CHEM - THINGS TO RECITE
isotopes
- atoms of an element which have the same number of protons but different number of
neutron
allotropes
- different forms of the same element
Fossil Fuel
- fuels form from dead remains of living(coal : land // marine : petroleum and natural
gas) organism that lives millions of years ago
Cracking
- process where larger molecules are break down into smaller molecules by heat with the help
of a catalyst
Structural Isomers
- same molecular formula different structural formula (chain // position // functional
group)
Chain Isomers
- same functional groups , different carbon skeleton
Position Isomers
- same functional group , different position of them
Functional Group Isomers
- different functional group
Stereoisomerism
- atoms linked in the same way but differ in spatial arrangement of atoms
Enantiomers
- cause same extent of rotation of plane of plane-polarized light in opposite direction ,
using a polarimeter
Disadvantages of track progress with titration
- difficult to monitor change in concentration continuously
- cannot be used to study fast reaction as titrimetric analysis takes time
Filter
- select light then coloured species absorb the most
Catalyst
- substance that changes the rate of reaction while itself remains chemically unchanged
Avogadro’s law
- equal volume of all gasses contain equal number of gas molecules
Characteristics of Chemical Equilibrium
1. dynamic in nature , the forward and backward reaction do not stop when the
equilibrium is reached
2. forward reaction rate equal to backward reaction rate and is not zero
3. exists only in a close system
4. can be reached from either forward or backward direction
Periodicity
- repeating pattern of physical and chemical properties shown by different periods
Properties of Transitional Metals
1. coloured compounds : iron (II) chloride // iron (III) chloride
2. existence of more than one oxidation state in compound : +2 // +3
3. catalytic properties of metal and compound : haber process // Decomposition of
hydrogen peroxide
Hess Law
- the total enthalpy change of a chemical reaction is independent of the route by which
the reaction takes place
Why enthalpy change cannot be found directly
1. formation of side product (carbon dioxide from formation of carbon monoxide)
2. reaction rate to slow (rust)
3. too dangerous to be performed in lab (potassium to acid)
4. extent of reaction cannot be controlled
5. direct combustion is vigorous
Enthalpy change
- heat change at constant pressure
Standard Enthalpy change of combustion
- the enthalpy change of complete combustion of one mole of the substance in oxygen
under standard conditions
Below, you will find an overview (non-exhaustive!) of all reactions in the HKDSE
Chemistry syllabus, DO NOT rely only on the following list, it serves only to give you a
general sense and final reminders.
Metal extraction
1. Metal ores → metal + O2 (direct heating)
2. Metal ores + C → metal + CO2 (carbon reduction)
Metal reactions
1. Metal + O2 → metal oxide
2. Metal + water → metal hydroxide + H2
3. Metal + steam → metal oxide + H2
4. Metal + acid → salt + H2 (not water)
5. 4Fe(s) + 3O₂(g) + 2nH₂O(l) → 2Fe₂O₃ . nH₂O(s) (rusting)
Acid reactions
1. Dilute acid + metal → salt + H2
2. Acid + base → salt + water (neutralisation)
3. Acid + CO3 2- → salt + water + CO2
4. Acid + HCO3- → salt + water + CO2
5. Acid + SO3 2- → salt + water + SO2
6. Acid + HSO3- → salt + water + SO2
Base reactions
1. Base + ammonium salt → salt + water + NH3
2. Base + acid → salt + water (neutralisation)
Alkanes
1. Fuel + O2 → CO2 + H2O (complete combustion)
a. Toxic CO is produced under incomplete combustion
2. Alkane + Cl2/Br2 → haloalkane (substitution)
a. To differentiate alkane vs alkene
i. Alkane: bromine under UV light
ii.
Alkene: bromine in the dark
3. Large alkane → small alkane + small alkene (cracking)
a. Heat in absence of oxygen under high pressure / catalyst
Alkenes
1. Alkene + Cl2/Br2 → haloalkane (addition)
2. Alkene → alcohol (addition)
a. With cold alkaline dilute KMnO4
i. Just recite it, I don't know why its cold alkaline too =)
3. Alkene → polymer (addition polymerisation)
Redox
You must refer to your own notes for redox and you must be able to
1. Recite all common OA RA by heart
2. Know their colour changes
3. Know how to find ON
4. Know how to write and balance redox equation
5. Recite the two chemical cells by heart
Section below is dedicated to reactions (conversions) of carbon compounds
Alkane
1. Alkane + Cl2/Br2 → haloalkane
Alkene
1. Alkene + H2 → Alkane
a. Pt / Ni with heat
2. Alkene + Cl2/Br2 → haloalkane
3. Alkene + HX → haloalkane
4. Alkene → alkanol (diol)
a. Cold alkaline KMnO4
Haloalkane RX
1. RX + OH- → ROH (alcohol)
Alcohol ROH
1. ROH + HX / PX3 → haloalkane
2. ROH → alkene (dehydration)
a. Conc H2SO4 / Al2O3 with heat
3. Primary ROH → aldehyde (oxidation)
a. Acidified Cr2O7 / MnO44. Secondary ROH → ketone (oxidation)
a. Acidified Cr2O7 / MnO4-
Aldehyde
1. Aldehyde → RCOOH (carboxylic acid) need to lerant spelling!
a. Acidified Cr2O7 / MnO4-, heat under reflux
2. Aldehyde / Ketone → alcohol
a. 1)LiAlH4 in dry ether 2) H+ / NaBH4
RCOOH
1. RCOOH + ROH → ester + water (esterification)
a. Conc H2SO4, heat
2. RCOOH → primary ROH
a. 1)LiAlH4 in dry ether 2) H+ / NaBH4
3. RCOOH + NH3 → amide
a. Heat dont forget about this reaction!
Ester
1. Ester → RCOOH + ROH (acid hydrolysis)
a. H+, heat
2. Ester → R-COO- + R-OH (alkaline hydrolysis)
a. OH-, heat
Amide
1. Amide → RCOOH + NH4+ (acid hydrolysis)
a. H+, heat
2. Amide → RCOO- + NH3 (alkaline hydrolysis)
a. OH-, heat
Refers to the conversion diaphragm for details in 24 hours chemistry book
Questions types / topics that MUST appear in your HKDSE exam
1. Reactions related to metals
2. Reactions related to acid and base
3. Chemical cell & electrolysis setup
4. Mole calculation
5. Solubility
6. Titration procedures and calculation
7. Rate of change & equilibrium
8. Fossil fuels