Final answer:
The student uses litmus paper tests, solubility, and conductivity to classify unknown compounds. Acids turn blue litmus paper red, bases turn red litmus paper blue, and salts are conductive in solution. By these criteria, the unknown compounds are matched with their corresponding chemical formulas.
Step-by-step explanation:
The student's task is to use experimental results to match each unknown compound with its chemical formula. The results from the litmus paper tests, solubility, and conductivity provide clues about the chemical nature of these compounds. Acids will turn blue litmus paper red and do not change the color of red litmus paper. On the other hand, bases will turn red litmus paper blue and do not change the color of blue litmus paper. Conductivity experiments can also help classify compounds as electrolytes (which conduct electricity) or nonelectrolytes (which do not conduct electricity).
Compounds that change blue litmus paper to red are acids, like HCl. Those that change red litmus paper to blue are bases, like Ca(OH)2. A soluble and conductive liquid that does not change the color of red litmus paper is likely to be a neutral salt, which dissolves to give ions, making it conductive. Using these observations, the student can make educated predictions regarding the identities of the unknown compounds.
Unknown Compound 1 does not conduct electricity and does not change red litmus paper, indicating it is a weak electrolyte or nonelectrolyte and is not an acid or a base (such as an organic compound like CH4). Unknown Compound 2 conducts electricity and does not affect red litmus, suggesting it is a salt. Unknown Compound 3 turns the blue litmus red, identifying it as an acid (HCl). And Unknown Compound 4, which turns red litmus blue, is a base (Ca(OH)2).