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

1. Feb 10, 2013

### 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! :)

2. Feb 10, 2013

### Staff: Mentor

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

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