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 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 cooled in the refrigerator. at 10.0 °c crystals begin to appear until the liquid is about half crystal, half liquid. after 30 minutes, no more crystals appear, even though the temperature is lowered to 6.3 °c.

sample b is 100 g of a coarse grey powder with a faint unpleasant smell. 15 mg of the powder are put into a very thin tube and heated. the powder begins melting at 66.2 °c. the temperature stays constant as the powder slowly melts. after the last of the powder melts, the temperature starts to rise again, eventually reaching 76.0 °c.

is sample a made from a pure substance or a mixture?
if the description of the substance and the outcome of the experiment isnt enough to decide, choose \cant decide.\

is sample b made from a pure substance or a mixture?
if the description of the substance and the outcome of the experiment isnt enough to decide, choose \cant decide.\

Explanation:

Step1: Analyze sample A

A pure substance has a sharp melting - freezing point. Sample A starts to form crystals at 10.0 °C and then stops forming crystals at 6.3 °C while cooling, which indicates a non - sharp freezing point. This is characteristic of a mixture.

Step2: Analyze sample B

A pure substance has a constant melting point. Sample B melts at a constant temperature of 66.2 °C until all of it is melted, which is characteristic of a pure substance.

Answer:

Is sample A made from a pure substance or a mixture?
mixture
Is sample B made from a pure substance or a mixture?
pure substance