The pH reading of a glass of liquid is given. Find the hydrogen ion concentration of the liquid.

Question

The pH reading of a glass of liquid is given. Find the hydrogen ion concentration of the liquid. (Give your answers in scientific notation, correct to one decimal place.)

 

Beer: pH = 4.5
[H+] = _________ × 10^--   M

Water: pH = 7.4
[H+] = _________× 10^--     M

Answer 1

The equation for pH is: pH = -log[H⁺], where [H+] is the concentration (in molar, aka mol/L) of the H⁺ ion.

 

If you need to solve for [H+], you will need to solve the equation for it first... so you first need to move the minus sign to the other side to isolate the log[H+]:

 

-pH = log[H⁺]

 

Then you need to take the antilog of both sides, which is simply applying 10^ on both sides, so you have:

 

10^(-pH) = 10^(log[H⁺])

 

Since 10^log = 1, you have

 

10^(-pH) = [H⁺]

 

In you calculator, simply type 10^-#, where # is the value of the pH give to you.

 

For example, if the pH were 3.5, the [H⁺] = 10^-3.5.... 3.16E-4.... or 3.16 x 10^–4... the E on the calculator means "x10^".

 

Be careful to use the small (-) sign on your calculator (bottom right by the "." on a TI calculator) in front of the 3.5... Using the large (–) minus sign will probably lead to an error message.

 

You have the tools, now you can do the math.