Basics

Question 1

List 6 common cations in drinking water (and their charges)

Answer 1

Sodium Na (+)
Potassium K (+)
Hydrogen H (+)
Calcium Ca (2+)
Magnesium Mg (2+)
Iron Fe (2+)

Manganese Mn (2+)

Question 2

List 6 common anions in drinking water (and their charges)

Answer 2

Chloride Cl (-)
Fluoride Fl (-)
Hydroxide OH (-)
Bicarbonate HCO_3 (-)
Carbonate CO_3 (2-)
Sulphate SO_4 (2-)

Question 3

Concentration (density) can be written as Molarity or Mass concentrations. What are the units for both?

Answer 3

Molarity [mol/L]

Mass [mg/L]

Question 4

How do you convert between mass concentration and molar concentration?

Answer 4

mass = molarity * molar weight

[mg/L] = [mmol/L]*[mg/mmol]

Question 5

What is water activity?

Answer 5

Activity describes the availability for reaction, or the amount of chemical per volume.

At low concentration, activity = concentration.

Question 6

What is the general formula for the equilibrium constant Keq?

Answer 6

K = (C.product1 * C.product2 * …) / C.reagent

Question 7

pKeq means what?

Answer 7

-log10(Keq)

Question 8

Large Keq favours what?

Answer 8

Products

Question 9

Do strong acids have a large K value or small?

Answer 9

Strong acids = Large K

Question 10

Autoionisation of water is described by the equilibrium constant Kw.

Kw =

Answer 10

Kw = [H_3O+][OH-]

Question 11

In equilibrium chemistry, pure solids and liquids have what value?

Answer 11

1

Question 12

In a neutral solution at 25°C, what are the concentrations of [H_3O+] and [OH-]?

Answer 12

[H_3O+] = [OH-] = 1.0*10^-7 M

Question 13

At 25°C, [H_3O+] *[OH-] = ?

Answer 13

1.0*10^-14 M

Question 14

What are the following short for?
pH
pOH
pKw

Answer 14

pH = -log10 H+
pOH =-log10 OH-
pKw = -log10 Kw

Question 15

a pH of zero indicates what?

Answer 15

Very strong acid

Question 16

a pOH of 14 indicates what?

Answer 16

Very strong acid

Question 17

pH + pOH = ?

Answer 17

14

Question 18

Describe the ratio of [H_3O+] and [OH-] when:

pH = 7
pH > 7
pH < 7

Answer 18

pH = 7 [H_3O+] = [OH-]
pH > 7 [H_3O+] < [OH-]
pH < 7 [H_3O+] > [OH-]

Question 19

A solid is equal to what value in equilibrium definitions?

Answer 19

1

Question 20

What are hard water characteristics?

Answer 20

Does not lather well and forms deposits.

Question 21

What causes hard water?

Answer 21

Presence of polyvalent cations such as Ca 2+ and Mg 2+ which come from the dissolution of minerals (often limestones such as Calcite and Dolomite).

Microbes in soil release CO2 via respiration, forming carbonic acid which dissolves limestone.

Question 22

What is alkalinity?

Answer 22

The capacity of water to resist changes in pH.

The ability to neutralise acid.

Question 23

What is alkalinity measured as?

Answer 23

CaCO_3 equivalent (becuase carbonate responsible for main buffering in natural water)

Question 24

What are the 2 reactions that buffer water in the alkaline process?

Answer 24

1: H_2CO_3 HCO_3(-) + H(+)
2: HCO_3(-) CO_3 (2-) + H(+)

RXN 1 replaces H+
RXN 2 consumes H+

Question 25

What is normality?

Answer 25

N = neutralising capacity [meq/L]

N = mass.c/Weq

e.g. A (2-) charge can neutralise 2H(+).

Question 26

What is equivalent weight?

Answer 26

Weq = MW/charge [mg/meq]

Question 27

What are the units for each:
MW
N
Weq
Mass Conc.
Molar Conc.

Answer 27

MW = [g/mol]
N = [meq/L]
Weq = [mg/meq]
Mass Conc. = [mg/L]
Molar Conc. = {mmol/L]