Download 12 Equilibrium in Chemical Reactions

Westerford and Claremont High School
Physical Science
Grade 11
June 2014
Examiner: F.Moos
Time:
Marks:
2 hours
100
Instructions

Each question must be kept separate. Start each question on a new page and hand the
questions in unstapled and in order.

Consult the data book supplied.

Approved calculators may be used.

In calculations, all formulae and working must be shown; your final answers must be calculated
correct to two significant figures.

Use blue or black ink only for your answers, other than sketches and diagrams where a sharp
pencil must be used.

A penalty of 1% will be imposed for each instruction disregarded.
Section A: Multiple Choice Questions
Question 1
Select the answer you consider to be the most correct, and indicate your choice by making a
bold, pencil cross in the corresponding block on the answer sheet.
1.1
Two forces of constant magnitude act at the same point. If the angle between them increases
from 10o to 180o, how will the magnitude of their resultant force change? It will:
A.
B.
C.
D.
1.2
Increase
Decrease
Remain the same
Increase and then decrease
(2)
A ball is dropped onto a concrete floor and bounces off the floor to the same height from which
it was dropped. Which ONE of the following laws best explains why the ball experiences an
upward force?
A.
B.
C.
D.
Newton's first law of motion
Newton's second law of motion
Newton's third law of motion
Newton's law of universal gravitation
(2)
1.3
A boy stands on a scale in a lift. The scale registers a reading of 588 N when the lift is
stationary. The lift now starts moving. At one instant during its motion, the scale registers
a reading of 600 N.
Which ONE of the following CORRECTLY describes the motion of the lift at this instant?
The lift is …
A.
B.
C.
D.
1.4
accelerating upwards.
accelerating downwards.
moving upwards at constant velocity.
moving downwards at constant velocity.
(2)
Which one of the following will result in the weakest chemical bond?
A. A shorter bond length and a double bond between the atoms.
B. A longer bond length and larger atoms.
C. Smaller atoms and a triple bond.
D. Smaller atoms and a longer bond length.
1.5
Which one of the following will contain the strongest hydrogen bonding in the liquid phase?
A.
B.
C.
D.
1.6
(2)
CH4
H2O
HF
H2S
(2)
Which one of the following gases occupies the smallest volume at STP?
A.
34 g ammonia
B.
4 g helium
C.
32 g oxygen
D.
14 g nitrogen
(2)
[ 6 x 2 = 12]
___________________________________________________
Section B: Long Questions
Question 2 - Start this question on a new page.
2.1 Force vectors P and Q were drawn to scale on the Cartesian plane shown below.
y-axis
Vector P
4
3
2
1
-4
-3
Vector Q
-2
-1
0
1
2
3
4
x-axis
-1
-2
-3
-4
2.1.1 Use a calculation to determine each of the following from the information from the Cartesian
plane:
2.1.2
(i)
The magnitude of vector P in Newtons
(2)
(ii)
The direction of vector Q measured clockwise from the positive y-axis
Use the component method to calculate the magnitude of the resultant (in Newtons) of
vectors P and Q. Be sure to show your working carefully in detail.
(3)
(4)
2.2
In an experiment to determine the unknown mass of an object, two 100 g masses and
an object of unknown mass, m, are suspended from three strings, as shown in the
diagram (not drawn to scale) below. The strings are light and inextensible. Two of the
strings run over frictionless pulleys.
When the three forces acting on knot O are in equilibrium, the angles between the two strings
and the vertical are 45° each, as shown on the diagram.
45° 45°
O
100g
100g
B
A
m
W
2.2.1
State the Triangle Rule for Three Forces in Equilibrium.
(2)
2.2.2
Determine, by ACCURATE CONSTRUCTION AND MEASUREMENT, the unknown
mass m. Use scale 10 mm : 0,1 N. Be sure to convert the masses to Newtons.
(7)
[18]
Question 3 - Start this question on a new page.
3.1
In the diagram below, a trolley B with a mass of 2 kg connected to a block A of mass
3 kg, is pulled by a constant force of 32,5 N as shown in the diagram.
Ignore the masses of the strings as well as friction.
3.1.1 Calculate the acceleration of trolley B.
(5)
3.1.2 Calculate the force exerted by trolley B on trolley A.
(2)
3.1.3 What is the force exerted by trolley A on trolley B.
(2)
3.2 A skier of mass 60 kg skies from rest down a slope inclined at an angle of 15°. The length of
the incline is 75 m. He reaches the end of the incline at an acceleration of 1,5 m·s-2.
A constant frictional force acts on the skier on his way down.
75 m
15°
3.2.1 Calculate the normal force acting on the skier.
(2)
3.2.2 Draw a labelled free-body diagram showing ALL the forces acting on the skier as he skies
down the slope.
(3)
3.2.3 Calculate the average frictional force acting on the skier during his motion down the incline.
(4)
[18]
Question 4 - Start this question on a new page.
4.1
4.2
John with a mass of 80 kg stands on a bathroom scale on the floor of an elevator. The scale
measures weight in Newton.
What will the reading on the scale be if the elevator:
4.1.1
Accelerates upwards at 2 m.s-2 ?
(3)
4.1.2
Is at rest?
(2)
4.1.3
Falls freely because the cables broke?
(2)
Satellite A with a mass of 615 kg is in orbit around the earth.
4.2.1 State Newton's law of universal gravitation in words.
(3)
4.2.2 If the earth exerts a force of 5 000 N on satellite A to keep it in orbit, calculate the height, in
kilometres, of the satellite above the surface of the earth. (Mass of the earth and radius of
the earth can be found on the data sheet)
(5)
4.2.3 Another satellite of a mass double that of satellite A, orbits at a distance twice that of
satellite A from the centre of the earth. Write down the magnitude of the force of attraction
of the earth on this satellite.
(2)
[17]
Question 5 – Start this question on a new page.
Study the table below and then answer the questions that follow:
5.1
Draw the Lewis structure for hydrogen bromide.
(2)
5.2
Explain why the bond between bromine and hydrogen is polar. (In no more than three lines)
(2)
5.3
Which of the molecules from the table will have the highest boiling point?
(1)
5.4
Give a reason for your answer in 5.3 above.
(2)
5.5
Which of the molecules in the table will have the lowest bond energy?
5.6
Using the information in the table, give a reason for your answer in 5.5 above.
5.7
Identify the specific type of intermolecular forces that exist between molecules that you identified
in 5.5 above.
(2)
5.8
Draw a potential energy curve for the hydrogen and bromine atoms as they bond. Indicate the
bond energy, the bond length and indicate point X on your graph as the point where the atoms
bond.
(Do not add any values to your graph)
(5)
(1)
(2)
[17]
Question 6 – Start this question on a new page.
6.1
A laboratory analysis of a compound indicated that it had the following chemical composition.
Na: 36,5%
6.2
S: 25,4%
O: 38,1%
6.1.1 Determine the empirical formula of the above compound.
(5)
6.1.2 How many atoms are there in 63 g of this compound.
(4)
Phosphate mining and production in South Africa is largely controlled by the Foskor group of
companies. Phosphorus is found in rock called apatite, Ca3(PO4)2. The phosphate rock is
initially prepared through a process called beneficiation. Sulfuric acid and water are added to
the apatite to produce phosphoric acid and hydrated calcium sulphate. When phosphoric acid
is added instead of sulphuric acid, triple superphosphate (calcium hydrogen phosphate) is
produced:
Ca3(PO4)2 + H3PO4
→
Ca3(HPO4)3
On a given day at Foskor’s plant in Richards Bay, 49 kg of phosphoric acid is reacted with
62 kg of calcium phosphate.
6.2.1 Calculate the theoretical yield of calcium hydrogen phosphate expected from the
reaction. Give your final answer in kg.
(5)
6.2.2 Is the phosphoric acid or the calcium phosphate the limiting reagent in this reaction?
Explain
(2)
6.2.3 If only 80 kg of calcium hydrogen phosphate is produced, calculate the percentage yield
of calcium hydrogen phosphate.
(2)
[18]
TOTAL:
100 Marks
8