What is the mass of dry NaCl sample should be taken for 100 cm3 of 0.5 mol/dm3 aqueous solution?

To determine the mass of a dry NaCl sample needed for a given volume and concentration of an aqueous solution, you need to use the equation:

Concentration (mol/dm³) = Moles of solute / Volume of solution (dm³)

In this case, you have a concentration of 0.5 mol/dm³ and a volume of 100 cm³ (which is equal to 0.1 dm³). Let's calculate the moles of NaCl needed:

Moles of NaCl = Concentration × Volume

Moles of NaCl = 0.5 mol/dm³ × 0.1 dm³

Moles of NaCl = 0.05 moles

Now, to determine the mass of the NaCl sample, you need to use the equation:

Mass = Moles × Molar mass

The molar mass of NaCl is 58.44 g/mol. Let's calculate the mass:

Mass = 0.05 moles × 58.44 g/mol

Mass = 2.922 g

Therefore, a dry NaCl sample with a mass of approximately 2.922 grams should be taken for 100 cm³ of a 0.5 mol/dm³ aqueous solution.