Red cabbage contains a water-soluble pigment. In a highly acidic solution, the pigment turns bright red, and in a moderately acidic solution, it turns pinkish. In a highly basic solution, the pigment turns yellow, and in a moderately basic solution, it turns bluish.

Question

A student makes a pH indicator from red cabbage that has a reddish-purple color with a pH of approximately 7. The student pours the same amount of the cabbage solution into each of four different beakers. He then adds a different household solution to each of the four beakers until a color change is obtained. His results are shown in the table below.
The student finds the following chart online from someone else’s cabbage pH indicator investigation.
Based on the information in the passage, which household solution has the highest pH?

a
club soda
b
lemon juice
c
window cleaner
d
drain cleaner

Answer 1

Based on the behavior of the red cabbage pH indicator as described in your passage, we can infer the following:

• Highly acidic solution: Bright red (indicates low pH)
• Moderately acidic solution: Pinkish (indicates slightly higher, but still low pH)
• Neutral solution (around pH 7): Reddish-purple
• Moderately basic solution: Bluish (indicates rising pH)
• Highly basic solution: Yellow (indicates high pH)

Now, we rationalize the household solutions:

• Club soda: This is typically slightly acidic due to dissolved carbon dioxide, so it would likely produce a red or pinkish color change.
• Lemon juice: This is also highly acidic, contributing to a bright red color.
• Window cleaner: Many window cleaners contain ammonia, which can be moderately basic, possibly turning the cabbage indicator bluish.
• Drain cleaner: Typically, drain cleaners are very basic due to caustic soda (sodium hydroxide) or similar compounds, leading to a yellow color change.

Given this information, the household solution most likely to have the highest pH would be:

d) drain cleaner

This is because it is typically a highly basic solution, which would change the color of the cabbage indicator to yellow, indicating a high pH.