Question

Nitric acid (HNO3), a strong acid, is formed in the following reaction.

2 NO(g) + 3/2 O2(g) + H2O(g) → 2 HNO3(g).

Assume a volume of 22.4 mL of NO gas (at STP = 1 atm, 273 K) completely reacts with
excess of oxygen and water. If all of the acid that is formed is dissolved into 50. mL of
water, what should be the pH of the solution? (pH = - log[H+])?
A) 1.0
B) 1.7
C) 2.0
D) 3.0
E) 2.3

Answer 1

22.4 L are there in 1 mole of any gas

22.4ml= 22.4/1000L will be there in 22.4/1000*22.4= 0.001 moles

2 NO(g) + 3/2 O2(g) + H2O(g) → 2 HNO3(g).

2 moles of NO with excess oxygen and water gives 2 mole of HNO3

0.001 moles of NO gives 0.001*2/2=0.001 moles of HNO3

concentration of HNO3=moles/volume in L

volume =50ml= 50/1000L= 0.05

concentration of HNO3=0.001/0.05= 0.02

Since HNO3 is strong acid, it ionizes completely

hence HNO3+ H2O-------->H3O++ NO3-

pH= -log [H3O+]= -log (0.02)= 1.7 ( B is correct)