Chapter U6, Problem 4STP

Interpretation Introduction

Interpretation:

The pH of cabbage indicator when it turns red needs to be determined.

Concept introduction:

An indicator is a substance which changes its color when placed in acidic and basic solutions.

Red cabbage is a natural indicator which turns its color in acids and bases.

In acids, it turns red and in bases it turns bluish green.

pH of acidic solutions is less than seven.

pH of basic solutions is greater than seven.

Answer to Problem 4STP

Option (A) 2 is the answer.

Explanation of Solution

Reason for correct option:

Cabbage solution turns red in acidic solutions.

Acids have pH less than seven.

Bases have pH greater than seven.

Neutral solutions have pH is equal to seven.

So, among the given options, option (A) is the correct answer.

Red cabbage indicator is represented as follows:

Conclusion

Reasons for incorrect options:

Acids have pH less than seven.

Bases have pH greater than seven.

Neutral solutions have pH is equal to seven.

Among the given options, option (B) has pH seven, which indicates a neutral solution.

(C) This option has pH 9 which indicates the solution is basic and the indicator color should be bluish green and not red. So, this is also a wrong option.

(D) This option has pH 9 which indicates the solution is basic and the indicator color should be bluish green and not red. So, this is also a wrong option.

Hence, option (A) is the correct answer.