Question

a teacher challenged a group of students to identify an unknown white solid. the students recorded the following results in their investigation.

\

$$\begin{tabular}{|c|l|l|} \\hline test & test type & results \\\\ \\hline a & density & \\(2.13\\text{ g/cm}^3\\) \\\\ \\hline b & melting point & \\(140\\text{ }^{\\circ}\\text{c}\\) \\\\ \\hline c & microscope & crystalline structure observed \\\\ \\hline d & mixed with \\(\\text{hclo}_4\\text{(aq)}\\) & heat generated \\\\ \\hline \\end{tabular}$$

question 12
which of the tests listed provides evidence of a chemical property of the unknown solid?

test a
test b
test c
test d

Explanation:

Define physical and chemical properties

Physical properties can be observed or measured without changing the chemical identity of the substance. Chemical properties describe how a substance undergoes a chemical reaction to form new substances.

Analyze Test A, B, and C

Test A (Density), Test B (Melting point), and Test C (Microscope observation of crystalline structure) measure characteristics that do not alter the chemical composition of the solid. These are physical properties.

Analyze Test D

Test D involves mixing the solid with perchloric acid \(\text{HClO}_4\text{(aq)}\). The generation of heat indicates a chemical reaction occurred, which demonstrates a chemical property of the substance.

Connect to experimental design

Using Experimental Design, we identify which test measures a chemical change. Test D provides direct evidence of a chemical property.

Answer:

• Test A
• Test B
• Test C
• Test D (Correct answer)