Week 3&4: Chemical Characteristics of Water

Question 1

What is the purpose of using chemical indicators in water?

Answer 1

To determine the presence of organics/ non-organics and their impact on water quality

Question 2

List some typical cations

Answer 2

Ca2+, Mg2+, Na+, K+

Question 3

List some typical anions

Answer 3

CO3 2-, HCO3-, SO4 2-, Cl-, NO3-

Question 4

Describe Arsenic and its risk in water

Answer 4

Occurs naturally in geologic formations. Used in timber treatment and pesticides. Been linked to lung and bladder cancer

Question 5

Describe Chloride and its effect in water

Answer 5

Its presence in water from leaching of sedimentary deposits, brine, or industrial/domestic wastes. Causes noticeable taste in water.

Question 6

Describe iron and its effect in water

Answer 6

Its presence in water from iron in geologic material. Causes reddish colour in water and affects taste

Question 7

Describe lead and its risk in water

Answer 7

Primarily from corrosion of pipes. Interferes with red blood cell formation, kidney damage, impacts cognition

Question 8

Describe Manganese and its effect in water

Answer 8

Naturally occuring or from discarded batteries, steel production, agricultural products. Stains water and causes medicinal taste

Question 9

Describe Sodium and its risk in water

Answer 9

Often comes from home water softeners. Can affect people suffering from heart, kidney or circulatory ailments

Question 10

Describe Sulfate and its effect in water

Answer 10

Come from leaching of natural deposits. May cause laxative effects

Question 11

Describe Zinc and its effect in water

Answer 11

May come from ore deposits. Can cause undesirable taste in water

Question 12

Describe Nitrates/Cyanides and their risk in water

Answer 12

Nitrate can cause infant cyanosis or “blue baby syndrome. Cyanides tie up hemoglobin sites resulting in oxygen deprivation - cyanosis.

Question 13

Describe toxic heavy metals and their risk in water

Answer 13

Arsenic, barium, cadmium, lead, mercury, etc. May be acute poisons or cause chronic disease

Question 14

What happens to inorganic compounds when placed in water?

Answer 14

They dissociate into ions

Question 15

What is valence?

Answer 15

The combining power of an element based on that of a hydrogen value (e.g. Na+ =1 and Cl- = -1)

Question 16

What is the relationship for meq/L?

Answer 16

meq/L = mg/L * valence/atomic weight

Question 17

What is the formula and units for Equivalent Weight (EW)?

Answer 17

EW = atomic weight/valence OR atomic weight/e-charge. The units are g/eq

Question 18

When doing a graphical representation of water analysis, what is the typical order of cations?

Answer 18

Ca2+, Mg2+, Na+, K+, etc.

Question 19

When doing a graphical representation of water analysis, what is the typical order of anions?

Answer 19

HCO3-, SO4 2-, Cl-, etc.

Question 20

Sum of Cations = ?

Answer 20

Sum of Anions

Question 21

What are three major inorganic constituent indicators?

Answer 21

• pH
• Alkalinity
• Hardness

Question 22

Define pH

Answer 22

A measurement of the acid-base properties of a solution. pH<7 = acid. pH>7 = base

pH = -log[H+]

Question 23

Define Alkalinity and what it’s important for

Answer 23

A measure of the water’s capacity to neutralize acids

• ability to absorb H+ without significant pH change
• important for chemical and biological processes

Question 24

What are the major acids of alkalinity?

Answer 24

Bicarbonate (HCO3-), Carbonate (CO3 2-), Hydroxide (OH-)

Question 25

Define equation for Total Alkalinity (meq/L)

Answer 25

TA = (HCO3-) + (CO3 2-) + (OH-) - (H+)

Question 26

How do you convert meq/L of substance to mg/L as CaCO3?

Answer 26

meq/L * 50 mg/meq = mg/L CaCO3

Question 27

How do you convert concentration of species from mg/L to meq/L?

Answer 27

- Find MW of species - Divide MW by valence to get EW - Divide concentration of species by EW to get meq/L

Question 28

How can alkalinity be determined experimentally?

Answer 28

Using a titration with H2SO4

Question 29

Describe the two stages of a titration

Answer 29

If pH is > 8.3, then two stages carried out Stage 1: - titration is carried out until pH = 8.3 with phenophthalein as indicator (pink to colourless) - known as P-alkalinity where carbonate converted to bicarbonate, but bicarbonate not converted to carbonic acid Stage 2: - titration is carried out to pH = 4.5 with BCG as indicator (green to pink) - known as T-alkalinity where bicarbonate converted to carbonic acid

Question 30

What is included in T-alkalinity?

Answer 30

Means total alkalinity, so includes the p-alkalinity. Equals volume of acid added for both stages of titration.

Question 31

What is Hardness?

Answer 31

It is caused by multivalent cations (so 2+ or more), and causes a reduction in the cleaning action of soap as well as scaling in pipes, boilers, etc.

Question 32

What are the most abundant cations that contribute to hardness?

Answer 32

Calcium and Magnesium

Question 33

Does total hardness include cations such as Na+?

Answer 33

No, total hardness is a combination of Ca2+ and Mg2+ since Na+ is not a multivalent cation.

Question 34

What is the most abundant form of hardness and how does it occur?

Answer 34

Calcium Bicarbonate. It is picked up by rainwater containing carbonic acid which passes through limestone. It reacts with Calcium Carbonate in the soil to produce Calcium Bicarbonate.

Question 35

What are the the two types of hardness?

Answer 35

- Carbonate (Temporary) Hardness - Non-carbonate (Permanent) Hardness

Question 36

What is Carbonate Hardness (CH)?

Answer 36

It's associated with HCO3- and CO3 2-. It can easily be removed by heating.

Question 37

What is Non-Carbonate Hardness (NCH)?

Answer 37

Associated with other anions. It is not easily removed by heating.

Question 38

What happens if alkalinity is greater than total hardness?

Answer 38

NCH = 0

Question 39

What does TOC stand for?

Answer 39

Total Organic Carbon

Question 40

What are the major sources of TOC in raw water?

Answer 40

- Natural organic material (NOM) - synthetic organic compounds (SOC)

Question 41

How are Synthetic organic compounds produced?

Answer 41

- chemical reaction during treatment - originating from human activities

Question 42

What is NOM?

Answer 42

- proteins, carbs, lipids etc. - originates from degredation of plant/animal material

Question 43

How does NOM affect Disinfection as a water treatment process?

Answer 43

It reacts with and consumes disinfectants which requires an increase in dosage

Question 44

How does NOM affect Coagulation as a water treatment process?

Answer 44

It reacts with and consumes coagulants which requires an increase in dosage

Question 45

How does NOM affect Adsorption in water treatment?

Answer 45

It adsorbs to activated carbon, depleting capacity of the carbon

Question 46

How does NOM affect Membranes in water treatment?

Answer 46

It clogs membranes leading to a decline in water passability

Question 47

How does NOM affect Distribution systems in water treatment?

Answer 47

Leads to corrosion and slime growth in the system

Question 48

What are DBP's when discussing synthetic organic compounds?

Answer 48

Disinfection byproducts

Question 49

What are the two most common DBP classes?

Answer 49

THM's and HAA's

Question 50

What are four ways NOM is removed in water?

Answer 50

- coagulation - filtration - dissolved air flotation - adsorption, oxidation, ion exchange