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CHEMISTRY |
GCSE Year 2010 Exams Target
Dr
Hector Perera
B.Sc (Hons) M.Sc Ph.D. Chemistry
EXCERPTS
Periodic table Updated
05 September 2009
In every GCSE examination,
there must be questions on the periodic table. In the book I have given some
model questions and answers on the Periodic table, which are likely to come up
in the examinations, one of them is as follows.
Question: 1a) Fill in the blanks with suitable words:
Vertical, transition, Groups, horizontal, halogens, periods, eight, zero, atomic numbers, alkali, alkali earth,
When the elements in the periodic
table are arranged in the increasing order of -----------, they fall into
-------- rows called ------- and -------rows called --------- There are eight
Groups and the -------- group is also called the Group ------- The middle block
of elements in the periodic table are the -------- elements and sometimes
called d block elements. Group one is the --------metals, Group two are the
---------- -------- metals, Group seven are the ---------.
Answer 1) a) When the
elements in the periodic table are arranged in the increasing order of atomic
numbers, they fall into-vertical rows called groups and horizontal
-rows called periods. There are eight Groups and the eight group
is also called the Group zero. The middle block of elements in the
periodic table are the transition elements and sometimes called d block
elements. Groups one are the alkali metals, Group two are the alkali
earth metals, Group seven are the halogens.
Moles
The questions are likely
to come up about moles in solids, liquids and gases. All these are addressed in
the book, under separate topics, with possible questions and detailed answers.
I have chosen very carefully, the type of question in each kind of moles and
explained it in detail with supplemented notes, for example.
[The number in front of the question and the answer is as found in the book. More questions about moles are found in page, 1, 3, 15, 45, 48, 51, 52, 73, 84]
Moles of solids and gases
CaCO3(s) + 2HCl(aq)---- 
CaCl2(aq)
+ CO2(g) + H2O(l)
The above reaction
shows, one mole of calcium carbonate [marble chips] reacts with two moles of
HCl to give one mole of carbon dioxide. One mole of carbon dioxide by weight is
44g, 24dm3by volume at [R.T.P] room temperature and pressure.
Question 2) b) How many moles of calcium carbonate are there in 5.0g of CaCO3(s).
Question 2) c) How many moles of carbon dioxide gas at R.T.P would be given out from 5.0g of calcium carbonate.
Answer 2) b) and the method:
Number of moles =
Mass/Relative molar mass.
,, ,, = 5/100
Hence the number of
moles = 0.05.
Note: Mass is 5.0g,
relative molar mass [the formula mass] = 100
Answer
2) c)
CaCO3(s) +
2HCl(aq)---- CaCl2(aq) + CO2(g) + H2O(l)
From the above
equation, 44g by weight or 24000cm3 by volume of carbon dioxide
would be obtained from 100g of calcium carbonate or from one mole of calcium
carbonate. 44g is the weight of one mole of CO2(g).
100g of CaCO3
gives out 44g of CO2 or 24000cm3 of CO2 at
R.T.P
5.0g of CaCO3 gives out 2.2g of CO2 or 1200cm3 of
CO2 at R.T.P
24000cm3 of CO2 is one mole [by volume]
1200 cm3 is 0.5moles of CO2
Ores of iron & reduction
Under extraction of metals,
I have explained the extraction of iron and aluminium and purification of
copper. The questions I have explained are the most likely ones to be asked and
I have explained the answers in the simplest ways.
Note the labelling of blast furnace, given on pages 23 and 24. Some
part questions about iron and related compounds are as follows, [The numbers in
front of the questions and answers are as found in the book]
Question 4a) What is meant by the term, an ore of iron is Heamatite?
Question 4b) What are the ores of iron?
Question
4c) Explain how iron is obtained from iron (3) oxide, write an equation to show
the reaction, name the type of the reaction.
This underlined part has gone to somewhere but it should be with Question 4c)
as shown above.
Answer 4a) This is a naturally occurring substance from which iron is
extracted.
Answer
4b) Ores of iron:
Haematite Fe2O3 , Magnetite Fe3O4,
Iron pyrite FeS2
Answer
4c) Iron (3) oxide is reduced with carbon monoxide to obtain iron, the type of
reaction is a reduction.
Fe2O3(s) + 3CO(g) ----- 2Fe(s) + 3CO2(g)
For GCSE purpose one has
to know the 1st twenty elements. I have
given the electron configurations and atomic structures of a few elements and
given helpful ideas to draw the others. [The numbers in front of the questions
and answers are as found in the book]
Question 6)
1. What is an element; give examples of elements from three different states.
2. Draw and label a hydrogen atom.
3. What is in the nucleus of a sodium atom, 23Na11
4. An element has 17 electrons, 18 neutrons and 17 protons, what is the atomic weight of the element.
Answers 6a) An element is a pure substance containing one kind of atoms only. Hydrogen, Oxygen and Helium are gaseous elements, Mercury is the only liquid element and Magnesium, Copper and Gold are examples of solid elements.
Answer 6b) The structure of a hydrogen atom.
I have given two structures of Hydrogen atom, the second one with more details.
Answer 6c) In the nucleus there are 11 protons and 12 neutrons.
Answer 6d) The atomic weight is 35 that is due to the number of protons and neutrons in an atom. Although the electrons are present in an atom, the weights of electrons are not taken for atomic weight because they are weightless compared to the weight of protons and neutrons.
Organic Chemistry
In any GCSE Exam, Organic
Chemistry is a must, the questions are very straightforward but some students
still get them wrong. I have asked simple question like, 'what is a
hydrocarbon, give two examples from everyday life' and some students couldn't
give the proper answers. Cooking gas is a hydrocarbon. All polythene bags are
nothing but hydrocarbons because they contain carbon and hydrogen only. A large
area of this book covers Organic Chemistry exclusively from the exam point of
view. I have given some examples below. It is always advisable to read exam
relevant questions and answers, as shown in the work I have covered. [The
numbers in front are the same found in the book]
Question 6) c) What is PVC, draw the structure?
Question 6) d): What are the uses of PVC?
Answer 6)a): Ethene, polymerisation. Polythene.
Answer 6) b)
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Ethene |
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Note: You must show the repeated unit inside the bracket with a ‘n’ which is a very large number. The bond coming out of the bracket joins with the next repeated unit, this must be drawn in exams. The catalyst must be mentioned, as Pt or Ni or as Ziegler Catalyst. {Ziegler is a name of a Nobel Prize winner who found the catalyst and to honour him, we now call it ‘ZIEGLER CATALYST’. In exams just write Ziegler catalyst, as the name of the catalyst.
Answer 6)c and the method)
Draw the structure of ethene and remove one H atom and replace it by Cl, then you get vinyl chloride, polymerise it to get PVC or polyvinyl chloride. Find it difficult?
The non-systematic name is polyvinylchloride but it is known as polychloroethene or PVC.
Ethene undergoes free radical polymerisation to give P.V.C when it is heated with a peroxide catalyst {[RO-O-R]/heat} but for GCSE purpose just mention the conditions which are: heat and catalyst.
Answer 6) d)
P.V.C is used for making pipes, guttering, and crates for fish, vegetable, bread and milk, toys, buckets and some kitchen utensils.