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Revision Questions for the Secondary One End-of-Year Examination – Answers
1.
Option B
Increasing temperature from –220C to +420C…
…ice would melt and then boil into steam, solid sodium chloride would not change state, solid
carbon dioxide would melt and then boil into a gas, solid oxygen would melt and then boil into
a gas.
2.
Option B
At 16C, the ammonia gas and the hydrogen chloride gas have less kinetic energy than they
did at 25C. The two gases diffuse more slowly at 16C and hence the ring of ammonium
chloride takes a longer time to be formed.
3.
Option C
Elements and compounds are pure substances and therefore have fixed melting points. The
properties of a compound are different to the properties of the elements that were used to
make it. Mixtures can be separated by physical means, e.g. chromatography, distillation and
filtration. Elements can generally be considered to exist as either atoms or molecules.
4.
Option D
Ammonia is a compound, air is a mixture, sodium chloride is a compound.
Copper(II) sulfate is a compound, oxygen is an element, iron is an element.
Steel is an alloy (mixture), sodium chloride is a compound, copper(II) sulfate is a compound.
Water is a compound, carbon dioxide is a compound, sodium chloride is a compound.
5.
Option A
Hydrogen chloride, formula HCl, is a compound composed of a single hydrogen atom bonded
to a single chlorine atom. This is best represented by the arrangement of particles shown in
box A. Boxes B and D both show mixtures of two different elements. Box C show a compound
similar to water, formula H2O.
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6.
Option C
The apparatus shown can be used to separate one chemical that sublimes (changes directly
from a solid to a gas) from another chemical that does not sublime.
Iodine sublimes. Although sugar does not sublime, it will decompose to form caramel on
heating.
Solid carbon dioxide and iodine both sublime on heating.
Iodine sublimes on heating while sodium chloride does not sublime or decompose on heating.
This mixture is best suited to be separated by the apparatus shown in the diagram.
Ammonium chloride and iodine both sublime on heating.
7.
Option D
The fact that the distillate boils between 82C to 98C indicates that it is impure. To increase
the purity of the distillate, a fractionating column should be used. Water vapour would
condense on the glass beads of the fractionating column, ensuring that only pure ethanol is
collected as the distillate.
8.
Option A
Liquid water in the ground evaporates to form water vapour. The water vapour then condenses
on the plastic sheet to form liquid water. The separation technique that converts a liquid into a
vapour, and then condenses the vapour back into a liquid is distillation.
9.
Option B
For two liquids to be separated using a separating funnel or tap funnel, they must be
immiscible, e.g. oil and water.
10. Option A
Atoms that have complete valence shells are very stable and chemically unreactive. Such
atoms are said to have a noble gas electronic configuration. The innermost electron shell is
complete when it contains two electrons. The second and third electron shells are complete
when they contain eight electrons.
11. Option B
When a solid melts (or when a liquid freezes / solidifies) both solid and liquid states of matter
are present. When a liquid boils (or when a gas condenses) both liquid and gaseous states of
matter are present.
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12. Option B
Metals are good conductors of heat and electricity. They are malleable (their shape can be
changed without breaking) and ductile (can be drawn-out into wires). Metals generally have
high melting points and boiling points. Most metals have densities greater than water, meaning
that a block of metal will sink when added to water.
13. (a) The freezing point of stearic acid is 69C.
(b) The particles are closely packed together in a regular / ordered / crystalline / lattice
arrangement.
The particles vibrate about fixed positions.
(c) The stearic acid is pure.
It freezes at a constant temperature (not over a range of temperatures).
14. (a) The gas that diffuses the fastest is methane, CH4.
(b) Both carbon monoxide and nitrogen have the same relative molecular mass.
Relative molecular mass of carbon monoxide, CO = 12 + 16 = 28
Relative molecular mass of nitrogen, N2 = 14 + 14 = 28
Gases with the same relative molecular mass will diffuse at the same rate at the same
temperature.
(c) A gas will diffuse from a region of higher concentration to a region of lower concentration.
Carbon dioxide diffuses into the cells of the spongy mesophyll layer, as the concentration
of carbon dioxide gas is relatively high outside the cells and relatively low inside the cells.
Oxygen diffuses out of the cells of the spongy mesophyll layer, as the concentration of
oxygen gas is relatively high inside the cells and relatively low outside the cells.
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15.
(a) The candy contains food dyes E12 and E15.
(b) Note: The chromatogram needs to be re-numbered with the start line as “0”.
Rf value = distance travelled by spot  distance travelled by solvent
Rf value of E12 = 5  6 = 0.83
(c) Dye E12 is more soluble in the solvent used for the chromatography than dye E10.
(d) Although four food dyes are used, two of them could have the same Rf value and
therefore overlap on the chromatogram.
Note: The fact that the fourth food dye is colourless may be accepted as an answer, but it
would be pointless to add a colourless chemical to a candy in order to colour it!
(e) Pencil lead is insoluble in most solvents. It will not dissolve in the solvent used for the
chromatography, move up the filter paper, and interfere with the results.
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