Question

Calculate the [OH−] value of each aqueous solution, Express your answer using two significant figures.

1) milk of magnesia with [H3O+]=2.5×10−9M.

2) aspirin with [H3O+]=6.5×10−4M.

3) pancreatic juice with [H3O+]=4.5×10−9M

Answer 1

1)

use:

[OH-] = Kw/[H3O+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

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

[OH-] = (1.0*10^-14)/(2.5*10^-9)

[OH-] = 4.0*10^-6 M

Answer: 4.0*10^-6 M

2)

use:

[OH-] = Kw/[H3O+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

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

[OH-] = (1.0*10^-14)/(6.5*10^-4)

[OH-] = 1.5*10^-11 M

Answer: 1.5*10^-11 M

3)

use:

[OH-] = Kw/[H3O+]

Kw is dissociation constant of water whose value is 1.0*10^-14 at 25 oC

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

[OH-] = (1.0*10^-14)/(4.5*10^-9)

[OH-] = 2.2*10^-6 M

Answer: 2.2*10^-6 M