Topic 8.3: The pH scale

Question 1

Why does water self-ionize?

Answer 1

Due to its amphoteric nature

Question 2

Chemical equation of ionization of water

Answer 2

2H2O(l) ⇌ H3O+(aq) + OH-(aq)

Question 3

Ionization constant of water (Kw)

Answer 3

Kw = [H+][OH-] = 1.0 x 10^-14

Question 4

Based on the relative concentrations of H+ and OH-, a solution is:

a) Neutral if…
b) Acidic if…
c) Basic if…

Answer 4

a) [H+] = [OH-]
b) [H+] > [OH-]
c) [H+] < [OH-]

Question 5

Formulas for calculating pH and pOH from their concentrations

Answer 5

a) pH = -log[H+]

b) pOH = -log[OH-]

Question 6

Formula for calculating pKw at 298 K

Answer 6

pKw = pH + pOH = 14.00

Question 7

Acidity of a solution when pH is:

a) = 7.00
b) < 7.00
c) > 7.00

Answer 7

a) Neutral
b) Acidic
c) Basic

Question 8

1 unit change in pH equals … in the H+ ion concentration

Answer 8

tenfold change

Question 9

Methods to measure pH (2)

Answer 9

a) Universal indicator

b) pH meter

Question 10

Functioning of universal indicator

Answer 10

The substance tested gives a distinct color, which is compared with a color chart supplied with the indicator

Question 11

Functioning of pH meter

Answer 11

The probe directly reads the [H+} concentration through a special electrode