Answer:
5% (w/v), by definition, means 5 grams of solute per 100 grams of solution. Since the density is 1.2 g/ml, you can find the volume of 100 grams of solution. 100 g solution x 1 ml/1.2 g = 83.33 mls. Hence...
83.33 mls x 5 g/100 mls = 4.17 g solute needed.
