The formula in getting the hydrogen -ion concentration [H+] is:
− pH = log [H+]
[H+] = 10^−pH
We have the pH level of the tomato juice that is 4.2
[H+] = 10^−pH
[H+] = 10^-4.2
[H+] = 0.0000630957
[H+] = 6.30957 x 10^-5
So the hydrogen -ion concentration [H+] for tomato juice with pH level of 4.2 is 6.30957 x 10^-5.