HYDROCARBON FUELS

1
HYDROCARBON FUELS

• MANY ARE ALKANES
• ALKANES ARE HYDROCARBONS CONTAINING ONLY SINGLE
  BONDS BETWEEN CARBONS

2

• OFTEN ARE MIXTURES OF STRAIGHT CHAIN AND BRANCHED
  CHAIN ALKANES

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HYDROCARBONS CONTINUED

• STRAIGHT CHAIN ALKANES ALKANES IN WHICH CARBONS
  ARE BONDED TO NO MORE THAN 2 OTHER CARBONS

4

• BRANCHED CHAIN ALKANES AT LEAST ONE CARBON IS
  BONDED TO 3 OR 4 OTHER CARBONS

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PREFIXES FOR ORGANIC COMPOUNDS

• METH
• ETH
• PROP
• BUT
• PENTA

• HEXA
• HEPTA
• OCTA
• NONA
• DECA

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STRAIGHT CHAIN ALKANE EXAMPLES

• CH4
• METHANE
• C2H6
• ETHANE

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• C3H8
• PROPANE

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MOLECULAR FORMULAS OF ALKANES

• GENERAL FORM IS CNH2N2 WHERE N IS THE NUMBER OF
  CARBONS

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STRUCTURAL FORMULAS OF SC ALKANES

• CONNECT CARBONS IN A STRAIGHT CHAIN WITH SINGLE
  BONDS

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• ATTACH HYDROGENS SO THAT EVERY CARBON HAS 4 BONDS
  IN TOTAL

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INTERMOLECULAR ATTRACTION FORCES

• CAUSED BY OPPOSITE CHARGES IN ATOMS
• AFFECTED BY UNEQUAL SHARING OF ELECTRONS IN
  COVALENT BONDS

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IM FORCES CONTINUED

• DETERMINE PHASE, MELTING POINT, BOILING POINT,
  DENSITY, AND VISCOSITY

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MELTING

• SOLIDS HAVE MOLECULES CLOSE TOGETHER IN RIGID
  POSITIONS
• TO MELT, MOLECULES MUST GAIN ENERGY AND MOVE
  APART SLIGHTLY

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MELTING CONTINUED

• THIS REQUIRES THEM TO OVERCOME ATTRACTION FORCES
• SUBSTANCES WITH STRONG ATTRACTION FORCES REQUIRE
  MORE ENERGY FOR THIS TO HAPPEN

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MELTING CONTINUED

• MORE ENERGY MEANS THEY HAVE HIGHER MELTING POINTS
  THAN SUBSTANCES WITH WEAKER ATTRACTION FORCES

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BOILING

• MOLECULES MUST GAIN ENERGY AND MOVE FARTHER APART
  IN ORDER TO BOIL

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• SUBSTANCES WITH STRONG ATTRACTION FORCES REQUIRE
  MORE ENERGY FOR THIS TO HAPPEN

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BOILING CONTINUED

• WHAT AFFECT DOES THIS HAVE ON THE BOILING POINT?

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VISCOSITY

• VISCOSITY IS THE RESISTANCE TO FLOWING
  (THICKNESS)
• HIGH VISCOSITY MEANS THICK (DOES NOT EASILY FLOW)

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• HIGH VISCOSITY IS THE RESULT OF STRONG ATTRACTION
  FORCES

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DENSITY

• HOW MUCH MASS IN A GIVEN SPACE
• RELATED TO CLOSENESS OF MOLECULES
• WHAT AFFECT DOES STRONG ATTRACTION FORCES HAVE?

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PROPERTY DIFFERENCES OF SC ALKANES

• AS THE MOLECULES GET LONGER, THEY ATTRACT ONE
  ANOTHER MORE
• LONGER IS STRONGER!

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PROPERTY DIFFERENCES

• WHAT HAPPENS TO MP?
• WHAT HAPPENS TO BP?
• WHAT HAPPENS TO VISCOSITY?
• WHAT HAPPENS TO DENSITY?

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ISOMERS

• COMPOUNDS HAVING THE SAME MOLECULAR FORMULA BUT
  DIFFERENT STRUCTURAL FORMULAS
• EXAMPLE BUTANE AND METHYLPROPANE

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ISOMERS CONTINUED

• METHANE, ETHANE, AND PROPANE HAVE NO ISOMERS
• ALL OTHER ALKANES HAVE AT LEAST ONE ISOMER

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• FUELS ARE OFTEN MIXTURES OF ISOMERS

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PROPERTY DIFFERENCES OF ISOMERS

• BRANCHING KEEPS THE MOLECULES FROM BEING AS CLOSE
  TOGETHER AS STRAIGHT MOLECULES
• THIS CAUSES WEAKER INTERMOLECULAR FORCES

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PROPERTY DIFFS CONTINUED

• HAVE DIFFERENT BOILING POINTS, MELTING POINTS,
  DENSITIES, AND VISCOSITIES THAN STRAIGHT CHAIN
  ISOMERS

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• MORE BRANCHING HAS A GREATER EFFECT

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EXAMPLE EFFECTS

• C5H12
• PENTANE BP IS 36.1 ?C
• 2 METHYL BUTANE BP IS 27.8 ?C
• 2 DIMETHYL PROPANE BP IS 9.5 ?C

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PROPERTY DIFFS CONTINUED

• WHAT EFFECT DOES BRANCHING HAVE ON MP?
• DENSITY?
• VISCOSITY?

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PETROLEUM

• ALSO CALLED CRUDE OIL
• LIQUID FOSSIL FUEL (MADE FROM DECOMPOSING ORGANIC
  MATTER)

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• MIXTURE OF HYDROCARBONS, NITROGEN, SULFUR,
  OXYGEN, AND SOME METAL COMPOUNDS

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DISTILLATION

• PROCESS OF SEPARATING LIQUIDS WITH DIFFERENT
  BOILING POINTS

35

• FRACTIONAL DISTILLATION SEPARATES MIXTURES INTO
  MANY PARTS BASED ON BP
• SEE PAGE 174

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DISTILLATION CONTINUED

• PRODUCTS ARE A MIXTURE OF VARIOUS HYDROCARBONS
• PETROCHEMICAL SUBSTANCE MADE FROM PETROLEUM

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CRACKING

• BREAKING LONG CHAIN MOLECULES INTO SHORTER ONES
  (C1 TO C14)

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• INVOLVES A CATALYST A SUBSTANCE THAT SPEEDS UP
  A REACTION W/O BEING CONSUMED ITSELF

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GASOLINE

• HEXANE, HEPTANE, AND OCTANE TOO BURN RAPIDLY AND
  CAUSE ENGINE KNOCK (IGNITING TOO SOON)

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• BRANCHED CHAIN ALKANES ARE BETTER FUELS SINCE
  THEY DONT KNOCK AS MUCH

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GASOLINE CONTINUED

• 2,2,4 TRIMETHYLPENTANE (AN ISOMER OF OCTANE) IS
  THE BEST FUEL FOR CAR ENGINES BECAUSE IT DOES NOT
  KNOCK AS MUCH

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• ALSO CALLED ISOOCTANE

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OCTANE NUMBER

• RATING SHOWING HOW A FUEL COMPARES TO THE
  CHARACTERISTICS OF ISOOCTANE
• HEPTANE ASSIGNED A RATING OF ZERO (IT IS A VERY
  POOR FUEL)

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OCTANE CONTINUED

• EXAMPLE 87 MEANS THE FUEL HAS THE SAME KNOCKING
  AS 87 ISOOCTANE AND 13 HEPTANE

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• 100 IS PURE ISOOCTANE (NOT THE HIGHEST NUMBER)

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FUEL ADDITIVES

• ADDED TO IMPROVE OCTANE RATING
• TETRAETHYL LEAD (C2H5)4Pb SLOWS THE BURNING OF
  ALKANES AND REDUCES KNOCK AND ADDED 3 POINTS TO
  THE OCTANE RATING

47
FUEL ADDITIVES CONT.

• LEAD BASED ADDITIVES NO LONGER USED DUE TO
  ENVIRONMENTAL POLLUTION

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OXYGENATED FUELS

• BLENDED WITH GAS TO ADD OXYGEN WHICH IMPROVES
  OCTANE RATING AND REDUCES CARBON MONOXIDE OZONE

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• EXAMPLES METHANOL, ETHANOL, AND MTBE (METHYL
  TERT BUTYL ETHER)

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OXYGENATED FUELS CONTINUED

• ARE VOCs
• ALSO CALLED REFORMULATED GASOLINE
• REQUIRED IN POLLUTED AREAS

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• MTBE HAS BEEN FOUND IN DRINKING WATER EFFECTS
  UNKNOWN

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CHEMICAL REACTIONS

• SUBSTANCES THAT GO INTO THE REACTION ARE CALLED
  REACTANTS
• SUBSTANCES MADE FROM THE REACTION ARE CALLED
  PRODUCTS

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CHEMICAL EQUATIONS

• DESCRIBE REACTIONS
• MUST BE BALANCED (NUMBERS OF ATOMS MUST BE THE
  SAME ON BOTH SIDES) BECAUSE OF THE LAW OF
  CONSERVATION OF MATTER

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CHEMICAL EQUATIONS CONTINUED

• COEFFICIENTS SHOW HOW MANY MOLECULES ARE
  INVOLVED IN A REACTION

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BALANCING EQUATION

• CHANGE COEFFICIENTS (NOT SUBSCRIPTS) SO THAT
  NUMBERS OF EACH ELEMENT ARE EQUAL ON BOTH SIDES

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EXAMPLE 1

• H2 O2 ? H2O
• 2H2 1O2 ? 2H2O

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EXAMPLE 2

• Na Cl2 ? NaCl
• 2Na 1Cl2 ? 2NaCl

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EXAMPLE 3

• CH4 O2 ? CO2 H2O
• 1CH4 2O2 ? 1CO2 2H2O

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COMBUSTION OF HYDROCARBONS

• RAPID EXOTHERMIC REACTION WITH OXYGEN
• ALSO CALLED BURNING
• PRODUCTS OF COMPLETE COMBUSTION ARE CO2 AND H2O

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EXAMPLE COMBUSTION REACTION FOR WAX

• 1C25H52 38O2 ? 25CO2 26H2O

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INCOMPLETE COMBUSTION

• CAUSED BY INSUFFICIENT OXYGEN
• PRODUCTS INCLUDE SOME CARBON MONOXIDE AND CARBON
  (SOOT)

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CATALYTIC CONVERTERS

• HIGH TEMPERATURE ENCOURAGES COMPLETE BURNING TO
  REDUCE CO AND CARBON EMISSIONS IN EXHAUST

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HEAT OF COMBUSTION

• THE ENERGY GIVEN OFF BY BURNING IS CALLED THE
  HEAT OF COMBUSTION
• AMOUNT OF HEAT VARIES WITH FUEL

64

• EXPRESSED IN KILOJOULES PER GRAM

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HEAT OF COMBUSTION CONTINUTED

• hC ENERGY PRODUCED / MASS BURNED
• METHANE IS 55. 6 kJ/g
• PROPANE IS 50.0 kJ/g
• BUTANE IS 49.3 kJ/g

66

• OCTANE IS 47. 8 kJ/g
• PREDICTION FOR DECANE?

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OXIDATION

• ANY REACTION IN WHICH A SUBSTANCE LOSES ELECTRONS
• IRON LOSES ELECTRONS TO OXYGEN DURING RUSTING

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REDUCTION

• ANY REACTION IN WHICH A SUBSTANCE GAINS ELECTRONS
• OXYGEN GAINS ELECTRONS FROM IRON DURING RUSTING

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EXAMPLE REACTION

• Zn O ? Zn2 O-2
• ZINC LOSES 2 ELECTRONS AND IS OXIDIZED
• OXYGEN GAINS 2 ELECTRONS AND IS REDUCED

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HALF REACTIONS

• SHOW THE OXIDATION OR REDUCTION SEPARATE FROM THE
  OTHER
• Zn ? Zn2 2e-
• O 2e- ? O-2

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OXIDATION-REDUCTION REACTION

• CALLED A REDOX REACTION
• ALSO CALLED A GALVANIC PROCESS

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OXIDATION CONTINUED

• MAKES ELECTRONS AVAILABLE
• THE RELEASED ELECTRONS FLOW TO FORM A CURRENT

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OXIDATION CONTINUED

• THE AMOUNT OF CURRENT IS RELATED TO HOW STRONGLY
  ATOMS HOLD VALENCE e-
• DIFFERENT FOR EACH ELEMENT

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OX CONTINUED

• ELECTRONS WILL FLOW FROM AN ELEMENT THAT GIVES
  THEM UP EASILY TO ONE THAT DOES NOT GIVE THEM UP
  EASILY
• THIS CAUSES AN ELECTRIC CURRENT

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POTENTIAL DIFFERENCE

• FORCE PUSHING ELECTRONS IN A CURRENT
• CALLED VOLTAGE

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GALVANIC CELL

• A DEVICE CONTAINING SUBSTANCES THAT UNDERGO AN
  REDOX REACTION AND PRODUCE A VOLTAGE

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• ALSO CALLED VOLTAIC CELL

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GALVANIC CELL CONTINUED

• SUBSTANCES ARE SEPARATED
• REACTION TAKES PLACE WHEN THE SUBSTANCES ARE
  CONNECTED WITH A CONDUCTOR

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PARTS OF A CELL

• CATHODE IS THE PLACE WHERE REDUCTION OCCURS
  (ELECTRONS FLOW TO IT)
• CATHODE IS POSITIVE

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PARTS OF A CELL CONT.

• ANODE IS THE PLACE WHERE OXIDATION OCCURS
  (ELECTRONS FLOW FROM IT)
• IT IS NEGATIVE

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• ELECTROLYTE SUBSTANCE THAT ALLOWS IONS TO MOVE
  IN THE CELL

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BATTERY

• A SERIES OF GALVANIC CELLS (SOME ARE ONLY 1 CELL)
• DRY CELLS USE MOIST ELECTROLYTES RATHER THAN
  LIQUID ONES

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CARBON DRY CELL

• GRAPHITE ROD SURROUNDED BY MOIST MnO2 CARBON
  PASTE IS THE CATHODE
• ZINC ANODE (CASE)
• MOIST NH4Cl AND ZnCl2 ELECTROLYTE

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DRY CELL CONTINUED

• Mn IS REDUCED
• REACTION PRODUCES AMMONIA GAS THAT CAUSES BATTERY
  TO EXPAND
• ELECTROLYTE IS ACIDIC

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ALKALINE DRY CELL

• CATHODE IS A MOIST PASTE OF MnO2 AND GRAPHITE
• ANODE IS MOIST PASTE OF ZINC AND KOH AROUND A
  BRASS COLLECTOR

86
ALKALINE VS. CARBON

• HAS LONGER SHELF LIFE THAN CARBON DRY CELL
• LESS ACIDIC
• NO AMMONIA GAS
• MORE RELIABLE OPERATING LIFE

87
LEAD STORAGE BATTERY

• ANODE IS LEAD METAL
• CATHODE IS PbO2
• ANODE IS OXIDIZED TO Pb2
• CATHODE IS REDUCED FROM Pb4 TO Pb2

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LEAD STORAGE CONTINUED

• Pb2 COMBINES WITH SO4-2 FROM SULFURIC ACID
  ELECTROLYTE TO FORM PbSO4

89

• APPLYING A VOLTAGE TO THIS BATTERY CAUSES PbSO4
  TO REACT WITH WATER TO FORM PbO2 AND Pb

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NICKEL-CADMIUM BATTERY

• ANODE IS CADMIUM
• CATHODE IS NiO2
• ELECTROLYTE IS KOH SOLUTION

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CORROSION

• A NATURAL GALVANIC PROCESS (REDOX REACTION)
• OCCURS WHEREVER ACTIVE METALS ARE IN CONTACT WITH
  SUBSTANCES THAT CAN OXIDIZE THEM

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RUST

• OXIDATION OF IRON BY OXYGEN IN THE PRESENCE OF
  WATER
• WATER IS THE ELECTROLYTE
• ANODIC RXN Fe ? Fe2 2e-

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• MANY CATHODIC REACTIONS

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RUST CONTINUED

• OVERALL 2Fe 3O2 ? 2Fe2O3

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CORROSION INHIBITORS

• SUBSTANCES THAT SLOW THE RATE OF ELECTRON
  TRANSFER FROM THE OXIDIZED SUBSTANCE
• ADDED TO CAR COOLING SYSTEM STICK TO IRON
  SURFACE

96
INHIBITORS CONTINUED

• EXAMPLES CERTAIN PHOSPHATES, CHROMATES, AND
  ORGANIC COMPOUNDS
• PAINT CONTAINING RED LEAD (Pb3O4) OR ZINC
  CHROMATE (ZnCrO4) WORK WELL

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CATHODIC PROTECTION

• PUT A MORE ACTIVE METAL IN CONTACT WITH METAL TO
  BE PROTECTED
• ZINC OR MAGNESIUM IS OFTEN USED

98

• THEY OXIDIZE INSTEAD OF THE PROTECTED METAL

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GALVANIZED IRON

• COATED WITH A ZINC COMPOUND TO PROVIDE CATHODIC
  PROTECTION