Calculate the [H3O+] and [OH-] concentrations in a 0.75 M solution of HBr

Answer 1

Great question!

The first step is identifying that HBr is a strong acid. Because we know it is a strong acid, we can assume all of the hydrogen ions bonded to the Br will dissociate. This means that the concentration of hydrogen ions, represented by [H₃O+], is equal to the concentration of HBr.

[H₃O+] = [HBr] = 0.75M

Now, we can calculate the pH of the solution with the equation pH = -log([H₃O+])

pH = -log(0.75) = .125

Clearly, this is a very acidic solution. This makes sense because we know that HBr is a strong acid. To calculate pOH, we can subtract the pH from 14, since pH + pOH = 14.

pOH = 14 - pH = 14 - (.125) = 13.875

Now we can calculate the [OH-] concentration by using the equation pOH = -log([OH-]), a similar equation to the one used earlier for pH.

13.875 = -log([OH-])

-13.875 = log([OH-])

10^-13.875 = [OH-]

[OH-] = 1.33 * 10^-14

Clearly, the concentration of [OH-] is very, very small. Again, this makes sense because HBr is a strong acid.

Hope this helps!