Test question: Water has pH of 7. Which solution has a [H+] concen

[Lo.Lee.Ta.]

Test question: "Water has pH of 7. Which solution has a [H+] concen.."

1.

2. First of all, increasing [H+] concentration will give something more acidic. Since every jump between pH numbers is a 10 fold difference, I thought that to make a 100 fold difference, you would have to do 10x10, which would cause the pH number to go down by two steps.

That's why I chose A (bananas with a pH of 5).

The actual answer is B (milk with a pH of 6).

How does pH decrease by only 1 step?
Would you please explain this to me?

Thank you so much! :)

 

[Borek]

IMHO your answer (pH 5, bananas) is a correct one.

At pH 5 [H^+] = 10^{-5}, at pH 7 [H^+] = 10^{-7}, \frac {10^{-5}}{10^{-7}} = 100.