Formulas
Can I calculate the pH value of a substance?
Yes! But first you need a scientific calculator...
Ok now we can start! The pH of a substance determines how acidic or basic a substance is (more information here). To calculate the pH value of a substance use the formula...
pH= -log(H+)
*Note* that dash in front of the log is a negative sign!
For example:
*Note* on this website use "e" notation to represent scientific notation
A substance has 1.95 e -9 H+ solution. What will the pH be?
pH= -log(H+)
pH= -log (1.95e-9)
pH= 8.709
There are no units here!!
pH= -log(H+)
*Note* that dash in front of the log is a negative sign!
For example:
*Note* on this website use "e" notation to represent scientific notation
A substance has 1.95 e -9 H+ solution. What will the pH be?
pH= -log(H+)
pH= -log (1.95e-9)
pH= 8.709
There are no units here!!
Can I calculate how many H+ ions are in a solution?
Yes! The number H+ ions are the acidic molecules in a solution. (More info here). To calculate the H+ concentration use the formula…
H+= 10^(-pH)
Or, on a standard scientific calculator...
H+= 2nd log (-pH)
When plugging this into a calculator press the 2nd button, then log and lastly plug in the H+.
For example:
A substance has a pH of 10.12. What is the H+ concentration?
H+= 2nd log (-pH)
H+= 2nd log(-10.12)
H+= 7.5e-12
There are no units here!!
The cool thing about this formula is that this and the pH formula are reversible!!
H+= 10^(-pH)
Or, on a standard scientific calculator...
H+= 2nd log (-pH)
When plugging this into a calculator press the 2nd button, then log and lastly plug in the H+.
For example:
A substance has a pH of 10.12. What is the H+ concentration?
H+= 2nd log (-pH)
H+= 2nd log(-10.12)
H+= 7.5e-12
There are no units here!!
The cool thing about this formula is that this and the pH formula are reversible!!
What about the pOH scale?
The pOH scale is the opposite of the pH scale. (Click here for more info on pOH scale) To calculate the pOH value of a substance use this formula...
The formula looks like this:
pOH= -log(OH-)
For example:
A substance has 2.82 e -8 OH- ions. What would the pOH be?
pOH= -log(OH-)
pOH= -log (2.82 e -8)
pOH= 7.55
Forgot what the pOH scale is? Click here
The formula looks like this:
pOH= -log(OH-)
For example:
A substance has 2.82 e -8 OH- ions. What would the pOH be?
pOH= -log(OH-)
pOH= -log (2.82 e -8)
pOH= 7.55
Forgot what the pOH scale is? Click here
Can I calculate how many OH- ions are in a solution?
Of course you can! The OH- ions are the basic molecules in a solution. To calculate the OH- use this formula
OH-= 10^(-pOH)
When plugging this into a scientific calculator use...
OH-= 2nd log (-pOH)
For example:
A solution has a pOH of 8.61. What is the OH- concentration?
OH-= 2nd log(-pOH)
OH- = 2nd log(-8.61)
OH-= 2.45 e -9
The cool thing about this formula is that this and the pOH formula are reversible!!
OH-= 10^(-pOH)
When plugging this into a scientific calculator use...
OH-= 2nd log (-pOH)
For example:
A solution has a pOH of 8.61. What is the OH- concentration?
OH-= 2nd log(-pOH)
OH- = 2nd log(-8.61)
OH-= 2.45 e -9
The cool thing about this formula is that this and the pOH formula are reversible!!
Are there any shortcuts I can use?
For a given substance pH and pOH will always add up to 14!
The formula looks like this:
pH + pOH=14
For example:
I have a bottle of orange juice with a pH of 4.5. What is the pOH of the orange juice?
pH + pOH =14
4.5 + pOH = 14
14-4.5= pOH
pOH= 9.5
The formula looks like this:
pH + pOH=14
For example:
I have a bottle of orange juice with a pH of 4.5. What is the pOH of the orange juice?
pH + pOH =14
4.5 + pOH = 14
14-4.5= pOH
pOH= 9.5
So, if I have only the pH (or H+ or pOH or Oh-) I can find everything else?
Yes! So if you are given only the pH of a substance, you can first find the H+ of a solution using H+= 10^(-pH). From there, you can find the pOH using pH+pOH=14. Lastly, you can find the OH- concentration by using
OH= 10^(-pOH.) When completing these types of problems…
OH= 10^(-pOH.) When completing these types of problems…