Calculate the hydronium ion concentration and the hydroxide ion concentration in blood, the pH of which is 7.3

Question

Does anyone know how to solve this? Thanks!

Could you show me how you got to your solutions? Like show me how it works out? I don't quite understand the solving process to get to the answer which is why I can't get to the answers. If I saw this one worked out I'd be able to do the rest of my example problems.

Answer 1

pH = -log([H+]) where [H+] is the hydronium ion concentration, so switch the equation around: [H+] = 10^(-pH). [OH-] is the hydroxide ion concentration, and [H+][OH-] = 10^(-14), so once you have [H+] you can get [OH-].

More on how to do this: Well, pH = -log([H+]) is just an equation you have to know. If you multiply each side by -1 and raise 10 to the power of what's on each side of the equation, you get 10^(-pH) = 10^(log[H+]), or 10^(-pH) = [H+] by logarithm rules. (If you don't understand why the log went away, don't worry about it; just memorize the last equation there.)

It tells you pH = 7.3 for blood, so you use that equation: 10^(-7.3) = [H+]. Use your calculator to get the numerical answer.

[H+][OH-] = 10^(-14) is also something you just have to know. Alternatively, you could remember that pH + pOH = 14, where pOH = -log([OH-]), just like the equation for pH. Since you've already solved for [H+], you can find [OH-] by rearranging [H+][OH-] = 10^(-14) to [OH-] = 10^(-14)/[H+] and plugging in the value for [H+]. The other option is to rearrange the pOH equation exactly like for the pH equation, and find [OH-] using pOH = 6.7 (which we know because pH + pOH = 14 always).

Answer 2

[H+] is 10 to the power of -7.3, and [OH-] is 10 to the power of -6.7, both answers being in mol dm-3.