Question

Calculate the ph and the poh of an aqueous solution that is 0.030 m in hcl(aq) and 0.070 m in hbr(aq) at 25°c.

Answer 1

Solution:

Since, both are strong acids. So both ionize 100% in solution.  

Let us consider that we have 1 liter of the solution. In it, we have 0.030 moles of H+ (from the HCl) and 0.070 moles of H+ (from the HBr) for a total of 0.100 mole in 1 liter. Here we ignore the chloride ion and the bromide ion since both acids ionize 100%. The only important ion (for pH) is the H+.  

In terms of just the H+, this is 0.100 M  

pH = - log 0.100 = 1.000  

And

pH + pOH = 14.000  

-1.000+14.000=13.000

Therefore,

pOH = 13.000

Answer 2

pH is the measure of the hydrogen ion concentration while pOH is of hydroxide ion concentration in the solution. The pH is 1 and pOH is 13.00.

What are pH and pOH?

pH is the concentration of the hydrogen ion released or gained by the species in the solution that depicts the acidity and basicity of the solution.

pOH is the concentration of the hydroxide ion $(\rm OH^{-})$ in the solution and is dependent on the pH as an increase in pH decreases the pOH and vice versa.

Both HCl and HBr are strong acids and gets ionized 100 % in the solution. If we let 1 L of solution for the acids then the concentration of the hydrogen ion will be 0.100 M.

pH is calculated as:

$\rm pH = - log [H^{+}]$

Substituting values in the equation:

$\begin{aligned}\rm pH &= \rm - log [H^{+}]\\\\&= \rm -log (0.100)\\\\&= 1.0 \end{aligned}$

pOH is calculated as:

$\rm pH + pOH = 14$

Substituting values in the equation above:

$\begin{aligned} \rm pH + pOH &= 14\\\\\rm pOH &= 14 - 1.00\\\\&= 13.00\end{aligned}$

Therefore, pH is 1 and pOH is 13.

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