Question

Simon has collected three samples from the coral reef where he observes marine life. He must determine whether each one is a pure substance or a mixture.
SAMPLE A : Clear liquid. Evaporates at 70*C. Appearance does not change.
SAMPLE B : Clear, blue liquid. Boils at 90*C leaving blue crystals behind. Appearance does not change.
SAMPLE C : Opaque, whitish liquid. Boils at 100*C leaving white crystals behind. Dust appears to settle at bottom.

Answer choices for each one are - homogeneous mixture, heterogeneous mixture, or pure substance

Answer 1

SAMPLE A - pure substance.
SAMPLE B - homogeneous mixture.
SAMPLE C - heterogeneous mixture.
Pure substance - constant composition and properties.
Homogeneous mixture - same uniform appearance and composition.
Heterogeneous mixture - not uniform in composition, two phases (liquid and dust).

Answer 2

Answer: Sample A is a pure substance, Sample B  is a homogeneous mixture and Sample C is a heterogeneous mixture.

Explanation:

Homogeneous mixture : In these mixture, all the component are uniformly distributed throughout the mixture.For example: sugar-water solution.

Heterogeneous mixture : In these mixture, all the component are not uniformly distributed throughout the mixture.For example: sand-water solution.

Pure substance : These are the substance made up only one type of atom or molecule.They have fixed value of boiling and melting points. For example: diamond, pure sugar etc.

Sample A is a clear liquid which evaporates at $70^oC$ with no change in appearance. Hence, pure substance.

Sample B is a clear blue liquid which boils at $90^oC$ and leaves blue crystals behind with change in appearance. Hence, homogeneous mixture

Sample C is a opaque, whitish liquid which boils at $100^oC$ and leaves white crystals behind with dust particles settled in the bottom. Hence, heterogeneous mixture.