Basics Flashcards
Basic Overview
List 6 common cations in drinking water (and their charges)
Sodium Na (+) Potassium K (+) Hydrogen H (+) Calcium Ca (2+) Magnesium Mg (2+) Iron Fe (2+)
Manganese Mn (2+)
List 6 common anions in drinking water (and their charges)
Chloride Cl (-) Fluoride Fl (-) Hydroxide OH (-) Bicarbonate HCO_3 (-) Carbonate CO_3 (2-) Sulphate SO_4 (2-)
Concentration (density) can be written as Molarity or Mass concentrations. What are the units for both?
Molarity [mol/L]
Mass [mg/L]
How do you convert between mass concentration and molar concentration?
mass = molarity * molar weight
[mg/L] = [mmol/L]*[mg/mmol]
What is water activity?
Activity describes the availability for reaction, or the amount of chemical per volume.
At low concentration, activity = concentration.
What is the general formula for the equilibrium constant Keq?
K = (C.product1 * C.product2 * …) / C.reagent
pKeq means what?
-log10(Keq)
Large Keq favours what?
Products
Do strong acids have a large K value or small?
Strong acids = Large K
Autoionisation of water is described by the equilibrium constant Kw.
Kw =
Kw = [H_3O+][OH-]
In equilibrium chemistry, pure solids and liquids have what value?
1
In a neutral solution at 25°C, what are the concentrations of [H_3O+] and [OH-]?
[H_3O+] = [OH-] = 1.0*10^-7 M
At 25°C, [H_3O+] *[OH-] = ?
1.0*10^-14 M
What are the following short for?
pH
pOH
pKw
pH = -log10 H+
pOH =-log10 OH-
pKw = -log10 Kw
a pH of zero indicates what?
Very strong acid
a pOH of 14 indicates what?
Very strong acid
pH + pOH = ?
14
Describe the ratio of [H_3O+] and [OH-] when:
pH = 7
pH > 7
pH < 7
pH = 7 [H_3O+] = [OH-]
pH > 7 [H_3O+] < [OH-]
pH < 7 [H_3O+] > [OH-]
A solid is equal to what value in equilibrium definitions?
1
What are hard water characteristics?
Does not lather well and forms deposits.
What causes hard water?
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.
What is alkalinity?
The capacity of water to resist changes in pH.
The ability to neutralise acid.
What is alkalinity measured as?
CaCO_3 equivalent (becuase carbonate responsible for main buffering in natural water)
What are the 2 reactions that buffer water in the alkaline process?
1: H_2CO_3 HCO_3(-) + H(+)
2: HCO_3(-) CO_3 (2-) + H(+)
RXN 1 replaces H+
RXN 2 consumes H+
What is normality?
N = neutralising capacity [meq/L]
N = mass.c/Weq
e.g. A (2-) charge can neutralise 2H(+).
What is equivalent weight?
Weq = MW/charge [mg/meq]
What are the units for each: MW N Weq Mass Conc. Molar Conc.
MW = [g/mol]
N = [meq/L]
Weq = [mg/meq]
Mass Conc. = [mg/L]
Molar Conc. = {mmol/L]
