Question

What is the pH of each of the following solutions?
a) 5.0 x 10^-4 M HCL
b) 5.0 x 10^-4 M KOH
c) 0.15 M HCL
d) 1.5 x 10^-2 M NaOH

@photon336

Answer 1

First thing you need to know is the hydronium ion concentration of the solution, which you can find from the concentration of the acid or base in that solution. To do that, you need to know whether they are strong (fully dissociate in sufficient water) or weak. Do you know that for the three listed here?

Answer 2

HCl = strong acid
KOH = strong base
NaOH = strong base

Answer 3

Okay, good. That makes things easier. Each molecule of those will dissociate and give us an equivalent concentration of either H+ for the acid or OH- for base. We plug that into the pH formula to get our pH

Answer 4

so when they completely dissociate their concentrations with be the same for [H] and [OH]

Answer 5

so, if our strong acid is 0.1 M HCl, for example, our [H3O+] value will be 0.1, and our pH can be calculated by

\[pH = -\log_{10} [H_3O^+] = -\log_{10} 0.1 = 1\]

Answer 6

ahhh okkay

Answer 7

for the bases, we can use \[pOH = -\log_{10} [OH^-]\] and \[pH = 14 - pOH\]

Answer 8

so for a.
\[pOH = -\log_{10} \left[ 5.0 \times 10^{-4} \right] \]
\[pOH = 3.30\]
pH = 14 - pOH
pH = 14 - 3.30
pH = 10.7

Answer 9

That's my understanding, yes.

Answer 10

that's b), not a)...

Answer 11

a would be 3.30

Answer 12

yes

Answer 13

c. would be

\[pH = -\log_{10} \left[ .15 M \right] \]
pH =0.82 ?

Answer 14

d.
pOH=−log[1.5×10^-2]
pOH=1.82
pH = 14 - pOH
pH = 14 - 1.82
pH = 12.18

Answer 15

log base 10 of a number is the power to which 10 must be raised to get it. \[10^{-1} = 0.1\]so \[\log_{10} 0.1 = -1\]right? That means our log should be somewhere in that ballpark, and after we take the negative of the value of the log, we should have a positive number for the pH, yes?

Answer 16

(I'm talking about c) here)

Answer 17

how would i calculate that with my calculator? what would I plug in

Answer 18

10^.15

Answer 19

sorry, I misread your answer, I read the = as a -, my bad!

Answer 20

you'll be old someday, too :-)

Answer 21

so, so far I have solved a, b, and d, but c is wrong still?

Answer 22

the answer for c is pH 0.82 as you said. I just misread it and thought you had given -0.82

I agree with all of your answers.

Answer 23

yay!