Spring, 2012Session 3 – General Chemistry Pt

1

Definition of terms Chemical formulas Chemistry background Reactions Equilibrium and law of mass action pH and acid base reactions Coagulation Water constituents

Inorganic chemistry Organic chemistry Atomic structure – protons, neutrons,

electrons Atoms and molecules Elements and compounds

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

· CO · CaO · C2H2

· CH4 · Ca(OH) 2 · C2H4

· CO2 · SO2 · C2H6

· H2O · N2 · H3 (PO)4

· HNO3 · MgO · ZnO

· H2SO4 · HF · P2O5

· NaOH · CaCO3 · H2S

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

For the reactions on the following slide explain:

what the reactants and products are what the ratio these molecules are inBalance the following equations so

that there is the same number of atoms of a species in the products as there is in the reactants

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

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

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/

A nice website with a lot of interactive information on chemistry is http://serendip.brynmawr.edu/sci_edu/chemsites.html

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.)

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

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)

Determine the types of the reactions on the following slide

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

Reactions need time, temperature and turbulence to take place effectively Allow sufficient residence time Reactions go faster at higher temperatures Should provide good mixing

Examples are catalytic cracking, reforming, disinfection by chlorination, pH adjustment, pulp production, combustion

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

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

H+ + O -2 = H+ + (SO4) -2 =

H+ + S -2 = Ca +2 + (OH) -1 Fe+3 + O -2 = H+ + (PO4) -3 =

Mg+2 + (SO4) -2 =

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 – adding more material to the left side of the reaction shifts the reaction to the right

Example; 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)

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

Colloids and coagulation 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

Organic compounds present in wastewater Alcohols (-OH), aldehydes (=O), carboxylic

acids (-COOH), carbohydrates, fats, protein Biodegradable organic content in wastewater

is about 60 – 80% Inorganic ions and compounds present in

wastewater Ions such as calcium, magnesium, phosphates,

nitrates, carbonates Gases such as hydrogen sulfide and oxygen