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Past-paper
questions (5)
Francine
Taylor-Campbell, Contributor
1.
Two of the isotopes of phosphorous
are 32P, which is radioactive, and
31P, which is not radioactive.
(a)
Explain the meaning of isotopes and
of radioactive in this statement.
(ii)
How many electrons, protons and neutrons
are present in one atom of 32P?
(iii)
Give one use of a named radioactive
isotope.
(b)
An element is in Group VI of the Periodic
Table. Give two chemical properties
which this element is likely to have.
(c)
Name one of the elements in Group
O of the Periodic Table. Give a use
for this element.
ANSWERS
1a.
Isotopes are elements having the same
atomic number (protons) but different
mass number (neutrons). A substance
is said to be radioactive if its nucleus
is unstable and readily breaks down
to give smaller atoms and emits radiation.
(ii)
32P has 15 protons and
15 electrons. # neutrons = 32 - 15
= 16
(iii)
14C is used in determining the age
of rocks
(b)
An element in Group VI would be an
oxidising agent and would form covalent
compounds with non-metals.
(c)
Helium is in Group O which is also
known as Group 8. It is used to fill
weather balloons.
2.
This question is based on the following
oxides; carbon dioxide, copper II
oxide, sodium oxide, carbon monoxide,
silicon dioxide and sulphur dioxide.
(a)Which
oxide has a macromolecular structure?
(b)Which
oxide is used to bleach wood pulp
in the manufacture of paper?
(a)
Which oxides are acidic and which
are basic?
(b)
Which oxides are common atmospheric
pollutants?
(c)
Which oxide is the main constituent
of sand?
(d)
Which oxide produces a blue solution
when heated with dilute sulphuric
acid?
ANSWERS
2.
(a) Silicon dioxide
(b)
Sulphur dioxide
(c)
Carbon dioxide, silicon dioxide and
suphur dioxide are acidic while copper
II oxide and sodium oxide are basic.
(d)
Carbon monoxide and sulphur dioxide
(e)
Silicon dioxide
(f)
Copper II oxide ( CuO + H2SO4
= CuSO4 blue + H2O)
3.
Explain the following terms. In each
case, give a specific example to illustrate
your answer. In your answers, use
formulae or symbols as appropriate.
(a)
Relative molecular mass, Mr
(b)
Allotropes of an element
(c)
Cracking
(d)
Corrosion
(e)
Electrolysis
(f)
Anhydrous salts
(g)
Saturated solution
(h)
Hard water
(i)
Hydrocarbon
ANSWERS
3.
(a) Relative molecular mass refers
to the ratio of the mass of the molecule
to 1/12 the mass of carbon-12. The
Mr of CO = 12 + 16 = 28
(b)
Allotropes are forms of the same element
having different structural formulae
but existing in the same state. They
possess the same chemical properties
but different physical properties.
For example, Diamond (C) and graphite
(C)
(c)
Cracking is the process of breaking
up large hydrocarbon molecules into
smaller ones. For example, C9H20
==== C4H8 +
C5H12 Nonane
breaks up to give butene and pentane.
(d)
Corrosion is the eating away of a
solid surface (metal) by the action
of air, moisture and pollutants. For
example, iron corrodes to form rust
which is hydrated iron III oxide (Fe2O3.xH2O)
(e)
Electrolysis refers to the decomposition
of a substance by the passing of electric
current through it. For example, molten
NaCl gives Na and Cl2 when
electrolysed.
(f)
Anhydrous salts are those that have
lost their water of crystallisation.
Eg CuSO4 (white) from CuSO4.5H2O
(blue)
(g)
Saturated solution is one which contains
as much solute as can be dissolved
in it at a given temperature.
(h)
Hard water refers to water that does
not lather easily with soap due to
dissolved calcium and magnesium salts.
CaSO4, MgSO4,
Ca(HCO3)2 and
Mg(HCO3)2
(i)
Hydrocarbon is a substance containing
only carbon and hydrogen. For example,
CH4 is a hydrocarbon.
Francine
Taylor-Campbell is an independent
contributor. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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