The pH of a solution is 3. When its pH changes to 6, then the hydrogen ion concentration
- A.Increases 2 times
- B.Increases three times
- C.Decreases 100 times
- D.Decreases 1000 times
Correct answer
Explanation
The correct answer is D, decreases 1000 times. The pH is the negative logarithm of the hydrogen ion concentration, so each rise of one unit means the concentration has fallen to one tenth. A change from pH 3 to pH 6 is a rise of three units, which is ten multiplied by ten multiplied by ten, that is a thousandfold fall in hydrogen ions, and the solution becomes much less acidic. Options A and B are wrong for two reasons: a rise in pH always means fewer hydrogen ions, not more, and the change is never a simple doubling or tripling because the scale is logarithmic. Option C is wrong because a hundredfold fall would correspond to a change of only two units, say from pH 3 to pH 5. Keep in mind that the same rule works downward, so moving from pH 6 to pH 3 multiplies the hydrogen ion concentration a thousand times.
Read the full article: Acids, Bases and Salts: pH Scale and Common Salts
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