Video Transcript
For an aqueous solution at 25 degrees Celsius, the given equation can be applied. pH
plus pOH equals 14. What is the correct form of the equation when rearranged to have pH as the
subject?
The subject of an equation is the variable being worked out. The subject must be in the numerator, and it must be isolated on either side of the
equation. Our desired subject, pH, is in the numerator, but it is not isolated. This means that we will need to rearrange the formula. When rearranging a formula, we must remember that an operation performed on one side
of the equation must also be performed on the other side. And to move or cancel a variable, the opposite operation is performed on both sides
of the equation.
In the formula, our desired subject pH is being added to the variable pOH. To move the variable pOH and isolate pH, we must perform the opposite operation. This means that we need to subtract the pOH from the left side of the equation. But we must remember that this opposite operation must be performed on both sides of
the equation. So, we must subtract pOH from the right side of the equation as well.
This process has removed the variable pOH from the left side of the equation and has
transferred the variable to the right side of the equation. This gives us the formula pH equals 14 minus pOH. The variable pH is in the numerator and is isolated by itself on the left side of the
equation. This means that the equation pH equals 14 minus pOH is the correct form of the
equation when rearranged to have pH as the subject.
For the next question, I’ll keep the important pieces of information on the
screen.
The pH of a solution is found to be 11. What is the value of the pOH?
We are asked to solve for the pOH. This means that pOH is the subject of our equation. The variable pOH is in the numerator of our equation, but it has not yet been
isolated. The variables pH and pOH are added together in the equation. To isolate the pOH, we will need to perform the opposite operation and subtract the
variable pH from both sides of the equation. This process has moved the variable pH from the left side of the equation to the
right side of the equation. Now that we have isolated the pOH as the subject, we can substitute the pH given in
the question into the equation and solve for the pOH. A solution with a pH of 11 will have a pOH value of three.
