Question

distinguishing mixtures from pure substances through physical properties
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 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 continues to rise as the powder slowly melts, and the last of the powder becomes liquid at 76.0 °c.
sample b is a solid yellow cube with a total mass of 50.0 g. the cube is divided into two smaller 25.0 g subsamples, and the minimum volume of water needed to dissolve each subsample is measured. the first subsample just barely dissolved in 101 ml of water, the second in 92 ml. when the experiment is repeated with a new 50.0 g sample, the minimum volume of water required to dissolve the two subsamples is 89 ml and 93 ml.
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.\ pure substance
mixture
(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.\ pure substance
mixture
(cant decide)

Explanation:

Step1: Analyze sample A's melting - point

Pure substances have a sharp melting - point. Sample A melts over a range of temperatures ($66.2^{\circ}C$ to $76.0^{\circ}C$), which is characteristic of a mixture.

Step2: Analyze sample B's solubility

For a pure substance, the solubility in a given solvent under the same conditions should be consistent. The solubility of sample B in water varies for different subsamples and different trials, indicating it is a mixture.

Answer:

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