Calculate the pH of 7.2 × 10-8 M HCl. Report your answer to the hundredths place. Next, What fraction of the total H in this solution is from the HCl? Report your answer to the hundredths place.
You need two ICE charts for this; i.e., one for the strong acid HCl and one for H2O.
HCl is a strong acid; therefore, it dissociates completely (100%).
.......HCl --> H^+ + Cl^-
I.....7.2E-8....0......0
C...-7.2E-8...7.2E-8...7.2E-8
E......0......7.2E-8..7.2E-8
........H2O --> H^+ + OH^-
I..............7.2E-8...0
C...............+x.....x
E...........7.2E-8+x....x
(H^+)(OH^-) = Kw
(7.2E-8+x)(x) = 1E-14
Solve this quadratic for x and (H^+) = 7.2E-8+x. Then pH from that.
fraction from HCl = (H^+) from HCl/total (H^+)
Post your work if you get stuck.
Thank you very much for the reply.
I was able to solve for X (X = 7.03E-8), which I added to that of HCl (Total = 1.405E-7) and was able to obtain the pH (6.85, assume this answer is deemed correct).
Here is my problem: I took the (H^+) from HCL (X?) and divided it by the (Total).
=(7.03E-8/1.405E-7)
I got an answer of: .5004 which when multiplied by 100 = 50.04%
That answer is incorrect, but I'm not sure where I have messed up.
I apologize, I saw my mistake, and used HCL (7.2E-8)/(Total) and got: 51.245%
This answer is still wrong, so now I am thoroughly confused.
I obtained 7.028E-8 for x. Add to 7.2E-8 = 1.4228E-8 for total. I would round that to 1.42E-7 and pH = 6.8468 which to the hundredths place is 6.85.
H^+ from HCl is not x. x is the H^+ from the ionization of H2O.
fraction from HCl = 7.2E-8/1.42E-7 = 50.70%. That's what I would report. I don't know when your prof rounds but if s/he rounds at the end then fraction is
(7.2E-8/1.4228E-7)*100 = 50.60%. In any case, however, I don't think the hundredths place is allowed since 7.2 only has two s.f. (unless you typed 7.20 as 7.2 :-).
pH of 7.2 × 10-8 M HCl? That's like finding a needle in a haystack, but I'll give it a try!
*picks up a magnifying glass*
After some detective work, I've found that the pH of 7.2 × 10-8 M HCl is approximately 7.14. Ta-da!
Now, let's calculate the fraction of the total H in this solution that is from the HCl. Hmm, this fraction business is quite tricky. Let me put on my math hat for a moment.
Okay, just let me crunch the numbers...
*does some mathematical acrobatics*
The fraction of the total H in this solution that is from the HCl is approximately 1.00. That means that the HCl contributes all the H in the solution. No need to share the limelight, HCl!
Hope that brings a smile to your face like I've got one on mine!
To calculate the pH of a solution, we use the formula:
pH = -log[H+]
where [H+] represents the concentration of hydrogen ions in the solution.
In this case, the concentration of HCl is given as 7.2 × 10^-8 M. Since HCl is a strong acid, it completely dissociates into hydrogen ions (H+) and chloride ions (Cl-) in water.
So, the concentration of [H+] is equal to the concentration of HCl, which is 7.2 × 10^-8 M.
Now, let's calculate the pH using the formula:
pH = -log(7.2 × 10^-8)
To calculate this using a calculator, take the negative logarithm of the concentration:
pH = -log(7.2 × 10^-8) = -(-7.14) = 7.14
Therefore, the pH of the solution is 7.14 (rounded to the hundredths place).
Now, let's calculate the fraction of the total H in the solution that is from HCl.
The molecular formula of HCl is HCl, which means it has one hydrogen atom (H) per molecule. HCl completely dissociates into H+ ions when dissolved in water.
The total concentration of hydrogen ions ([H+]) in the solution is based on the concentration of HCl, which is given as 7.2 × 10^-8 M.
The fraction of H from HCl in the solution is equal to:
[HCl] / [H+] = 7.2 × 10^-8 M / 7.2 × 10^-8 M = 1
Therefore, the fraction of the total H in the solution that is from HCl is 1, which means all the hydrogen ions come from HCl.