High institution Chemistry aid » Acid-Base Chemistry » Acids and Bases » Calculating pH and also pOH

Explanation:

Since salt hydroxide is a solid base, it will dissociate totally in water. This means that the concentration the the base will certainly be equal to the concentration of hydroxide ion after the reaction runs to completion.

You are watching: Does ph poh always equal 14

We can find the concentration that hydroxide ion via stoichiometry. One hydroxide ion is created from every molecule of salt hydroxide the dissociates.

Since we have the concentration of hydroxide ions, we have the right to solve for the pOH the the solution.

The concern asks united state to find the pH of the solution, so us will require to convert pOH to pH. To execute so, we simply subtract the pOH indigenous 14.

The pH of the solution is 12.3. Since sodium hydroxide is a strong base, it renders sense that the pH is over 7.

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### Example question #1 : Calculating p H and P oh

You space presented through a systems that has actually a pOH of 2.13. What is the pH of this solution?

Explanation:

pH and also pOH space the log concentrations that protons and also hydroxide ions, respectively.

The amount of pH and pOH is always 14. This is due to the fact that the product the proton concentration and also hydroxide concentration must always equal the equilibrium consistent for the ionization the water, i beg your pardon is same to

.

In this question, we recognize that the pOH is equal to 2.13, allowing us to resolve for the pH.

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### Example question #3 : Calculating ns H and P oh

What is the pH because that a 0.05M equipment of hydrochloric acid?

Explanation:

Hydrochloric acid is a solid monoprotic acid, an interpretation that it will certainly dissociate completely in solution and generate one proton native each mountain molecule. This means that a 0.05M systems of hydrochloric mountain will result in a 0.05M concentration that protons.

The equation because that pH is together follows:

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### Example concern #4 : Calculating p H and also P five

Hydrofluoric acid has actually a

value of
. What is the pH that a
solution of hydrofluoric acid?

Explanation:

Hydrofluoric mountain is a weak acid, definition that we will have to use an ice table in stimulate to uncover the pH the the solution.

The well balanced reaction because that hydrofluoric mountain in water is:

I: prior to the reaction proceeds, we have 0.04M of hydrofluoric acid. Because water is a liquid, its concentration is irregularity for the equilibrium expression. Over there are also no products yet made.

C: when the reaction will equilibrium, both the hydronium and fluoride concentration will have increased by one unknown concentration. Us will contact this increase

. Vice versa, the concentration the hydrofluoric acid concentration will have lessened by the very same amount, in this case
.

E: utilizing the equilibrium expression and making it same to the acid dissociation constant, we have the right to solve for

.

See more: Hs- Lewis Acid Or Base ? Is Hs A Lewis Acid Or Lewis Base

Note: because the worth for

is walking to it is in very little compared to the initial mountain concentration, we have the right to disregard the
in the denominator:

Keep in mind that

is equal to the concentration that hydronium ions currently in the solution.