Question

Read the descriptions below of two substances and an experiment on each. Decide whether the result of the experiment tells you the substance is a pure substance or a mixture, if you can.

• Sample A is a solid yellow cube with a total mass of 50.0 g. The cube is ground to a fine orange powder and added to a 500 ml beaker full of water. The beaker is stirred vigorously. Some of orange powder settles to the bottom of the beaker, and some rises to the top and floats on the water. When the powder at both the bottom and the top of the beaker is filtered out, dried, and weighed, the total mass is measured to be 50.1 g.

• Sample B is 100 mL of a clear liquid. The density of the liquid is measured, and turns out to be 0.77 g/mL. The liquid is then heated in a flask until it boils. The vapor that rises off the bolling liquid is collected for 10 minutes and cooled until it condenses into a separate beaker. The density of the liquid that remains in the flask is then measured, and turns out to be 1.04 g/mL.

Required:
Is sample A made from a pure substance or a mixture?

Answer 1

Sample A is a mixture

Sample B is a mixture

Step-by-step explanation:

If we look at sample A, we can easily notice that the sample powder was found to float while some of it settled below. This means that the sample is not entirely homogeneous. A homogeneous sample always constitutes a single phase in solution. Also, the dried mass yields 50.1 g while only 50.0 g of the yellow cube was ground and dissolved. This shows that the original cube is not pure. A sample that is not entirely homogeneous is not pure.

Secondly, the fact that the density of liquid that remains in the flask is different from the density of the sample initially measured indicates that the original sample B is a mixture of substances.