCl in every 100 mL of the solution.
To find the mass of NaCl in 20.0 mL of solution, use the proportion:
Mass of NaCl = 1.20 g/100 mL * 20.0 mL
So,
Mass of NaCl = (1.20 g/100 mL) * (20.0 mL)
= 0.24 g
Therefore, there are 0.24 grams of NaCl in 20.0 mL of the solution.