Question

1. suppose you have already compared the ph values of two substances using 0–14 paper. when would a follow - up test using 4.5–7.5 paper be most helpful? when both substances had a ph value of about 3 on the 0–14 paper when both substances had a ph value of about 6 on the 0–14 paper when both substances had a ph value of about 9 on the 0–14 paper when one substance had a ph value of about 5 and the other substance had a ph value of about 7 on the 0–14 paper

Explanation:

The 4.5 - 7.5 pH paper is useful for getting more precise pH values within the 4.5 - 7.5 range. When the initial 0 - 14 paper shows pH values in this range, a follow - up with 4.5 - 7.5 paper is most helpful. Among the options, when both substances had a pH value of about 6 on the 0 - 14 paper, they are in the range where 4.5 - 7.5 paper would give more detailed information.

Answer:

when both substances had a pH value of about 6 on the 0 - 14 paper