Chemistry
posted by Natasha .
How many grams of nitric acid (HNO3) must be dissolved in 740 mL of water to make a solution with a pOH = 8.3?

The system N2O4 <>2NO2 maintained in a closed vessel at 60º C & a pressure of 5 atm has an average (i.e. observed) molecular weight of 69, calculate Kp.
At what pressure at the same temperature would the observed molecular weight be (230/3) 
plz answer mine
The system N2O4 <>2NO2 maintained in a closed vessel at 60º C & a pressure of 5 atm has an average (i.e. observed) molecular weight of 69, calculate Kp.
At what pressure at the same temperature would the observed molecular weight be (230/3) 
just change the value
i found it on y!A
find the [H+} in pH of 4.5 ,
10^4.5 =
[H+] = 3.16 e5 molar
find the moles acid in 350 ml
0.350 litres @ 3.16 e5 mol/litre =
1.11 e5 moles of HNO3
find the grams using molar mass:
1.11 e5 moles of HNO3 @ 63 g/mol =
0.00070 grams of HNO3
======================================…
@ pH of 2.9, find the H+:
10^2.9 =
0.00126 molar H+
use the dilution formula:
C1V1 = C2V2
(4.2M) V1 = (0.00125M) (500ml)
V1 = 0.15 ml of 4.2 Molar is required 
see same question
how many grams nitric acid HNO3 must be dissolved in 350 ml water to make a solution with pH of 4.5"?
or "how many ml of a 4.2M nitric acid solution are required to make 500 ml of solution with pH of 2.9