Question

Kia is doing an experiment in science lab. She is given a beaker containing 100 g of liquid. The beaker has markings on the side for measuring volume. The water comes up to the 100 mL mark. Kia puts the liquid on a hot plate by mistake. By the time she realizes the mistake, half of her liquid has evaporated.
Kia still needs 100 g of liquid for her experiment. To find out how much liquid she has to replace, she needs to re-weigh her liquid. However, the balance she used before is now broken. The teacher tells Kia that she can tell how much water is left by looking. The water now comes up to the 50 mL mark.

How much mass does Kia's remaining water have?

Answer 1

The correct answer is 50g.

Answer 2

The key to solving this problem is density. Density determines the mass of a molecule for a certain volume. Kia is given a beaker containing 100 g which volume is at 100 mL mark. Then the density of the liquid would be:
density=mass/volume
density= 100g/ 100ml= 1g/ml

If the water now comes up to the 50 mL mark, then the weight would be:
density = mass/volume
mass = volume * density
mass = 50ml * (1g/ml)= 50g