Final answer:
Indicators used to determine the pH of an unknown acid include litmus paper, pH meter, and bromothymol blue among others, each showing distinct color changes at specific pH intervals.
Step-by-step explanation:
The indicators that could be used to determine the pH of an unknown acid include litmus paper, which changes color from pink to blue as the solution goes from acid to base; a pH meter, which measures the pH value electronically; and bromothymol blue, which has a yellow color below a pH of about 3 and a blue-violet color above a pH of about 4. Other indicators like methyl orange, universal indicator, phenolphthalein, red cabbage juice, and Congo red also exhibit color changes at specific pH levels and could be used depending on the pH range of interest.
Indicators such as phenolphthalein and universal indicator can provide a visual representation of pH levels through distinct color changes. Phenolphthalein, for example, is colorless in acidic solutions and turns pink in basic solutions (with optimal color change at pH 8.3 and above), while universal indicators display a range of colors across the pH spectrum, allowing for an estimation of the pH value.