PH and POH

[Reynaldo Fernandez 3L]

How do we know when to use PH or when to use POH. And also without a chemical reaction formula given how can we know if we need to use PH or POH? And what is the difference between the two in the answer?

[605775499]

pH is the minus log of the concentration of H3O+ ions in a solution.
pOH is the minus log of the concentration of OH- ions in a solution.

Converting between the two is easy because pOH+pH = 14.

Use whatever the question asks for, or gives you.
For example if you are given H3O+ concentration and asked to find pOH, you'd first find the pH, then do 14-pH to find the pOH.

The hard part would be finding pH when those aren't given.
For example K_A of an acid = a value, what is the pH if there is 0.XXM of this acid? (for example q1 on the hw).
In this case you'd set up K_A = [H][A]/[HA] where the inital HA is 0.XXM, and then you'd use an ICE table and the K_A value to solve for X, which would give you the concentration of H+ ions (H3O+) which you can use to find the pH.

[Marina Casagrande De Lucca 3L]

we use pH when we have H30+ (because pH=-log[H3O+]) one pOH when we have OH- (pOH=-log[OH-]).

Regarding the problems, it depends on what you're given and what they're asking of you. For example, if the question is asking about the pH but you are able to find the OH- concentration, use that to find the pH because pH+pOH=14.

I am unsure if I understand what you mean by the difference between the two in the answer, but the answer will depend on what is being asked (pH or pOH); therefore, the difference between them will be what I said above.

Hope this helps :)

[dylani]

pH is often used for acids or when we are computing from K_A, whereas pOH is when we are given bases or K_B values. pH and pOH are related however in that pH + pOH = 14, so you can convert easily between them. Based on information that is given in the problem you should be able to figure out if the compounds/solutions included in the reaction include weak acid or base, and if it is a weak acid you will use K_A and pH, and if it is a weak base you will use K_B and pOH. The difference is that pOH = -log₁₀ [OH^-] and pH = -log₁₀ [H₃O⁺]. pH is for hydronium ions whereas pOH is for hydroxide ions

[hannah]

pOH measures hydroxide through the negative log of its concentration, while pH is the negative log of H3O. When you are given a question with Ka, then you are likely going to be dealing with pH rather than pOH. Similarly, questions that provide base concentrations and Kb are probably associated with pOH.

[samaagwani-disc2L]

You calculate pH first when the problem gives you an acid. You would take the -log of [H3O+] to obtain the pH. Calculating the pOH from this point is very easy you just subtract the pH from 14 to obtain the pOH. Likewise, if the problem gives you a base, you take the -log of [OH-] to obtain the pOH. Then you do the same thing and subtract the pOH from 14 to obtain the pH. Hope this helps:)

[Caitlin_Chheda_1K]

Hi! I believe that pH is used when we are given an acid and need to calculate the concentration of H3O+ ions in solution. pOH is used when we are given a base and need to calculate the concentration of OH- ions in solution.

Normally, if there is no chemical reaction formula given, I will try to write one out to guide me based on the question.

[Jacqueline_Velasquez_14B]

hey!
basically pH deals with H3O+
and pOH deals with OH-

pH = -log [H30+]
pOH = -log [OH-]

[Elian L]

We use pH when we want to measure how acidic a solution is and pOH when we want to measure how basic it is. Without a chemical formula, you can choose pH or pOH based on whether you're dealing with an acid (use pH) or a base (use pOH). The difference is that pH measures acidity and pOH measures basicity. Hope this helps!