Week 3&4: Chemical Characteristics of Water Flashcards
What is the purpose of using chemical indicators in water?
To determine the presence of organics/ non-organics and their impact on water quality
List some typical cations
Ca2+, Mg2+, Na+, K+
List some typical anions
CO3 2-, HCO3-, SO4 2-, Cl-, NO3-
Describe Arsenic and its risk in water
Occurs naturally in geologic formations. Used in timber treatment and pesticides. Been linked to lung and bladder cancer
Describe Chloride and its effect in water
Its presence in water from leaching of sedimentary deposits, brine, or industrial/domestic wastes. Causes noticeable taste in water.
Describe iron and its effect in water
Its presence in water from iron in geologic material. Causes reddish colour in water and affects taste
Describe lead and its risk in water
Primarily from corrosion of pipes. Interferes with red blood cell formation, kidney damage, impacts cognition
Describe Manganese and its effect in water
Naturally occuring or from discarded batteries, steel production, agricultural products. Stains water and causes medicinal taste
Describe Sodium and its risk in water
Often comes from home water softeners. Can affect people suffering from heart, kidney or circulatory ailments
Describe Sulfate and its effect in water
Come from leaching of natural deposits. May cause laxative effects
Describe Zinc and its effect in water
May come from ore deposits. Can cause undesirable taste in water
Describe Nitrates/Cyanides and their risk in water
Nitrate can cause infant cyanosis or “blue baby syndrome. Cyanides tie up hemoglobin sites resulting in oxygen deprivation - cyanosis.
Describe toxic heavy metals and their risk in water
Arsenic, barium, cadmium, lead, mercury, etc. May be acute poisons or cause chronic disease
What happens to inorganic compounds when placed in water?
They dissociate into ions
What is valence?
The combining power of an element based on that of a hydrogen value (e.g. Na+ =1 and Cl- = -1)
What is the relationship for meq/L?
meq/L = mg/L * valence/atomic weight
What is the formula and units for Equivalent Weight (EW)?
EW = atomic weight/valence OR atomic weight/e-charge. The units are g/eq
When doing a graphical representation of water analysis, what is the typical order of cations?
Ca2+, Mg2+, Na+, K+, etc.
When doing a graphical representation of water analysis, what is the typical order of anions?
HCO3-, SO4 2-, Cl-, etc.
Sum of Cations = ?
Sum of Anions
What are three major inorganic constituent indicators?
- pH
- Alkalinity
- Hardness
Define pH
A measurement of the acid-base properties of a solution. pH<7 = acid. pH>7 = base
pH = -log[H+]
Define Alkalinity and what it’s important for
A measure of the water’s capacity to neutralize acids
- ability to absorb H+ without significant pH change
- important for chemical and biological processes
What are the major acids of alkalinity?
Bicarbonate (HCO3-), Carbonate (CO3 2-), Hydroxide (OH-)
Define equation for Total Alkalinity (meq/L)
TA = (HCO3-) + (CO3 2-) + (OH-) - (H+)
How do you convert meq/L of substance to mg/L as CaCO3?
meq/L * 50 mg/meq = mg/L CaCO3
How do you convert concentration of species from mg/L to meq/L?
- Find MW of species
- Divide MW by valence to get EW
- Divide concentration of species by EW to get meq/L
How can alkalinity be determined experimentally?
Using a titration with H2SO4
Describe the two stages of a titration
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
What is included in T-alkalinity?
Means total alkalinity, so includes the p-alkalinity. Equals volume of acid added for both stages of titration.
What is Hardness?
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.
What are the most abundant cations that contribute to hardness?
Calcium and Magnesium
Does total hardness include cations such as Na+?
No, total hardness is a combination of Ca2+ and Mg2+ since Na+ is not a multivalent cation.
What is the most abundant form of hardness and how does it occur?
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.
What are the the two types of hardness?
- Carbonate (Temporary) Hardness
- Non-carbonate (Permanent) Hardness
What is Carbonate Hardness (CH)?
It’s associated with HCO3- and CO3 2-. It can easily be removed by heating.
What is Non-Carbonate Hardness (NCH)?
Associated with other anions. It is not easily removed by heating.
What happens if alkalinity is greater than total hardness?
NCH = 0
What does TOC stand for?
Total Organic Carbon
What are the major sources of TOC in raw water?
- Natural organic material (NOM)
- synthetic organic compounds (SOC)
How are Synthetic organic compounds produced?
- chemical reaction during treatment
- originating from human activities
What is NOM?
- proteins, carbs, lipids etc.
- originates from degredation of plant/animal material
How does NOM affect Disinfection as a water treatment process?
It reacts with and consumes disinfectants which requires an increase in dosage
How does NOM affect Coagulation as a water treatment process?
It reacts with and consumes coagulants which requires an increase in dosage
How does NOM affect Adsorption in water treatment?
It adsorbs to activated carbon, depleting capacity of the carbon
How does NOM affect Membranes in water treatment?
It clogs membranes leading to a decline in water passability
How does NOM affect Distribution systems in water treatment?
Leads to corrosion and slime growth in the system
What are DBP’s when discussing synthetic organic compounds?
Disinfection byproducts
What are the two most common DBP classes?
THM’s and HAA’s
What are four ways NOM is removed in water?
- coagulation
- filtration
- dissolved air flotation
- adsorption, oxidation, ion exchange
