##pH## is a quantitative measure of the concentration of hydronium ion, ##H_3O^+## in aqueous solution.
Water is known to undergo autoprotolysis according to the following reaction:
##2H_2O(l) rightleftharpoons H_3O^+ + HO^-##
This equilibrium has been exhaustively studied and we write the equilibrium in the normal way,
##K_”eq”=([H_3O^+][HO^-])/([H_2O])##
Because ##[H_2O]## is LARGE, it can be assumed to be constant, and removed from the expression to give:
##K_w=[H_3O^+][HO^-]=10^-14## at ##298*K##
A temperature is specified, because the extent of reaction depends upon temperature, especially for a bond-breaking reaction. Now this is a mathematical expression, the which we can divide, multiply etc., provided that we do it to BOTH sides of the expression. One think we can do is to take ##log_10## of both sides for reasons that will become apparent later:
##log_10K_w=log_10{[H_3O^+][HO^-]}=log_10{10^-14}##
And thus, ##log_10[H_3O^+]+log_10[HO^-]=log_10{10^-14}##
But ##log_10{10^-14}=-14## by definition, and we can rearrange the given expression to give:
##14=-log_10[H_3O^+]-log_10[HO^-]##
Of course, by definition ##-log_10[H_3O^+]=pH## and ##-log_10[HO^-]=pOH##
So for water at ##298K##, ##pH+pOH=14##. This is the defining expression for acid base behaviour in water, and it is one with which you will get very familiar.
So to answer your question (finally!), ##pH## is a quantitative measure of the concentration of ##H_3O^+## (in water).
I apologize for going on so long, but you will need the given background if you don’t know it already.
Our website has a team of professional writers who can help you write any of your homework. They will write your papers from scratch. We also have a team of editors just to make sure all papers are of HIGH QUALITY & PLAGIARISM FREE. To make an Order you only need to click Ask A Question and we will direct you to our Order Page at WriteDemy. Then fill Our Order Form with all your assignment instructions. Select your deadline and pay for your paper. You will get it few hours before your set deadline.
Fill in all the assignment paper details that are required in the order form with the standard information being the page count, deadline, academic level and type of paper. It is advisable to have this information at hand so that you can quickly fill in the necessary information needed in the form for the essay writer to be immediately assigned to your writing project. Make payment for the custom essay order to enable us to assign a suitable writer to your order. Payments are made through Paypal on a secured billing page. Finally, sit back and relax.
About Writedemy
We are a professional paper writing website. If you have searched a question and bumped into our website just know you are in the right place to get help in your coursework. We offer HIGH QUALITY & PLAGIARISM FREE Papers.
How It Works
To make an Order you only need to click on “Place Order” and we will direct you to our Order Page. Fill Our Order Form with all your assignment instructions. Select your deadline and pay for your paper. You will get it few hours before your set deadline.
Are there Discounts?
All new clients are eligible for 20% off in their first Order. Our payment method is safe and secure.