Question

The [H3O+] in a solution is increased to twice the original concentration. Which change could occur in the pH? 2.0 to 4.0 1.7 to 1.4 5.0 to 2.5 8.5 to 6.5 6.8 to 9.8

Answer 1

Answer: second option: 1.70 to 1.40

Explanation:

1) The definition and formula of pH is - log [H₃O⁺]

2) So, if the original concentration is x and the increased concentration is 2x, you get:

pHi = - logx

pHf = - log 2x = - log 2 - logx

⇒ pHf - pHi = - log2 - logx - (- logx) =  - log2 ≈ - 0.30

⇒ pHi - pHf =  0.30 This is the pH of the final solution (with double concentration of hydronium ions) is 0.30 points lower than the pH of the initial pH.

3) The only choice that shows a decrease of 0.30 in the pH is the second option: 1.70 to 1.40. So that is the answer.

Answer 2

The change that could occur in the pH in the situation, the [H3O+] in a solution is increased to twice the original concentration, is 1.70 to 1.40
 pH formula  is - log [H₃O⁺]



pHi = - logx
pHf = - log 2x = - log 2 - logx
- log2 ≈ - 0.30
pHi - pHf =  0.30 
So there is a decrease of 0.30.