[Moss]

1. 90mL of water is added to 10mL of HNO3 with pH2. What is the new pH?

so
step1.
convert pH to molL-1
ph^2= [H3O+]=10^-2 molL-1

step 2.
the known and unknown substances
C1=10^-2molL-1
C2=?

V1=90mL
V2=10mL

C1V1=C2V2

so 10^-2 * 90 = C2*10

so C2= 9/100

Not sure where to go from here.

the answer says ph=3

Thanks

[Borek]

so 10^-2 * 90 = C2*10

so C2= 9/100

You have confused initial with final.

Once it will be correct, just apply pH definition.

[Moss]

thanks
so now i got
C2=1/900
=1/10^3 *9 ??

[Borek]

Stop guessing, try to be systematic.

You have added 90 ml to 10 mL, what is the volume?

[sjb]

thanks
so now i got
C2=1/900
=1/10^3 *9 ??

No, 1/900 is not the same as 1/10³ * 9, also what is your final volume?

[Moss]

i got it

thanks