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Brown's Chemistry Clinic
ANSWERS
TO SOME OF THE GCSE
TASK SHEET QUESTIONS
KS4 science and
IGCSE chemistry
(not finished)
Email
query?comment
1.
The Historic Development of the Periodic Table
(original
task sheet and the answers should be discussed and thought about
in an open-minded way)
-
Q1 Based on Antoine
Lavoisier's classification of 1789
-
(a) (i) Substance
can't be spit into simpler substances, (ii)
one or more elements chemically combined to form a new substance.
-
(b) 'light' and
'caloric', not substances at all!
-
(c) Sort of!, mainly
the element carbon, but is a mixture, but not bad for 1789?
-
(d) There oxides are
soluble in water forming acids eg litmus turns red.
-
(e) Yes all metallic
elements, doubt if they were pure though!
-
(f) Basically yes,
judging from the first three columns listed, 4th column is a problem!
-
(g) The 'earthy
elements', which are compounds, a chemical combination of a metal plus
oxygen or sulfur (both in case of barium).
-
(h) He didn't have
the high temperature, reactive metal or electrolysis 'knowledge' to
'separate' the elements in some way eg extract a reactive metal. In
other words the wrong classification was due to a lack of chemical
technical knowledge.
-
Q2 Based on the 1829
work of Johann Döbereiner
-
(a) The 'group' idea
of chemically very similar elements.
-
(b) (i) Group 1
Alkali Metals, (ii) Group 2 Alkaline Earth Metals, (iii) Group 7
Halogens.
-
Q3 Based on the work of
John Newlands 1864
-
(a) eg almost
completely genuine elements (Di was a mix of two elements), classified
roughly into groups of similar
elements, 1st real recognition of 'periodicity'
-
(b) Wider range of
elements 'quoted' in 'groups', recognised that the 'groups' had more
than 3 elements, correct to mix up metals and non-metals in same group
eg 5th column.
-
(c) Not precisely
BUT be 'fair' to him, half of column 2 is Group 1, half of column 3 is
Group 2, half of column 5 is Group 4, half of column 6 is Group 5, half
of column 7 is Group 6. (If he had put his column 1 as column 7, quite a
lot would match today!
-
(d) None
of his vertical column groups match completely but from (c) above, the
basic pattern was emerging. However column's 1 and 7 do seem
particularly mixed up compared to the modern periodic table.
-
(e) Column 4 has B
and Al, column 5 C and Si with Sn, column 6 has N and P with Sb and Bi.
-
(f) The 'Group' and
'Period' (see answer to (a))
-
Q4 Based on Dmitri
Mendeleev's Periodic Table of 1869
-
(a) In order of
'atomic weight' (we know call relative atomic mass).
-
(b) Group 0 (or 8)
The Noble Gases. These were not completely found and characterised until
the 1890's.
-
(c) Above Y is Sc,
below Al is Ga, below Si is Ge
-
(d) (i) pattern from
looking at the properties of the elements above and below 'x'. (ii)
and (iii) Sc a metal, Sc2O3 and ScCl3
(like Al), Ga metal Ga2O3 and GaCl3
(like Al), Ge a metal GeO2, GeCl4 (like C).
(BUT at a 'deeper' level Ga and Ge are semi-metals with
intermediate properties overall).
-
(e) Increased number
of known elements, groups becoming more clearly defined (he used a
double column approach which is not incorrect, ie a sort of group xA and
xB classification), order across a period much better, sufficiently
accurate to predict missing elements and their properties.
-
Q5 Based on a typical
modern version of the Periodic Table
-
(a) In order of
atomic (proton) number.
-
(b) Due to isotopic
masses, the relative atomic mass does go 'down' occasionally (there is
no obvious 'nuclear' rule that applies). BUT chemically Te is S and Se
etc. and I is like Cl and Br etc. This is now backed up by modern
knowledge of electron structure.
-
(c) Most
importantly, it is complete bar newly 'man-made' elements (see (d)
below). We now know the electronic structure of elements and can
understand sub-levels and the 'rules' in electron structure eg 2 in
shell 1 (period 1, 2 elements H to He), 8 in shell 2 (period 2, 8
elements Li to Ne), there is a sub-level which allows an extra 10
elements (the transition metals) in period 4 (18 elements, K to Kr).
this also explains the sorting out of Mendeleev's A and B double columns
in a group (but that's for much more advanced chemistry!). The periods
are complete now that we know about Noble Gases.
-
(d) In the 1940's
Glenn Seaborg was part of a research team developing the materials
required to produce the first atomic bombs dropped on Hiroshima and
Nagasaki. He specialised in separating all the substances made in the
first nuclear reactors and helped discover the series of 'nuclear
synthesised' elements beyond the naturally occurring limit of uranium (92U).
From element 93 to 109? are now known, so who know's next year+ ...?
Will the structure of the bottom part of the periodic table grow?
change? There is plenty of scope for present day, and future Mendeleev's!!!! (will
you be one of em'?).
-
Glen Seaborg was a Nobel
Prize winner and is considered one of Americas four greatest
chemists from a vote by the American Chemical Society: The others
are ...
-
Linus Pauling,
who nearly beat Crick and Watson to the structure of DNA and was,
prior to his death, still happily, and enthusiastically, writing research papers at 85
from his California beach house overlooking the Pacific, (and I've just retired at
58!).
He is one of my real chemical hero's and I've got a 2nd hand copy of
his 1950 textbook on
"Chemical Bonding" and such a revelation to any serious
student (in the 60's), probably looks a bit old-fashioned to a
modern student!
-
Wallace
Carothers who (prior to committing suicide) synthesised Nylon and
Neoprene (1st artificial rubber). He suffered from extreme
depression and his immense success seems to have offered little
comfort for him after the death of his favourite sister. Sad, but,
chemists are just another cross-section of society.
-
Robert Woodward
was a fantastic organic chemist both 'practically' and
'theoretically'.
2.
The Periodic Table - Basic Exercise
(original
task sheet)
-
Q1 (a) zig zag
line 'roughly goes through B\Al, Al\Si, Ge\As, Sb\Te, Bi\Po
-
Q2 (a) METALS:
high melting/boiling points (all solid at room temperature except mercury),
high density, good conductors of heat/electricity, shiny 'lustrous' surface,
strong material
-
(b) NON-METALS: low
melting/boiling points (can be gas, liquid or solid at room
temperature), low density, good conductors of heat/electricity, shiny
'lustrous' surface, soft or brittle if solid
-
Q3 (a) METALS:
(i) form basic oxides which react with acids to form salts, if oxide soluble
in water an alkali is formed and turn litmus blue; (ii) react with acids to
form a salt solution and hydrogen gas, (iii) readily combine with non-metals
to form ionic compounds
-
(b) NON-METALS: (i)
form acidic oxides that react with alkalis to form salts, if oxide
soluble in water it will turn litmus red; (ii) do not usually react with
acids, (iii) readily combine with metals to form ionic compounds, (iv)
combine with other non-metals to form covalent compounds.
-
Q4 (a) GROUP -
vertical column of chemically similar elements eg Li to Cs are the very
reactive Alkali Metals
-
(b) PERIOD - a whole
horizontal row of elements of varying character eg metals ==>
non-metals from left ==> right
-
(c) TRANSITION
METALS - a series of similar metals which form part of a period, they
are strong, high melting, act as catalysts, form coloured compounds
-
Q5 Li-Cs group 1,
Be-Ba group 2, B-Tl group 3, C-Pb group 4, N-Bi group 5, O-Po group 6, F-At
group 7, He-Rn group 0 or 8
-
Q6 (a)
horizontally: period 1 is H to He, period 2 is Li to Ne, period 3 is Na to
Ar, period 4 is K to Kr etc.
-
Q7 (a) Group 1 -
lithium, sodium, potassium etc., (b) Group 7 - fluorine, chlorine, bromine
etc., (c) Group 0 or 8 - helium, neon, argon etc., (d) 1st Transition Metal
series - scandium, titanium, vanadium, chromium, manganese, iron, cobalt,
nickel, copper, zinc
-
Q8 Originally
placed in order of 'atomic weight' (we now call this 'relative atomic mass')
-
Q9 Now placed in
order of atomic (proton) number.
-
Q10 Potassium is
a very reactive metal and chemically very similar to sodium and rubidium
etc. and nothing like the unreactive non-metal Noble Gases like neon and
krypton.
-
Q11 (a) 2
electrons in 1st shell, 8 in 2nd, 8 in 3rd
-
Q12 (a) B 4 outer
electrons, (b) A in group 7, (c) D 4 shells used, (d) D in Group 1 Alkali
Metal, (e) A Group 7 Halogen
-
Q13 (a) chlorine,
halogen in group 7; (b) a transition metal eg chromium, iron, copper,
nickel; (c) group 1 alkali metal eg sodium or potassium; (d) a noble gas eg
helium or neon, (e) copper, a transition metal (with gold, they are the only
two metals which are not shiny silver-grey); (f) group 1 alkali metals like
sodium or potassium; (g) bromine in group 7 halogens; (h) argon, an
unreactive noble gas.
3. The
Group 7 Halogens the properties and
uses of the elements and compounds (original
task sheet)
-
TASK 1: The properties
of the Group 7 Halogens
-
Q1 (a) fluorine,
2.7; chlorine, green gas, -102oC, -34oC,
2.8.7; bromine, dark red liquid, -7oC, 59oC;
iodine, dark/black solid, 114oC, 184oC
-
(b) gets darker
down the group
-
(c) on heating:
bromine gives orange-brown vapour, iodine gives a brilliant purple
vapour
-
Q2(a) exist as gas,
liquid or solid with low melting/boiling points
-
Q3(a)
melting/boiling points increase down the group
-
Q4 The exist as X2
molecules, 2 X atoms per molecule, where X = F, Cl, Br, I or At
-
Q5(a) form ionic
compounds with metals
-
Q6 With non-metals
they form covalent compounds
-
Q7 Chlorine: turns
damp blue litmus red before bleaching it white; iodine gives a dark
blue-black colour with starch solution
-
TASK 2: The reactivity
trend of the halogens
-
Q1a Observations of
mixing halogen solutions with halide salt solutions.
|
halogen\salt |
Potassium
chloride |
Potassium
bromide |
Potassium
iodide |
Water
blank (fair test check) |
|
chlorine water (pale green solution) |
very pale green solution - no real
colour change |
orange colour - change! |
dark colour and maybe a black
precipitate - change! |
very pale green solution |
|
bromine water (orange solution) |
pale orange to yellow solution
- no real colour change |
pale orange to yellow solution - no
real colour change |
dark colour and maybe a black
precipitate - change! |
pale orange to yellow solution |
|
iodine water (very dark
solution) |
paler dark coloured solution - no
real colour change |
paler dark coloured solution -
no real colour change |
no change (but
complicated by the formation of the darkly coloured I3-
ion) |
paler dark coloured solution |
-
Q1b The blanks is to
see if there is any colour change due to a reaction, other than the
colour observed of chlorine, bromine or iodine solution on dilution. If
there is a displacement reaction, a 'darker' colour is observed.
-
Q2a Chlorine
displaces bromine and iodine. Q2b Bromine displaces iodine. Q2c Iodine
does not displace anything here.
-
Q3a A more
reactive element will displaces a less reactive element. This rule
applies to a series of non-metals like halogens, or a series of metals.
-
Q3b The most
reactive will displace the most number of other elements, therefore the
reactivity trend for the Group 7 Halogens, from most to least reactive
is chlorine > bromine > iodine
-
Q3c The above trend
means that Group 7 Halogens get less reactive down the group with
increasing atomic number.
-
Q3d Group 0 Noble
Gases have full sub-shells of electrons (e.g. 2.8 or 2.8.8) and
therefore are electronically very stable and reluctant to undergo
chemical reactions. On the other hand, Group 7 Halogen atoms have one
electron short of a Noble Gas electron arrangement (e.g. 2.7 or 2.8.7).
These atoms do their best to gain an eighth electron to complete the
outer sub-shell either by gaining an electron (ionic bond) or sharing an
electron pair (covalent bond). This energetic desire to get that 8th
outer electron makes these elements very reactive.
-
Q4 The displacement
equations are:
-
chlorine + potassium
iodide ===> potassium chloride + iodine
-
Cl2(aq)
+ 2KI(aq) ===> 2KCl(aq) + I2(aq) (balanced)
-
and ....
-
bromine + potassium
iodide ===> potassium bromide + iodine
-
Br2(aq)
+ 2KI(aq) ===> 2KBr(aq) + I2(aq) (balanced)
-
Q5 The ionic redox
equations are, in terms of words and symbols are:
-
chlorine molecule + iodide
ion ===> chloride ion + iodine
-
Cl2(aq)
+ 2I-(aq) ===> 2Cl-(aq)
+ I2(aq) (balanced)
-
The chlorine is
reduced by electron gain and the iodide ion is oxidised by electron
loss.
-
and ...
-
bromine molecule + iodide
ion ==> bromide ion + iodine
-
Br2(aq) +
2I-(aq) ==> 2Br-(aq) +
I2(aq) (balanced!)
-
The bromine molecule
is reduced by electron gain and the iodide ion is oxidised by electron
loss.
-
Q6 All the elements
in a group have the same outer electron configuration which is the main
factor in derterming an elements chemistry.
-
Q7 When a halogen atom
reacts, it gains an electron to form a singly negative charged ion e.g.
Cl + e- ==> Cl- which has a stable
noble gas electron structure like argon. (2.8.7 ==> 2.8.8)
-
As you go down the group
from one Group 7 halogen element down to the next ..
F => Cl => Br => I ...
-
the atomic radius gets
bigger due to an extra filled
electron shell,
-
the outer electrons are
further and further from the nucleus and are also shielded by the
extra full electron shell of negative electron charge,
-
therefore the outer
electrons are less and less strongly attracted by the positive nucleus
as would be any 'incoming' electrons to form a halide ion (or shared
to form a covalent bond).
-
SO, this combination of
factors means to attract an 8th outer electron is more and more
difficult as you go down the group, so the element is less reactive as you go down the
group, i.e. less 'energetically' able to form the X- ion
(halide ion) with increase in atomic
number.
-
TASK 3: The electrolysis
of sodium chloride solution (brine)
-
Q1a Water is a
covalent liquid and there virtually no ions to carry an electric
current.
-
Q1b When acids or
salts etc. are dissolved in water the solution then contains lots of
ions and it is these charged particles which carry an electric current
as they move through the solution when a potential difference (voltage)
is applied.
-
Q2 With the current
ON you will see gas bubbles forming on the electrode. As soon as the
current is switched OFF the electrode reactions cease and no bubbling is
seen.
-
Q3a Gas 1 (formed at
cathode -ve electrode) squeaky pop with a lit splint is the test for
hydrogen.
-
Q3b Gas 2 (formed at
anode +ve electrode) turns blue litmus red but rapidly bleaches the
paper white. This is a simple test for chlorine.
-
Q3c The universal
indicator in the solution turns blue-purple, showing an alkali is
formed, which must be sodium hydroxide.
-
Q3d (i) Starch
solution gives a blue-black colour with iodine. (ii) Since chlorine can
be formed by electrolysis of sodium chloride, in principle iodine could
be produced by electrolysis of a solution of a salt of iodine e.g.
aqueous potassium iodide.
-
Q4a Positive ions
move towards the negative electrode (- cathode) and these will be
hydrogen ion H+ and sodium ion Na+. The hydrogen
ions become hydrogen gas.
-
Q4b The hydrogen
ions are reduced by electron gain to form hydrogen gas molecules.
-
Q4c Negative ions
move towards the positive electrode (+ anode) and these will be the
hydroxide ion OH- and the chloride ion Cl-. The
chloride ions become chlorine gas.
-
Q4d The chloride ion
is oxidised by electron loss to form chlorine gas molecules.
-
Q4e The ions left
are hydroxide OH- and sodium Na+, these can be
extracted to form the extremely useful alkali sodium hydroxide NaOH.
-
TASK 4: The uses of
Halogens and their compounds
-
Q1 Chlorine is a
powerful disinfectant and kills most all bacteria.
-
Q2 Uses of chlorine: PVC plastic manufacture, chlorinated hydrocarbons
(organo-chlorine compounds) are used as
solvents, pesticides and disinfectants like TCP
(trichlorophenol). It is combined
with hydrogen to make hydrogen
chloride which is dissolved in water to manufacture
hydrochloric acid. Chlorine is used in the manufacture
of household bleach, industrial bleaches for cotton, linen, wood pulp
and
domestic cleaners.
-
Q3 Hydrogen is used
in the hydrogenation of unsaturated vegetable oils to make 'solid'
margarine. It is combined with chlorine to form hydrogen chloride which
is dissolved in water to make hydrochloric acid.
-
Q4 Sodium hydroxide
is used in oven cleaners and drain cleaners. detergents, soaps, and making
sodium salts from acids including soluble aspirin since
aspirin is an insoluble organic acid.
-
Q5a Silver salts are
used in photographic film e.g. silver chloride, silver bromide and
silver iodide.
-
Q5b/c They are
chemically changed by visible light (and ultra-violet and X-rays too) to
form silver.
-
Q6a hydrogen +
chlorine ==> hydrogen chloride, which is a colourless acidic gas.
-
Q6b When dissolved
in water hydrochloric acid is formed and the solution has a pH
of about 1.
-
Q6c It is a strong
acid and reacts with alkalis to form chloride salts.
-
Q6d Hydrogen bromide
and hydrogen iodide.
-
Q6e They will be
like hydrogen chloride (Group 7 connection - Periodic Table pattern)
i.e. colourless acidic gases that will dissolve in water to form acids.
These acids will be neutralised by alkalis to form bromide or iodide
salts.
4.
The Extraction of Metals (original
task sheet)
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chemistry revision * ks4 science examinations-gcse-igcse chemistry revision * SITE PURPOSE EDUCATION - online learning
or 'self-private-tuition' using revision notes, quizzes,
practice tests involving GCSE Science CHEMISTRY in the areas of REVISING
only the CHEMISTRY-Earth Science-Radioactivity at Doc Brown's
Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges,
academy/academies or home self-study. Hopefully it will encourage
interest and understanding of Chemistry, Earth Science and Radioactivity
in any country of the world, though the site is written entirely in English. The website is designed to help
and unofficially support students/teachers revise-learn/teach the chemistry for modular
or co-ordinated examination science
courses from UK QCA based AQA, OCR (Oxford and Cambridge) Twenty First (21st) Century and Gateway Science, Edexcel
360Science ,
Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA
exams etc.
Also, national award assessments-examinations for GCSE-IGCSE-KS4-O
level-BTEC-NVQ
applied, additional and chemistry national science courses. Also covers,
mainly via quizzes the UK National KS3 SATs Science-biology/chemistry/physics (SAT revision levels 3-5
or 5-7) and covers much of the revising, learning and teaching chemistry
examinations for the
national curriculum for secondary schools and colleges. The site does
not support the content of England, Wales or Northern Ireland primary
science KS1 or KS2. The notes should also provide some background theory
for a coursework assignment or project. BUT please note that
my on-line revision notes and quizzes are no substitute for good classroom
teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers
and a copy of the syllabus which are readily downloaded from the
examination board sites, but I hope here and there they will lend a
tutoring hand on some topic, unit, module etc. For final revision you
have to be intellectually honest about what you don't know or follow, YOU have to
take the stuff to pieces, analyse what you do/do not understand
and reconstruct it so it all makes sense in the end. There is no other
way, there are no magic secrets on how to revise and learn, its mainly
down to hard work and just good old fashioned study and employing teach-yourself
strategies without the need for extra tutors and tutoring lessons. I also think
there is too much hit and miss revision using past papers (which I do NOT
supply) and not enough
systematic revision. I also hope it will help teachers in planning
lessons and developing schemes of work for science-chemistry. There are no
lesson plans on the site but there are plenty of quizzes to incorporate into
classroom activities whether photocopied or on electronic whiteboard projector
for use as self-tuition-assessment purposes and a variety of teaching and
learning styles and the images may be used in Microsoft Word documents and powerpoint projections.
The site seems to be used by a large number of home study tutors, particularly
the revision notes. An individual tutor may print out the notes for
science-chemistry learning teaching-tuition purposes and for background material
for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf files
of the notes at the moment. Neither have I time to write up many practical
laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots
of background information of chemical reactions in terms of
observations-balanced equations-reactants-products-theory etc. I also find it
difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on
what you need, what you have time for, and there are so many of them to choose
from and I do not supply past examination papers for classes. The sites
resources include revision notes, quizzes and worksheets which provide support
for home study or tuition for homework and coursework help e.g. science
investigations for any of the key stage courses indicated, but I do not supply
lesson plans. Dr W P Brown gcse
19-11-2007 * ks4 science examinations gcse-igcse chemistry
revision *
ks4 science examinations-gcse-igcse chemistry revision * ks4 science
modular courses
examinations-gcse-igcse chemistry revision * ks4 science modular courses examinations-gcse-igcse chemistry
revision * ks4 science modular courses examinations-gcse-igcse
chemistry revision * ks4 science modular courses examinations-gcse-igcse chemistry
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