Question

Which of the following solutions is the most basic ? 0.1 M HCI a solution PH=9.5 a solution POH=8.5 a solution with [OH-] = 1.0 x 10-11 M a solution with (H+) -1.0 x 10-6 M

Answer 1

1-

We know an acid is a species whoch has the ability lose H+ ion in the solution where as a Base has the ability to lose OH- ion.

Now the pH of the acids always < 7

where as pH of the bases always > 7

Again lower the pH value, stronger is the acid and higher the pH value, stronger is the Base

Again pH is calculated as the negative logarithm of [H+] concentration i.e

pH = -log[H+]

pOH = -log[OH-]

pH + pOH = 14

So for the given solutions-

i) 0.1 M HCl ----------> pH = -log[H+] = -log[0.1] = 1‬

ii) pH = 9.5

iii) pOH = 8.5

So pH = 14 - pH = 14 - 8.5 = 5.5‬

iv) [OH-] = (1.0 * 10^-11) M

So pOH = -log[OH-] = -log[1.0 * 10^-11] = 11

And pH = 14 - pH = 14 - 11 = 3

v) [H+] = (1.0 * 10^-6) M

So pH = -log[H+] = -log[1.0 * 10^-6] = 6

So the most basic solution having the highest pH is = [OH-] = (1.0 * 10^-11) M with pH = 11

2-

That formula to calculate equilibrium constant (K) is-

ΔG^o = -RT lnK

Where

R = Gas constant = 8.314 J/mole.K

T = Given kelvin temperature

= 25^oC

= 25 + 273

= 298 K

So putting the values in-

ΔG^o = -RT lnK

410000 J = - 8.314 J/mole.K * 298 K * lnK

lnK = (410000 J) / ( - 8.314 J/mole.K * 298 K)

= -165.48

K = e ^-165.48

= 1.35 * 10^-72