What mass of sodium chloride and what mass of water are needed to prepare 800 g of 20% NaCl solution?

Given:

W = 20%

m (solution) = 800 g,

m (water) – ?.

m (substances) -?

Decision :

The mass fraction of a substance is calculated by the formula:

W = m (substance): m (solution) × 100%,

m (substance) = (m (solution) × W): 100%,

m (substance) = (800 g × 20%): 100% = 160 g.

m (solution) = m (substance) + m (water).

m (water) = m (solution) – m (substance)

m (water) = 800 g – 160 g = 640 g.

Answer: to prepare 800 g of a 20% solution, you need to take 160 g of salt and add 640 g of water.