Finding pH and pOH. All help is appreciated?

Question

1) A solution has a hydrogen ion concentration of 1 x 10^-6M. What is its pH?

2) What is the pH of a solution if the [H+] = 7.2 x 10^-9M?

3) What is the pOH of a solution if the [OH-] = 3.5 x 10^-2M?

4) What is the pOH of a solution that has a pH of 3.4?

Answer 1

well pH is simply the -log of the concentration (in Molar) of H, so...

1) pH = -log(1e-6)
2) pH = -log(7.2e-9)

and pOH is the -log of the concentration of OH so...

3) pOH = -log(3.5e-2)

and pOH + pH = 14, so you know the pH and can figure out the pOH

Answer 2

A simple definition of pH is: pH = -log[H+], so:
1) pH = -log[1x10^-6] = 6
2) pH = -log[7.2x10^-9] = 8.14

Similarly for pOH = -log[OH-]:
3) pOH = -log[3.5x10^-2] = 1.46

You should also know that [OH-]*[H+] = Kw = 1x10^-14, so with that in mind:
4) 3.4 = -log[H+] **10 raised to values of both sides gets rid
10^-3.4 = [H+] ** of the logarithm on the right side**
3.98 x 10^-4 = [H+] then using the above equation
1x10^-14/3.98x10^-4 = [OH-] = 2.51 x 10^-11
and finally
pOH = -log[2.51 x 10^-11] = 10.6

or just use the fact that pH + pOH = 14
so pOH = 14-3.4 = 10.6

Answer 3

1. pH= -Log [H+]
pH= - Log[1x10-6] = 6
2. Same as above, but as a hint, split the problem into two parts, one with the exponent as in #1 and the other with the number.
pH = 9-Log(7.2)= 8.14 appx
3. Same deal as with pH
4. pH+pOH=14

Answer 4

all of them is pH = -log[H+]...pOH = -log[OH-]...pH+pOH=14
1. is .. pH = -log[1 x 10^-6]
2. pH = -log[7.2 x 10^-9]
3. pOH = -log[3.5 x 10^-2]
4. pOH = 14 - 3.4

i think.. can't exactly remeber ... highschool was long long time ago

Answer 5

pH = -log[H+]
pOH = -log[OH-]
[ ] meaning concentration of course

oh and just in case
14 = pH + pOH