Question

Calculate the concentrations of H3O+ and the pH of each acidic solution. Since HCl is a monoprotic acid (an acid that donates only one proton or hydrogen atom permolecule to an aqueous solution), the H3O+ concentration is equivalent to the HCl molarity.
I'm working on a lab and need a little help getting the pH's. For the lab you had 7 test tubes, 6 filled with 9mL of distilled water and 1 tube filled with 5mL 0.1M HCl and 5mL distilled water. Then you took the #1 test tube added 1mL to #2, 1mL #2-#3, 1mL #3-#4, 1mL #4-#5, 1mL #5-#6,1mL #6-#7

Now i'm stuck trying to figure out the pH's.

Answer 1

In water:
HCl -> H+ + Cl-

HCl is a strong acid meaning it is roughly 100% in its dissociated form when dissolved in water

So in this case moles of HCl = Moles of H+
Therefore molarity of HCl = Molarity of H+

So all you need to do is use the formula

pH = -log[H+]

square brackets around an ion or molecule means molarity in chemistry

You will also need to multiply the Molarity of HCl by the ratio of original volume transferred over the new volume each time.

For example:

I take 1mL of 0.1M NaOH and add bring its volume up to 10mL with water

therefore the new concentration will be ,

(1mL/10mL)*0.1M = 0.01M

This answer makes sense because the concentration is going down which is expected when you dilute something, if you get a larger concentration you have the ratio inverted the wrong way.

Answer 2

this method also works for figuring out original concentrations, it is just based on,

C1V1 = C2V2 formula (look it up)

Answer 3

thanks!