Question

pure substance or mixture results
substance | description | sample gently heated in a test tube | sample put in freezer overnight
1 | small brown, odorless crystals | crystals turn black. | no visible change
2 | small white, odorless crystals | crystals turn brown, then black. | no visible change
3 | clear colorless, odorless liquid | liquid bubbles and then evaporates. | liquid turns into a solid.
4 | clear blue, odorless liquid | liquid bubbles and then evaporates and small blue crystals are left behind. | liquid remains a liquid.
which statement identifies the mixture and provides evidence that best supports the claim?
a substance 1 is a mixture because the crystals turn black when heated.
b substance 2 is a mixture because the crystals turn different colors when heated.
c substance 3 is a mixture because the liquid bubbles and then evaporates when heated.
d substance 4 is a mixture because the liquid evaporates and leaves small blue crystals behind.

Explanation:

To determine the mixture, we analyze each option:

• Option A: Color change on heating doesn't necessarily indicate a mixture (pure substances can decompose/change color).
• Option B: Similar to A, color change alone isn't proof of a mixture.
• Option C: Bubbling and evaporation could be a physical change (like water boiling), not proof of a mixture.
• Option D: When Substance 4 is heated, the liquid evaporates and leaves blue crystals behind. This shows different components (liquid and solid crystals) separating, a key characteristic of a mixture.

Answer:

D. Substance 4 is a mixture because the liquid evaporates and leaves small blue crystals behind.