Download Unit 2: Nature`s Chemistry

Unit 2: Nature’s Chemistry
1. A Fuel is a substance which burns giving out energy.
2. Oxygen is needed for anything to burn
3. Combustion is another name for burning
Test for Oxygen - Relights a glowing splint
Test for Carbon Dioxide – turns limewater milky
4.
Formation of Fossil Fuels (coal, oil, gas)
Coal: is formed from the remains of dead plants and trees.
Layers of sediment fall on top of these, over millions of
years coal forms.
Oil and Gas: formed from dead Sea creatures and plants.
FOSSIL FUELS ARE FINITE RESOURCES
5. Fractional Distillation of Crude Oil
Crude oil is a mixture of many different substances – needs to be
separated. It is separated into FRACTIONS by evaporation & condensing.
A Fraction is a group of similar sized molecules which have
similar boiling points
6.Differences between the fractions
COLOUR
FLAMMABILITY
Low Boiling
Fraction
High Boiling
Fraction
Gets
Darker
Less
Flammable
7. Fractions obtained in industry
Low
GASES
GASOLINE (PETROL)
NAPHTHA
KEROSINE (PARRAFIN)
DIESEL
RESIDUE
High
EASE
OF
EVAPOURATION
Harder to
Evaporate
VISCOSITY
More Viscous
(thicker)
USES
COOKING, HEATING
CARS
LIGHTING, HEATING
TRAINS, LORRIES
BITUMEN FOR TAR ON
ROADS
8. Burning Hydrocarbons
**HYDROCARBON + OXYGEN  CARBON DIOXIDE + WATER**
9. Pollution from burning fuels
CARBON MONOXIDE – Formed in limited air  POISONOUS
OXIDES OF NITROGEN – formed in car exhaust  ACID RAIN
SULPHUR DIOXIDE – formed due to sulphur impurities in certain fuels
 ACID RAIN
UNBURNT HYDROCARBONS
*** PREVENTION: Catalytic Converter (platinum) converts harmful gases
into un-harmful gases.
10. Hydrocarbons are compounds formed between HYDROGEN and
CARBON.
HYDROCARBONS
ALKANES
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
CnH2n+2
- contain only
C-C single
bonds
ALKENES
Ethene
Propene
Butene
Pentene
Hexene
Heptene
Octene
C2H4
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
CnH2n
- contain C=C
double bonds
UNSATURATED
SATURATED
CYCLOALKANES
Cyclopropane
Cyclobutane
Cyclopentane
Cyclohexane
Cycloheptane
Cyclooctane
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
CnH2n
- All C’s joined in a
circle
SATURATED
11.TEST FOR UNSATURATION ( C= C )
-UNSATURATED hydrocarbons rapidly decolourise
bromine solution
12. Full  Shortened Structural Formula
e.g.
H
H
H
H
H
C
C
C
C
H
H
H
H
H
CH3CH2CH2CH3
FULL STRUCTURAL FORMULA
C4H10
SHORTENED
STRUCTURAL FORMULA
MOLECULAR FORMULA
13.Homologous Series
Alkanes, alkenes, and cycloalkanes are examples of HOMOLOGOUS
SERIES.
In a homologous series:
(a)
members represented by GENERAL FORMULA
(b)
as the molecules get bigger, the melting and boiling points
increase
(c)
members have similar chemical properties
14.
Isomers – compounds which have same formula but different
structure
e.g.
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
H
H
C
C
C
H
H
H
C
H
H
H
Isomers have different properties eg. different melting and boiling
points.
15.Naming Branched Alkanes
- name longest carbon chain -> hexane
- number longest carbon chain to give lowest numbers to carbons with
branches attached
- name branches
-CH3 methyl
-CH2CH3 ethyl
-if more than one of same branch use prefix
di ( if two )
tri ( if three )
- name branched alkane
2,3-dimethylhexane
16.Naming Branched Alkenes
-
find longest carbon chain containing double bond
number this carbon chain to give lowest number to where double
bond starts -> pent-2-ene
indentify branches and indicate position with number in front of
branch name
4-methylpent-2-ene
17.Addition Reactions
Alkenes undergo ADDITION REACTIONS with hydrogen, halogens,
and water
e.g.
H
H
C
C
H
H
+ Br2
Br
H
H
C
C
H
H
Br
18.Cracking
Breaking long chain molecules into smaller, more useful molecules.
+
Catalyst needed (aluminium oxide)
e.g.
C10H22 C2H4 + C8H18
Cracking produces a mixture of UNSATURATED and SATURATED
molecules.
19. Alcohols ( alkanols )
contain -OH functional group
(called HYDROXYL GROUP )
+
ethanol
Alcohols are used as SOLVENTS and FUELS.
20. Carboxylic Acids ( alkanoic acids )
- contain CARBOXYL group
eg.
Vinegar is a solution of ethanoic acid. It is used as a food preservative
and in household cleaning products.
21. Esters
Esters are formed when a CARBOXYLIC ACID reacts with an
ALCOHOL.
This is a CONDENSATION reaction.
Some uses
PERFUMES.
of
esters
include
FLAVOURINGS,
SOLVENTS,
and
these are compounds containing CARBON,
OXYGEN
plants are a source of carbohydrates
carbohydrates are used as food or fuels
HYDROGEN,
and
22. Carbohydrates
-
Carbohydrates are grouped according to their size:
MONOSACCHARIDES C6H12O6
e.g. glucose, fructose
DISACCHARIDES C12H22O11
e.g. sucrose, maltose
POLYSACCHARIDES
(C6H10O5)n
e.g. starch
Testing for starch: turns Iodine Blue/ Black
Benedict’s Test: Turns blue  orange/ brown with
all sugars ending in ‘OSE’ except SUCROSE
Condensation Polymerisation
Starch is formed by joining many glucose molecules together:
3 Glucose Monomers
H 2O
Part of Starch Polymer
HYDROLYSIS
Breaking down large molecules into smaller ones using water.
e.g.
Starch + Water  Glucose
(C6H10O5)n + H2O  nC6H12O6
Alcohol
- produced by FERMENTATION of glucose
- YEAST (contains enzymes) is needed
- Ethanol is the alcohol formed
Glucose
Yeast
Ethanol + Carbon dioxide
Increasing the alcohol content
- by DISTILLATION (evaporate and condense)
- can only get ~15% alcohol by fermentation (alcohol kills enzymes in
yeast)
- ethanol boils at 79oC, water boils at 100oC
23. Calculations from Balanced Equations
-allows us to work out the mass of a product formed when the mass of
reactant is known
eg. Calculate the mass of MgSO4 produced when 4.9g of magnesium
reacts with excess sulphuric acid
Mg +
1mol
24.5g
H2SO4
1g
4.9g
MgSO4
1mol
120.5g
+
H2
MgSO 4
120.5g
24.5
120.5 x 4.9 g
24.5
= 24.1g
24. Energy from Fuels
Alkanes and alcohols can be used as fuels since they burn well.
Combustion is an EXOTHERMIC reaction.
In an exothermic reaction the products have less energy than the
reactants.
The amount of energy released by a fuel when it burns can be worked
out using:
Eh = cm∆T
c = 4.18 (specific heat capacity of water)
m = mass of water (in kg)
∆T= change in temperature (oC)