How to calculate PH 1.9 =0.0126M

Question

I do not still understand. I want you step by step to calculate for me.

Thank you.

Answer 1

I do these this way.
pH = -log(H^+)
1.9 = -log(H^+)
-1.9 = log(H^+).
Now enter -1.9 on your calculator and hit the 10^x key. The answer of 0.01259 will appear.
This is just math. You may have seen it this way.
(H^+)= 10^-1.9
Enter 10, then y^x key, then -1.9, press = and the answer of 0.01259 will appear.

Answer 2

the answer is rounded off to 4 significant digits.