Question

For each strong acid solution, determine [H3O+],[OH−] , and pH . A solution that is 0.860% HNO3 by mass (Assume a density of 1.01 g/mL for the solution.)

Answer 1

Let volume of solution be 1 L

volume , V = 1 L

= 1*10^3 mL

density, d = 1.01 g/mL

mass = density * volume

= 1.01 g/mL *1*10^3 mL

= 1010.0 g

This is mass of solution

mass of HNO3 = 0.86 % of mass of solution

= 0.86*1010.0/100

= 8.686 g

Molar mass of HNO3,

MM = 1*MM(H) + 1*MM(N) + 3*MM(O)

= 1*1.008 + 1*14.01 + 3*16.0

= 63.018 g/mol

mass(HNO3)= 8.686 g

number of mol of HNO3,

n = mass of HNO3/molar mass of HNO3

=(8.686 g)/(63.018 g/mol)

= 0.138 mol

volume , V = 1 L

Molarity,

M = number of mol / volume in L

= 0.138/1

= 0.138 M

This is concentration of acid.

[H3O+] = 0.138 M

use:

pH = -log [H+]

= -log (0.138)

= 0.860

use:

[OH-] = (1.0*10^-14)/[H3O+]

[OH-] = (1.0*10^-14)/(0.138)

[OH-] = 7.25*10^-14 M

Answer:

[H3O+] = 0.138 M

[OH-] = 7.25*10^-14 M

pH = 0.860