SUBJECT Science: Paper II - DATE 19 July 2018

Chemistry
GRADE 10 MARKS 127
EXAMINER Mrs Jooste MODERATOR Mrs Angelova
Mr McCoy
NAME DURATION 120 minutes
CLASS

LOW
50% HIGH ORDER 50%
ORDER

INSTRUCTIONS
1. This examination consists of 10 page. A separate information sheet and an
answer sheet are provided.
2. It is in your own interest to write legibly and to present your work neatly.
3. Answer questions on the folio paper provided, except for questions 1, 5.1.4
and 8.2.2 (which will be answered on the answer sheet).
4. Start each question on a new page.
5. Record all answers to two decimal places.
6. Rough work and planning may be done as long as it is clearly indicated as
rough work. Rough work will not be marked.

Question 1 2 3 4 5 6 7 8 Total
Marks 12 18 18 23 24 10 7 15 127
QUESTION 1: MULTIPLE CHOICE 12 MARKS
On the answer sheet make a cross (X) in the box corresponding to the letter which
you consider to be the most correct.
1.1 What does the atomic mass in the Periodic Table indicate? (2)
A. Number of protons.
B. Number of protons plus number of electrons.
C. Number of protons plus number of neutrons.
D. Number of electrons
1.2 Which subatomic particle has a charge and negligible mass? (2)
A. Neutron
B. Electron
C. Proton
D. Nucleon
1.3 The tendency of atoms to achieve the stable electron configuration of a
noble gas is known as: (2)
A. Valency
B. Octet rule
C. Covalent bond
D. Valence
1.4 What is the molecular shape of ammonia? (2)
A. Tetrahedral
B. Pyramidal
C. Angular
D. Linear
1.5 Which ONE of the substances below contains a double bond? (2)
A. CO2
B. NH3
C. H2O
D. CH4
1.6 A cation is formed when: (2)
A. A non-metal loses electrons
B. A metal gains electrons
C. A metal loses electrons
D. A non-metal gains electrons

Grade 10 2 of 10 Science: Paper II - Chemistry

QUESTION 2: THE ATOM 18 MARKS
2.1 An atom is the smallest particle of an element that can exist. Explain why
a neutral atom has no overall charge. Refer to sub-atomic particles in your
explanation. (2)
2.2 Consider the electron configuration of some unknown atoms (A-E) in their
ground state:

Atom Electron configuration

(sp notation)

A 1s2

B 1s22s22p3

C 1s22s22p6

D [Ne]3s2

E 1s22s22p63s23p4

2.2.1 Define the term ground state. (2)

2.2.2 Which atom/s in the table has/have a stable electron
configuration? (2)
2.2.3 Draw a Bohr model for atom B. (2)
2.2.4 Draw an Aufbau diagram representing atom D. (2)
2.2.5 Would you expect atom E to undergo REDUCTION or
OXIDATION? Refer to the electron configuration in your
reasoning. (2)
2.2.6 What information regarding electron structure is given in an
Aufbau diagram that is not in a Bohr diagram? (1)
2.3 The electron configuration of an atom is illustrated below:

2.3.1 What is the chemical symbol of this element? (1)

2.3.2 How many nucleons does this element have? (1)
2.3.3 Define the term valency. (2)
2.3.4 What is the valency of this element? (1)

Grade 10 3 of 10 Science: Paper II - Chemistry

QUESTION 3: CRYSTAL LATTICES 18 MARKS
3.1 Potassium nitrate dissolved in soil water is readily absorbed by plants.
3.1.1 Write the chemical formula for potassium nitrate. (2)
The diagram below shows potassium nitrate dissolving in water.

Potassium Water
nitrate crystal molecule

3.1.2 Draw a Couper diagram of a water molecule. Use appropriate

symbols to indicate the polarity of the bonds. (3)
3.1.3 Label the ions shown by A and B. (2)
3.1.4 Refer to the polarity of the water molecules to explain their
orientation around the dissolved ions, as shown in the diagram
above. (3)
3.2 Oxygen reacts with magnesium to form magnesium oxide.
3.2.1 Write down the half reaction that magnesium undergoes in this
reaction. (2)
3.2.2 What is the name given to this half reaction? (1)
3.2.3 Explain why magnesium has a high boiling point and melting point
compared to oxygen. Refer to intermolecular forces, as well as
intramolecular bonds in your answer (3)
3.2.4 Consider the model of the magnesium crystal lattice shown below.
Describe what characteristic of the structure makes magnesium a
good conductor of electricity and heat. (2)

Grade 10 4 of 10 Science: Paper II - Chemistry

QUESTION 4: CRYSTAL LATTICES & ISOTOPES 23 MARKS
4.1 Lead is a metal used in batteries, pigments, sheeting and pipes. Two
physical properties of lead are that it is ductile and malleable.
4.1.1 Explain what is meant by the terms in bold. (2)
4.1.2 Relate the two properties above to the intramolecular bonding
present in solid lead. (2)
4.2 The most important source of lead is the mineral commonly known as
galena, or lead(II) sulphide.
4.2.1 Write the chemical formula of lead(II) sulphide. (1)
4.2.2 Name the type of intramolecular bonding found in lead(II) sulphide. (1)
4.2.3 Use a Lewis diagram to illustrate the reaction beween lead and
sulphur to form lead(II) sulphide. (4)
4.2.4 Explain why lead(II) sulphide does not conduct electricity in its
crystalline form. (3)
4.3 There are two main naturally occurring isotopes of Sulphur: 32S and 34S.
4.3.1 Define isotope. (2)
4.3.2 The atomic mass of a sample of sulphur is 32,065 amu. Calculate
the percentage abundance of 32S and 34S. (4)
4.4 Carbon is one of the elements that can be found as different allotropes.
4.4.1 Define the term allotrope. (2)
4.4.2 Consider the diagram of a carbon allotrope below: carbon atoms in
nanotubes are bonded like a single layer of atoms in graphite. Use
your knowledge of the structure of graphite to explain why
nanotubes are used as lubricants. (2)

Grade 10 5 of 10 Science: Paper II - Chemistry

QUESTION 5: DISCRETE MOLECULES & SCIENTIFIC SKILLS
24 MARKS
5.1 Halogens are a group of non-metals located in Period VII. The table below
provides the dimensions and thermal properties of common halogens.

Halogen Atomic Melting Boiling Phase at

radius (pm) point point room
(ºC) (ºC) temperature

Fluorine 42 -220,0 -188 Gas

Chlorine 79 -101,0 -35 Gas

Bromine 94 -7,3 59 Liquid

Iodine 115 114,0 184 Solid

5.1.1 Define intermolecular force. (2)

5.1.2 Name the intermolecular force that exists between halogen
molecules. (1)
5.1.3 Write the atomic radius for bromine in metres using scientific
notation. (2)
5.1.4 An incomplete graph of boiling point versus atomic radius for the
four halogens is shown in the answer sheet. Complete the graph
provided in the answer sheet by:
a. Writing labels for the x and y axes (2)
b. Providing a suitable scale for the x axis (1)
c. Drawing in a line of best fit (1)
d. Providing a suitable title for the graph (2)
5.2 Answer the questions that follow using the table above and your graph:
5.2.1 What trend can be established with respect to boiling point and
atomic radius? (2)
5.2.2 Explain the trend in the boiling point of the four halogens. (4)
5.3 Explain why iodine is a solid at room temperature, while the other
halogens are liquid or gas. Refer to the special type of structure that
occurs in iodine. (4)
5.4 Halogens form non-polar molecules.
5.4.1 What type of dipole is formed in a halogen molecule? (1)
5.4.2 Explain how this type of dipole forms. (2)

Grade 10 6 of 10 Science: Paper II - Chemistry

QUESTION 6: DISCRETE MOLECULES 10 MARKS
The table below lists the boiling points (BP) of Group V hydrides.
Group V Period BP (oC)
NH3 2 -33
PH3 3 -88
AsH3 4 -55
SbH3 5 -17

When the BP of each Group V hydride is plotted versus its Period number in the
periodic table, a general trend can be observed for Periods 3, 4 and 5 (see the graph
below). Ammonia (Period 2) does not follow this general trend.

6.1 Consider the AsH3 molecule (As is arsenic).

6.1.1 Show that AsH3 will form a polar molecule. Refer to
electronegativity difference, shape and electron cloud symmetry in
your explanation. (4)
6.1.2 Name the intermolecular force that occurs between AsH3
molecules. (1)
6.1.3 Give the chemical name of AsH3. (1)
6.2 Consider the boiling point of ammonia.
6.2.1 Name the intermolecular force responsible for the relatively high
BP of this molecule. (1)
6.2.2 State the three characteristics of the ammonia molecule that are
responsible for the force named at 6.2.1. (3)

Grade 10 7 of 10 Science: Paper II - Chemistry

QUESTION 7: CRYSTAL LATTICES 7 MARKS
Silicon dioxide has a very high melting point of approximately 1700 C. It is used to
make glass and to line the inside of furnaces.
7.1 Name the type of crystal lattice that silicon dioxide forms. (2)
7.2 Explain why the forces in the crystal lattice named at 7.1 are not
intermolecular. (2)
7.3 Explain fully the high melting point of silicon dioxide. (2)
7.4 Name another substance that forms the same type of crystal lattice. (1)

Grade 10 8 of 10 Science: Paper II - Chemistry

QUESTION 8 (START ON A NEW PAGE) 15 MARKS
8.1 Whole body hypothermia is caused by a change in blood viscosity due to a
drop in temperature. A researcher set up an experiment to measure the
viscosity of blood at different temperatures using a bubble viscometer. She
obtained the following results:

Blood temperature (ºC) Relative viscosity (no unit)

35 1,86

29.5 2.0

24.5 2.6

22.5 2.9

8.1.1 Define the term viscosity. (2)

8.1.2 Identify the two errors made by the researcher in compiling the
data in the table. (2)
8.1.3 Name the dependent variable in her experiment. (2)
8.2 Consider the graph of relative viscosity versus temperature below, not
starting at zero.

8.2.1 Could the data obtained be considered reliable? Give two reasons
for your answer. (3)

Grade 10 9 of 10 Science: Paper II - Chemistry

 8.2.2 On your answer sheet - Find the value of relative viscosity of
blood at 26 C. Make appropriate markings with clear dotted lines
on the graph to assist you. (2)
8.2.3 Consider the relationship that could exist between temperature
and viscosity. Write this relationship in words. (2)
8.2.4 Describe a simple calculation that should be performed on the
tabulated data to confirm the relationship stated in 8.2.3. (2)

END OF PAPER

Grade 10 10 of 10 Science: Paper II - Chemistry