PTEC 107 Process Science
Spring, 2012
Session 3 – General Chemistry Pt 1
Topics
Definition of terms
 Chemical formulas
 Chemistry background
 Reactions
 Equilibrium and law of mass action
 pH and acid base reactions
 Coagulation
 Water constituents
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Definition of terms
Inorganic chemistry
 Organic chemistry
 Atomic structure – protons, neutrons,
electrons
 Atoms and molecules
 Elements and compounds
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Chemical formulas
Shorthand notation to express which
elements are in a molecule and in what ratio
 For example, Fe2O3 has 2 atoms of iron (Fe)
for every 3 atoms of oxygen (O)
 If atoms are ionized, they are combined to
produce a neutrally charged molecule
 Use your handout to explain what atoms are
in each of the molecules on the following page
and in what ratio
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Chemical formula exercise
· CO
· CH4
· CO2
· H2O
· HNO3
· H2SO4
· NaOH
· CaO
· Ca(OH) 2
· SO2
· N2
· MgO
· HF
· CaCO3
· C2H2
· C2H4
· C2H6
· H3 (PO)4
· ZnO
· P2O5
· H2S
Chemical equations
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Composed of chemical formulas
Show the proportions in which molecules or atoms
react to form products
Reactants are shown on left hand side and products
on right hand side
Numbers before chemical formula signify the number
of molecules that go into the reaction
The same number of atoms of a species will be on
both sides of the equals sign
For example, ZnS + 2HNO3 = Zn(NO3)2 + H2S
Chemical equation exercise
For the reactions on the following slide explain:
 what the reactants and products are
 what the ratio these molecules are in
Balance the following equations so that there is
the same number of atoms of a species in the
products as there is in the reactants
Chemical equation exercise
CH4 + O2 = CO2 + H2O
 H2SO4 + NaOH = Na2SO4 + H2O
 CH3 SH + H2 = CH4 + H2S
 C6H6 + H2 = C6H14
 C7H16 = C3H6 + C4H8 + H2
 Fe + O2 = Fe2O3
 FeS + O2 = Fe2O3 + SO2
 Ca(OH)2 + H2SO4 = CaSO4 + H2O
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Chemical equations
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Chemical equations can also help you determine the amount
of reactants to combine to produce a desired amount of
products
Each molecule combines with the others in terms of its
molecular weight
For example, one molecular weight of NaOH would combine
with one molecular weight of HCl to obtain one molecular
weight each of NaCl and H2O based upon the following
chemical equation
NaOH + HCl = NaCl + H2O
Chemistry Background
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Atomic and molecular weight (tabulated)
Atoms combine to form molecules
 Obtain atomic weights or mass from chart (next
slide) or from the following website
http://www.chemicalelements.com/
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A nice website with a lot of interactive
information on chemistry is
http://serendip.brynmawr.edu/sci_edu/chemsit
es.html
Chemistry Background
Determine the molecular weight of a compound
 Molecular weight is the sum of the: number of atoms times the atomic
weight (mass) for each
 The number of atoms is shown in the chemical formula – i.e. H2O has
two atoms of hydrogen and one of oxygen
 NaCl molecular weight is 1*23 + 1*35 = 58
 Ferrous Sulfate, Fe2(SO4)2, molecular weight is: 2 * 55.8 + 2 * (1*32.1 +
4 * 16) = 303.8
 Units are grams/gram mole or pounds/pound mole
 Used to calculate amounts of chemicals to prepare solutions for
analysis or for processes
 Determine the molecular weights of the reactants and products in
each of the reactions in the following slide. (You may need to balance
the equations first.)
Chemical equation exercise
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CH4 + O2 = CO2 + H2O
H2SO4 + NaOH = Na2SO4 + H2O
CH3 SH + H2 = CH4 + H2S
C6H6 + H2 = C6H14
C3H8 + C4H10 = C7H16 + H2
C7H16 = C3H8 + C4H8
Fe + O2 = Fe2O3
FeS + O2 = Fe2O3 + SO2
Ca(OH)2 + H2SO4 = CaSO4 + H2O
Reaction Types
Precipitation (removal of phosphate)
 Oxidation or reduction (CH4 combustion)
 Neutralization (addition of an acid to
neutralize a base or vice versa)
 Decomposition reactions – breaking one
molecule into two or more products (like
catalytic cracking)
 Combination reactions – combining two
molecules to make one or more products (like
reforming)
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Reaction type exercise
Determine the types of the reactions on the
following slide
Chemical equation exercise
CH4 + O2 = CO2 + H2O
 H2SO4 + NaOH = Na2SO4 + H2O
 CH3 SH + H2 = CH4 + H2S
 C6H6 + H2 = C6H14
 C7H16 = C3H6 + C4H8 + H2
 Fe + O2 = Fe2O3
 FeS + O2 = Fe2O3 + SO2
 Ca(OH)2 + H2SO4 = CaSO4 + H2O
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Reactions
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Reactions need time, temperature and
turbulence to take place effectively
Allow sufficient residence time
 Reactions go faster at higher temperatures
 Should provide good mixing
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Examples are catalytic cracking, reforming,
disinfection by chlorination, pH adjustment,
pulp production, combustion
Chemical bonding
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Bonding concerns how the outer electrons in the atomic shell
interact between two atoms to bind the two together
General classes of bonds are:
 Ionic – electrons are lost or gained
 Covalent – electrons are shared
Inorganic compounds generally have ionic bonds
Column 1 periodic table elements usually have a + 1 charge,
column 2 a +2 charge
Column 17 elements usually have a – charge and column 18
have a 0 charge
Organic compounds (carbon bonded to hydrogen) generally
have covalent bonds
Ionic compounds
Molecules have a neutral charge
 This means that the combination of positive
and negative ions in a molecule must balance,
i.e. for a O2- ion we will need two H+ ions to
balance the charge to make one molecule of
neutral water
 Practice charge balancing the following
reactions to make neutral products
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Chemical equation exercise
H+ + O -2 =
 H+ + (SO4) -2 =
 H+ + S -2 =
 Ca +2 + (OH) -1
 Fe+3 + O -2 =
 H+ + (PO4) -3 =
 Mg+2 + (SO4) -2 =
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Equilibrium
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Tendency of distribution or reaction in two directions
Example is liquid vapor equilibrium in a distillation tower ( a
species condensers from the vapor at the same rate as the
same species vaporizes from the liquid)
This is physical equilibrium
Chemical equilibrium concerns reactions
Reactants are in equilibrium with products
Example of equilibrium: CO2 + H2O ↔ H+ + HCO3- the rate
of reaction of carbon dioxide gas (CO2) with water is in
equilibrium with the rate of reaction of carbonate ion (HCO3) with H+ ion to form carbon dioxide gas
Law of mass action
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Law of mass action – adding more material to the left
side of the reaction shifts the reaction to the right
Example;
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HCO3- + Ca++ + HO- ↔ CaCO3 + H2O
Addition of base (HO-) will cause more of the calcium
(Ca++) and bicarbonate (HCO3- ) to precipitate as CaCO3
Phosphate (PO4-3) can be removed as precipitated
calcium phosphate by adding calcium oxide (CaO).
This is sometimes performed as tertiary treatment
to rid water of nutrients (phosphates)
Hydrogen ion concentration (pH)
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pH = log [1/(H+)] (where H+ concentration is in
moles per liter)
pH of neutral water is 7
pH rises as the solution becomes more alkaline or
basic
pH falls as the solution becomes more acidic
Can use a meter or pH paper to estimate pH
Restrictions on pH of discharged water
A fun website for pH is
http://www.miamisci.org/ph/phlemon.html
Coagulation
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Colloids and coagulation
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Colloids are very small particles that do not settle out (clay, organics,
microscopic organisms)
Some are attracted to water, some not
Chemical coagulation is used to remove colloids
Coagulation is the use of chemicals to destablize colloids so
that they can attract each other and settle
Coagulants include iron or aluminum sulfates
Flocculation is the process of attraction to form solids that
settle
Polymers are often used as flocculation aids
Coagulation and flocculation are followed by settling
Water constituents
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Organic compounds present in wastewater
Alcohols (-OH), aldehydes (=O), carboxylic acids
(-COOH), carbohydrates, fats, protein
 Biodegradable organic content in wastewater is
about 60 – 80%
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Inorganic ions and compounds present in
wastewater
Ions such as calcium, magnesium, phosphates,
nitrates, carbonates
 Gases such as hydrogen sulfide and oxygen
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