chemistry p3 IGCSE !! (some important points)

[dana xP]

hey there thought to share some points about chemstry since the exam is approaching in wednesday !!
i would start with organic chemistry first then later i would post the rest !!
1-hydrocarbons are composed of hydrogen and carbon
2-the general formulas r:
ALKANES = CnH2n+2
ALKENES = CnH2n
ALKOHOLS= CnH2n+1OH
ACIDS = CnH2n+1COOH
3-ALKANES burn with a blue-yellow flame
ALKENES burn with a smoky yellow flame
4-to diffrenciate between alkanes and alkenes:
test : add aq.bromine
result : with alkenes red brown colour changes to colorless
5- chloroethane = ethane+Cl2 OR ethene+HCl
dichloroethene = ethene+Cl2
6-polyethene is used in making plastic bags and sheets !!
7-plastics r used as insulators since they doesnt conduct electricity
8- OH group is also called hydroxyl or hydroxide group
9-the suitable temperature for yeast to work is 35*C
10-yeast dies after fermentation due to :
-due to alkohol poisoning
-the reactants might have been used up
11-biotechnology is using of microorganisms to make food
12-properities of ethanol and methanol :
ethanol= *sweet smelling
*colourless liquid
*has a boiling point of 78*C
methanol=*volatile liquid
*highly toxic
12-narural sources of methane
*natural gas
*the decay of dead plants
13-sources of sulphur are fossil fuels

hope that it would be helpful to all of u guys !!
study well and inshallah u will get A*
(btw if u have got extra points or important ones ,,,, or simplified notes ,,,,, plz post it here it would help a lot of people (iam one of them) ) and thanx !!

 

[dana xP]

any help for the lesson air and water ??

 

[Penalopi]

any help for the lesson air and water ??

You need to know:
-The chemical and physical test for water
-The purification of water- sedimentaion, filtration and chlorination
-All about air polltuion:
=Carbon monoxide: produced as a result of incomplete burning and causes the formation of carboxyhaemoglobin in the human body.
= Sulphur dioxide: Produced by burning fossil fuels and causes acid rain
= Nitrogen oxides: Produced by car engines and causes acid rain and destroys the Ozone layer
= Lead Volatile compounds: Produced by the burning of lead compounds and they r toxic to the CNS
-Preparation of oxygen in the lab (decomposition of H2O2 ) and in industry (by fractional distillation of liquid air)
-Chemical properties and test for oxygen (relights glowing splint)
-Uses of oxygen (In hospitals, in oxyacetylene welding, in oxygen furnace....e.t.c.)
- Production of ammonia by Haber proccess:
N2 + 3 H2 <-----> 2NH3 (temp: 450 , Pressure: 200- 250, with catalyst iron fillings)

Hope that helped

 

[dana xP]

You need to know:
-The chemical and physical test for water
-The purification of water- sedimentaion, filtration and chlorination
-All about air polltuion:
=Carbon monoxide: produced as a result of incomplete burning and causes the formation of carboxyhaemoglobin in the human body.
= Sulphur dioxide: Produced by burning fossil fuels and causes acid rain
= Nitrogen oxides: Produced by car engines and causes acid rain and destroys the Ozone layer
= Lead Volatile compounds: Produced by the burning of lead compounds and they r toxic to the CNS
-Preparation of oxygen in the lab (decomposition of H2O2 ) and in industry (by fractional distillation of liquid air)
-Chemical properties and test for oxygen (relights glowing splint)
-Uses of oxygen (In hospitals, in oxyacetylene welding, in oxygen furnace....e.t.c.)
- Production of ammonia by Haber proccess:
N2 + 3 H2 <-----> 2NH3 (temp: 450 , Pressure: 200- 250, with catalyst iron fillings)

Hope that helped

yeah thanks alot sis !! helped me a great deal !!

 

[nehaloo]

nice.. good work

 

[dana xP]

nice.. good work

thanx if u also have any points plz post them as it may help many other people (including me) !!

 

[nehaloo]

ok sure i'll isa

 

[dana xP]

now important points for the lesson electricity and chemistry !!
1-u should know all definitions (conductors , non-conductors , semi-conductors , electrolytes , non-electrolytes , electrolysis , inert electrodes , active electrodes ) with examples !!
2-for chemical changes that takes place at the electrodes:
*electrons flow through the external circuit
*convectional current moves in the opposite direction of the electrons flow
*ions moves through the solution
3-for the observation at the electrodes , u should memorise the following :
-for gases
*Cl2 = green gas
*O2 = colourless (bubbles can be seen)
*Br2 = red brown gas
*I2 = purple gas
-for metals
*Cu = red brown deposite
*all group I metal = grey metal deposite
4-electrolyte has 3 forms :
*acid + water
or
*molten ionic compound
or
*aqueous solution (sallt + water)
5-learn the diagrams for the electrolysis of:
-brine (NaCl)
-HCl
-bauxite (Al2O3)
6-aqueous solutions contain OH' ion,,, which when chosen gives
4OH' = O2 + 2H2O + 4e'
7-the blue colour of the solution fades away ,,,, since the copper ion from the solution moves to the cathode and deposit there as copper ions
8-in electroplating :
*cathode is rotated for uniform coating
*clean the metal to be coated so that the other metal can stick on it properly

hope that it was helpful ,,,, and if it was plz pray for me to get an A* !!

 

[areebaization]

TY guys that was really helpful! BTW what do we need to know in the basic O2 furnace? The whole story?

 

[Penalopi]

yeah thanks alot sis !! helped me a great deal !!

ur welcome

 

[Penalopi]

TY guys that was really helpful! BTW what do we need to know in the basic O2 furnace? The whole story?

All you need to know is that oxygen is blown into the furnace (which is full of pig iron) so it reacts with the carbon (impurity) producing CO2... Oxygen is blown into the furnace until only 1% carbon remains.

 

[dana xP]

TY guys that was really helpful! BTW what do we need to know in the basic O2 furnace? The whole story?

-in this furnace haematite (iron core) is changed in to iron by using O2 + C (COKE) +CaCO3
-in the furnace 5 steps takes place
*C + O2 = CO2
*CO2 + C = 2CO
*3CO + Fe2O3 = 2Fe + 3CO2
*CaCO3 = CaO + CO2
*CaO + SiO2 = CaSiO3 (slag)
-this slag floats over IRON , which protects it from further oxidation .

hope that it was useful to u !!

 

[areebaization]

-in this furnace haematite (iron core) is changed in to iron by using O2 + C (COKE) +CaCO3
-in the furnace 5 steps takes place
*C + O2 = CO2
*CO2 + C = 2CO
*3CO + Fe2O3 = 2Fe + 3CO2
*CaCO3 = CaO + CO2
*CaO + SiO2 = CaSiO3 (slag)
-this slag floats over IRON , which protects it from further oxidation .

hope that it was useful to u !!

Isn't this the blast furnace? :S

 

[areebaization]

-in this furnace haematite (iron core) is changed in to iron by using O2 + C (COKE) +CaCO3
-in the furnace 5 steps takes place
*C + O2 = CO2
*CO2 + C = 2CO
*3CO + Fe2O3 = 2Fe + 3CO2
*CaCO3 = CaO + CO2
*CaO + SiO2 = CaSiO3 (slag)
-this slag floats over IRON , which protects it from further oxidation .

hope that it was useful to u !!

and BTW yeah it sure is useful to me
I love how precise u're! Great teacher

 

[dana xP]

Isn't this the blast furnace? :S

well then ,,, isnt this what u asked for??!!

 

[dana xP]

and BTW yeah it sure is useful to me
I love how precise u're! Great teacher

thanx !!

 

[areebaization]

well then ,,, isnt this what u asked for??!!

I needed it though..but I asked about basic O2 furnace, found it now Thanx a bunch!

 

[dana xP]

I needed it though..but I asked about basic O2 furnace, found it now Thanx a bunch!

oh i see ok ,,,,no problem,,,,,ur welcome !!
and if u have anything about chemistry p3 ,,,plz share it with us

 

[areebaization]

oh i see ok ,,,,no problem,,,,,ur welcome !!
and if u have anything about chemistry p3 ,,,plz share it with us

Guys I didnt want to post this cause I thought It wouldn't be of much help as it is endorsed by CIE themselves...Anyway, now am posting this, just incase anybody missed it on their site. Tips relate to June 2004
paper.
Acids and bases
• Don’t confuse the pH scale with the degree of acidity. The more acidic the substance, the
lower the pH – learn this by remembering that ‘a’ (for acid) is the lowest numbered letter of
the alphabet (1.30)
• A common error is to think that less sodium hydroxide is needed to neutralise a weak acid
than to neutralise a strong acid of the same concentration. The same amount is needed
because the hydroxide is reacting with all the acidic hydrogens in the molecule, not just those
that have ionised (3.6(b)(ii))
• The phrase ‘explain why this acid is acting as a base’ demands a chemical reason (usually
based on particle theory). The examiner is looking for an answer involving proton transfer.
Vague answers (such as ‘it is neutralising the base’) are not accepted as they do not give an
explanation (3.2(b)(iv))
• Simple inorganic salts such as sodium chloride are generally neutral when dissolved in water
– they are not acidic (1.3)
• Nitric acid is a strong, not a weak, acid (6.7(c))
Air and water
• To remember that carbon monoxide is poisonous (it binds to haemoglobin), think of the ‘nox’
in carbon monoxide as being short for noxious (poisonous). The effects of pollutant gases on
nature are often confused, as not all pollutant gases are acidic. Know the different effects of
carbon monoxide, sulphur dioxide and carbon dioxide (1.31)
• A common error is to think that fume cupboards keep air away from a reaction. Fume
cupboards have a continuous airflow to allow poisonous vapours to escape through the fan
(6.3(d))

 

[areebaization]

Atomic structure and bonding
• It is a common mistake to count the bonds and not the electrons when asked about the
number of electrons shared between the atoms in a molecule. For example, the number of
shared electrons in methane is eight not four (1.8)
• Take care when writing electronic structures including hydrogen. Always show the hydrogen
atom either as a circle or (if ionic) by its symbol. It is best practice to write the symbol of the
atom in the centre so it is clear to the examiner which atom is which (2.1(f)(i))
• When writing dot-and-cross diagrams for ionic structures, put the charge outside of the
brackets, at the top, not in the centre of the atom
• When asked about the number of covalent bonds in a compound, focus on the outer energy
level / shell electrons that are shared, not the total number of electrons. Remember that some
molecules have non-bonding pairs of electrons e.g. nitrogen (3.1(b)(i)) • When drawing dot-and-cross diagrams for molecules such as nitrogen which have only three
bonding pairs of electrons, don’t forget to draw in the lone pairs of electrons. Remember that
there must be eight electrons surrounding each atom (3.3(b))
• Practice drawing diagrams of giant molecule structures, including silicon dioxide, diamond
and graphite, as these are nearly always drawn badly. You must show the continuation bonds
(3.1(c)(i))
Electrochemistry
• A common mistake is to think that sulphate ions break up during the electrolysis of aqueous
solutions into sulphur dioxide. In fact, oxygen is given off at the positive electrode (from the
electrolysis of the water) (3.5(b)(ii))
• If the exam paper shows an electrical circuit to test conduction, observations can also include
what can be seen to be happening in the circuit e.g. ‘the bulb lights up’ (6.3(a))
Energy changes
• If asked whether a reaction is endothermic or exothermic, remember the following:
endothermic – heat is put in (e.g. you have to heat with a Bunsen to get a reaction);
exothermic – heat is given out (e.g. burning fuels and neutralisation reactions are always
exothermic) (1.18)