Question

In a lab there are two different samples, which are the following Sample A is 100.g of a coarse grey powder with a faint unpleasant smell. 15.g of the powder are dissolved in ethanol. 0.5mg of the resulting black solution is carefully dropped onto a thick sheet of paper laid flat in a tray. After 30 minutes the initial round black stain has spread out and faded in color to a deep purple. Additionally, there is a dark green ring surrounding the inner stain. Sample B is a solid yellow cube with a total mass of 50.0g. The cube is divided into two smaller 25.0g 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 50.0g. sample, the minimum volume of water required to dissolve the two subsamples is 89.mL and 93.mL. Determine whether each is a mixture, pure substance, or can't decide.

Answer 1

Sample A is likely a mixture because of the varied properties it showed when dissolved in ethanol. Sample B is likely a pure substance based on its consistent behavior when it was dissolved in water.

Step-by-step explanation:

Based on the provided information, Sample A exhibits the characteristics of a mixture. This is supported by the occurrences when it's subjected to certain processes, such as dissolving in ethanol and subsequent changes in color (from black to deep purple and then a green ring around the stain).

Mixtures often show varied properties throughout different parts as their components do not combine chemically.

Sample B can be considered a pure substance. This is evident from its consistent behavior when dissolved in water, and the small divergence in the volume of water required to dissolve equal masses can be attributed to experimental errors.

Pure substances show consistent properties because they have the same composition throughout.

Learn more about Differentiating Mixtures and Pure Substances