How many parts of base are needed to adjust pH 3 back to pH 7?

• A. 100 parts of base
• B. 1,000 parts of base
• C. 10,000 parts of base
• D. 100,000 parts of base

Answer: (C)

To determine how many parts of base are needed to adjust a solution's pH from 3 to 7, it's useful to understand how the pH scale works. The pH scale is logarithmic, meaning each whole number change on the scale represents a tenfold change in acidity or alkalinity. A pH of 3 is considered highly acidic, while a pH of 7 is neutral.

In moving from pH 3 to pH 7, you are increasing the pH by four units: from 3 to 4, then from 4 to 5, then 5 to 6, and finally from 6 to 7. Since the scale is logarithmic:

• Going from pH 3 to pH 4 requires 10 times more base.

• From pH 4 to pH 5 requires another 10 times more base.

• From pH 5 to pH 6 requires yet another 10 times more base.

• From pH 6 to pH 7 requires one more 10 times more base.

Overall, to calculate the total amount of base needed to adjust from pH 3 to pH 7, you multiply the required adjustments: