Final answer:
A student can determine whether an unknown chemical is an acid by performing an acid-base titration, which tests the hydrogen ion concentration in the sample until the indicator shows neutrality.
Step-by-step explanation:
To determine whether an unknown chemical is an acid, a student could test the hydrogen ion concentration in the sample. This can be done by performing an acid-base titration, which involves adding a solution with a known concentration to the unknown solution until neutrality is achieved, indicated by a pH meter or a color change in a pH indicator. In a titration, after adding an indicator, such as phenolphthalein, to the unknown acid, a known concentration of a base, like NaOH, is added gradually until the indicator changes color, signaling that the reaction has reached neutrality. By knowing the volume and concentration of the base added, one can calculate the moles of H+ ions initially present in the acid solution. This process effectively measures the hydrogen ion concentration, reflecting the substance's acidity.