Answer:
To find the hydroxide ion concentration of a solution from its pH, we can use the equation:
pH + pOH = 14
where pOH is the negative logarithm of the hydroxide ion concentration [OH-]. We can rearrange this equation to solve for [OH-]:
pOH = 14 - pH
In this case, the pH of the solution is given as 4.75, so:
pOH = 14 - 4.75 = 9.25
Now, we can use the equation for the ion product constant of water Kw to find [OH-]:
Kw = [H+][OH-]
At room temperature (25°C), Kw is equal to 1.0 x 10^-14. Since HBr is a strong acid, it dissociates completely in water to form H+ and Br- ions. Therefore, the concentration of H+ in the solution is equal to the concentration of HBr, which we can find using the pH:
pH = -log[H+]
10^-pH = [H+]
10^-4.75 = 5.62 x 10^-5 M (rounded to 3 sig figs)
Now we can use Kw to find [OH-]:
Kw = [H+][OH-]
1.0 x 10^-14 = (5.62 x 10^-5)[OH-]
[OH-] = 1.78 x 10^-10 M (rounded to 3 sig figs)
Therefore, the hydroxide ion concentration of the HBr solution is 1.78 x 10^-10 M.