Can you please tell me if these are right?

Determine the pH for the following solutions
A [OH-] = 1.0 X 10^-7 M
I got 7
B. [H3O+ = 4.2 X 10 ^-3M
I got 2.4
C. [H3O+]= 0.0001M
I got 4
D. [OH-] = 8.5 X10^-9M
I got 5.9

What are the [H3O+] and [OH-] for a solution with the following pH values?
a. 10.0
For [OH-] I got 1.0*10^-4. and [H3O+] a. 10.0 I get 1.0*10^-10

Thank you!

And could you please tell me how to figure this question out?

Solution X has a pH of 9.5 and solution Y has a pH of 7.5.
a. what solution is more acidic?
b. what is the [H3O+] in each?
c. what is the [OH-] in each?

1 answer

The first four are correct.

lower pH is more acid.

b. [H3O+]=log^-1 (9.5)=3.16E9
the antilog or log^-1 key might be the 10x key on your calculator.

pOH=14-pH=14-9.5=4.5
[OH-]=antilog (4.5)=3.2E4

Notice [OH][H}= 1E14, which offers another way to solve it.