Question

mark decided to investigate some household materials using the phenolphthalein solution. he placed 10 drops of each liquid or a small amount of solid (just enough to cover the tip of the spatula) in 2 ml of distilled water. then he added 2 drops of the phenolphthalein solution and identified each substance as either an acid or a base, as shown in the table:

a. can you draw any general conclusions about household materials based on his results?
b. can you find any problems with marks logic? explain.

Explanation:

a. From the table, we can see that some household materials are acids (white vinegar, salt, apple juice, milk) and some are bases (baking soda, shampoo, window cleaner). So a general conclusion is that household materials can be either acidic or basic.
b. Phenolphthalein is a common indicator. It is colorless in acidic solutions and turns pink in basic solutions (above pH 8.2). However, for substances like salt (\(NaCl\)), it is a neutral salt. But Mark classified it as an acid. The error is that he assumed any substance that does not turn phenolphthalein pink is an acid. In reality, neutral substances (like a neutral salt solution) will also not turn phenolphthalein pink. Also, for substances like shampoo and window - cleaner, just because the color changes (in the case of window - cleaner) or remains (in the case of shampoo, assuming the initial color was due to other non - pH - related factors like additives) does not necessarily mean they are bases. There could be other substances in the shampoo or window - cleaner that affect the color change (or lack thereof) other than the pH (e.g., surfactants in shampoo that might interact with the indicator in a non - pH - related way).

Answer:

a. Household materials can be either acidic or basic.
b. Mark's logic has problems. For example, he classified salt (\(NaCl\)) as an acid. Salt is a neutral salt, and phenolphthalein is colorless in neutral solutions too. Also, for substances like shampoo and window - cleaner, there could be other non - pH - related factors (like additives in the products) that affect the color change (or lack thereof) with phenolphthalein, not just the acidity or basicity.