An acidic solution has pH 4. If it is made one thousand times less acidic, what will be the approximate new pH?
Answer and explanation
Correct answer: Seven
The governing concept is the logarithmic pH scale, where pH = −log[H+]. A tenfold decrease in hydrogen-ion concentration raises pH by one unit. A thousandfold decrease is 10^3, so the pH rises by three units: 4 + 3 = 7. Therefore option C is the approximate answer. Option A would represent greater acidity, option B ignores the change, and option D assumes a four-unit rise instead of three.
Frequently asked questions
What is the correct answer to this question?
Seven
Why is this the correct answer?
The governing concept is the logarithmic pH scale, where pH = −log[H+]. A tenfold decrease in hydrogen-ion concentration raises pH by one unit. A thousandfold decrease is 10^3, so the pH rises by three units: 4 + 3 = 7. Therefore option C is the approximate answer. Option A would represent greater acidity, option B ignores the change, and option D assumes a four-unit rise instead of three.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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