QUANTITATIVE ASPECTS OF CHEMICAL REACTION

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TEACHER RESOURCES

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GR 12 Activity

1.1. Two blocks of mass M kg and 2,5 kg respectively are connected by a light, inextensible string. The string runs over a light, frictionless pulley, as shown in the diagram below. The blocks are …

Source: GR 12 Activity

Doppler effect

The data below was obtained during an investigation into the relationship between the different velocities of a moving sound source and the frequencies detected by a stationary listener for each velocity. The effect of wind was ignored in this investigation. 1.Write down the dependent variable for this investigation.(1)

2.State the Doppler effect in words. (2)

3.Was the sound source moving TOWARDS or AWAY FROM the listener? Give a reason for the answer. (2)

4.Use the information in the table to calculate the speed of sound during the investigation. (5)

5. The spectral lines of a distant star are shifted towards the longer wavelengths of light. Is the star moving TOWARDS or AWAY FROM the Earth? (1) 

QUESTION 2

The Doppler effect is applicable to both sound and light waves. It also has very important applications in our everyday lives.A hooter on a stationary train emits sound with a frequency of 520 Hz, as detected by a person standing on the platform. Assume that the speed of sound is 340 m∙s-1 in still air.

1. Calculate the:

1.1 Wavelength of the sound detected by the person (2)

1.2 Wavelength of the sound detected by the person when the train moves towards him/her at a constant speed of 15 m∙s-1 with the hooter still emitting sound (6)

2.Explain why the wavelength calculated in QUESTION 6.1.1 differs from that obtained in QUESTION 1.2. (2)

3. Use your knowledge of the Doppler effect to explain red shifts (2) 

Waves,Sound & light

QUESTION 1

A diamond glitters in light because of its high refraction index of 2,42 and the small critical angle of the diamond-air boundary.

1. Calculate the critical angle of a diamond-air interface.
Take the refraction index of air as 1. (4)

The angle of incidence of light at the diamond-air interface is increased to 30°.

2. Redraw the diagram below and complete the path of ray of light. (2) 3. Name the phenomenon that will now be observed at the diamond-air interface. (1)
4. What are the TWO CONDITIONS that are necessary for the phenomenon in QUESTION 9.3 to happen? (2)
5. Name the medical instrument used to examine internal parts of the body that makes use of the phenomenon in QUESTION 9.3. (1)                                     

QUESTION 2

Learners passed light from a ray box through a rectangular glass block to verify Snell’s law. The results obtained are used to draw the graph below. 1.Write down the independent variable. (1)
2.Write down the variable that must be controlled. (1)
3.Write down the conclusion that can be obtained from the graph. (2)
4.USE THE GRAPH to determine the refraction index of the glass block. (4)      

Work energy & power questions

Two stationary steel balls, A and B, are suspended next to each other by massless, inelastic strings as shown in Diagram 1 below. Ball A of mass 0,2 kg is displaced through a vertical distance of 0,2 m, as shown in Diagram 2 above. When ball A is released, it collides elastically and head-on with ball B. Ignore the effects of air friction.
4.1. What is meant by an elastic collision? (2)
Immediately after the collision, ball A moves horizontally backwards (to the left). Ball B acquires kinetic energy of 0,12 J and moves horizontally forward (to the right).
Calculate the:
4.2.Kinetic energy of ball A just before it collides with ball B (Use energy principles only.) (3)
4.3.Speed of ball A immediately after the collision (4)
4.4.Magnitude of the impulse on ball A during the collision (5)                      

GR 12 Activity

1.1. Two blocks of mass M kg and 2,5 kg respectively are connected by a light, inextensible string. The string runs over a light, frictionless pulley, as shown in the diagram below.
The blocks are stationary. 1. State Newton’s THIRD law in words. (2)
2. Calculate the tension in the string. (3)

The coefficient of static friction (μs) between the unknown mass M and the surface of the table is 0,2.

3. Calculate the minimum value of M that will prevent the blocks from moving. (5)

The block of unknown mass M is now replaced with a block of mass 5 kg. The 2,5 kg block now accelerates downwards. The coefficient of kinetic friction (µk) between the 5 kg block and the surface of the table is 0,15.

4. Calculate the magnitude of the acceleration of the 5 kg block. (5)

1.2. A small hypothetical planet X has a mass of 6,5 x 1020 kg and a radius of 550 km.
Calculate the gravitational force (weight) that planet X exerts on a 90 kg rock on this planet’s surface. (4)


Q2

A bullet of mass 20 g is fired from a stationary rifle of mass 3 kg. Assume that the bullet moves horizontally. Immediately after firing, the rifle recoils (moves back) with a velocity of 1,4 m∙s-1.

1. Calculate the speed at which the bullet leaves the rifle. (4)

The bullet strikes a stationary 5 kg wooden block fixed to a flat, horizontal table. The bullet is brought to rest after travelling a distance of 0,4 m into the block. Refer to the diagram below. 2. Calculate the magnitude of the average force exerted by the block on the bullet. (5)

3. How does the magnitude of the force calculated in QUESTION 2 compare to the magnitude of the force exerted by the bullet on the block? Write down only LARGER THAN, SMALLER THAN or THE SAME. (1)                                                                                               

Q3

A 5 kg block, resting on a rough horizontal table, is connected by a light inextensible string passing over a light frictionless pulley to another block of mass 2 kg. The 2 kg block hangs vertically as shown in the diagram below. A force of 60 N is applied to the 5 kg block at an angle of 10o to the horizontal, causing the block to accelerate to the left.
The coefficient of kinetic friction between the 5 kg block and the surface of the table is 0,5. Ignore the effects of air friction.

1. Draw a labelled free-body diagram showing ALL the forces acting on the 5 kg block. (5)

2. Calculate the magnitude of the:

2.1. Vertical component of the 60 N force (2)
2.2.Horizontal component of the 60 N force (2)
2.3. State Newton’s Second Law of Motion in words. (2)

Calculate the magnitude of the:

1.Normal force acting on the 5 kg block (2)
2.Tension in the string connecting the two blocks (7)


The letters A to F in the table below represent six organic compounds. 1.1. Write down the:
1. NAME of the functional group of compound B NAME of the functional group of compound B (1)
2.Homologous series to which compound C belongs (1)
3.Type of polymerisation reaction that produces compound F (1)
1.2. Write down the IUPAC name of:
1. The monomer used to prepare compound F (1)
2. Compound C (2)
3. Compound D (2)
1.3. Write down the NAME or FORMULA of each product formed during the complete combustion of compound D. (2)
1.4. Write down the structural formula of:
1.Compound B (2)
2.A CHAIN ISOMER of compound A (2)

A laboratory assistant uses bromine water to distinguish between compounds D and E. She adds bromine water to a sample of each in two different test tubes. She observes that the one compound decolourises the bromine water immediately, whilst the other one only reacts after placing the test tube in direct sunlight.

1.5. Write down the:
1. Letter (D or E) of the compound that will immediately decolourise the bromine water (1)
2. Name of the type of reaction that takes place in the test tube containing compound D (1)
3. Structural formula of the organic product formed in the test tube containing compound E (2)                                                                                                                                                                

Gr12 test yourself

Ball A is projected vertically upwards at a velocity of 16 m∙s-1 from the ground. Ignore the effects of air resistance. Use the ground as zero reference.

1.Calculate the time taken by ball A to return to the ground.(2)
2.Sketch a velocity-time graph for ball A.(2)

Show the following on the graph:

(a) Initial velocity of ball A (1)
(b) Time taken to reach the highest point of the motion (1)

ONE SECOND after ball A is projected upwards, a second ball, B, is thrown vertically downwards at a velocity of 9 m∙s-1 from a balcony 30 m above the ground. Refer to the diagram below.
Calculate how high above the ground ball A will be at the instant the two balls pass each other. (6) The letters A to D in the table below represent four organic compounds.
Use the information in the table to answer the questions that follow.
1.1.Write down the:
1. Letter that represents a ketone 
2.Structural formula of the functional group of compound C  3.General formula of the homologous series to which compound A belongs  4.IUPAC name of compound A  5.IUPAC name of compound B  1.2.Compound D is a gas used in cigarette lighters
1.To which homologous series does compound D belong?  2.Write down the STRUCTURAL FORMULA and IUPAC NAME of a structural isomer of compound D  3.Is the isomer in QUESTION 1.2.2 a CHAIN, POSITIONAL or FUNCTIONAL isomer?  1.3.Compound D reacts with bromine (Br2) to form 2-bromobutane. Write down the name of the:
1.Homologous series to which 2-bromobutane belongs  2.Type of reaction that takes place The flow diagram 1 below shows two organic reactions. The letter P represents an organic compound. Use the information in the flow diagram to answer the questions that follow. Write down the:
1.Type of reaction of which Reaction 1 is an example (1)
2.STRUCTURAL FORMULA of the functional group of ethyl propanoate (1)
3.IUPAC name of compound P (1)
Reaction 2 takes place in the presence of an acid catalyst and heat. Write down the:
4.Type of reaction of which Reaction 2 is an example (1)
5.NAME or FORMULA of the acid catalyst (1)
6.STRUCTURAL FORMULA of the alkene (2) Write down the: Diagram 2
1.STRUCTURAL FORMULA of the monomer that is used to prepare the above polymer (2)
2.Type of polymerisation reaction (ADDITION or CONDENSATION) that is used to prepare this polymer (1) Four compounds of comparable molecular mass are used to investigate the effect of functional groups on vapour pressure. The results obtained are shown in the table below.

1.Define the term functional group of an organic compound. (2)
2.Which ONE of the compounds (A, B, C or D) in the table has the:
2.1.Highest boiling point
(Refer to the vapour pressures in the table to give a reason for the answer.)
2.2.Weakest intermolecular forces (1)
2.3.Refer to the type of intermolecular forces to explain the difference between the vapour pressure of compound A and compound B. (3)
2.4.The vapour pressures of compounds C and D are much lower than those of compounds A and B. Name the type of intermolecular force in A and B that is responsible for this difference. (1)
2.5.Briefly explain the difference in vapour pressure between compound C and compound D (2)

2.6.During a combustion reaction in a closed container of adjustable volume, 8 cm3 of compound A (butane) reacts in excess oxygen according to the following balanced equation:

2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)

If the initial volume of the oxygen in the container was 60 cm3, calculate the TOTAL volume of the gases that are present in the container at the end of the reaction. All the gases in the container are at the same temperature and pressure. (5)


Test yourself GR11

Consider the following molecules and answer the questions that follow.

Consider the following molecules and answer the questions that follow.
A.NH3
B.CO2
C.C2H2
D.H20
E.BH3
Which molecule:
1.1.1 Contains a triple bond?  1.2 Is trigonal planar?  1.3 Is angular in shape and contains a centre atom with two lone pairs?  2.Which TWO molecules can form a dative covalent bond with a hydrogen ion?  1. Draw a Lewis structure of the CO2 molecule.  2 Briefly explain why the bonds shown in your answer to
QUESTION .1 are considered to be “polar covalent”. Refer to the difference in electronegativity of the atoms involved.  

During a mountain climbing exercise, Ferial, mass 50 kg, is suspended from an inelastic piece of nylon rope, fixed to a vertical cliff at X on the cliff. She pushes her legs against the cliff so that they make an angle of 45° with the cliff, as indicated in figure. The angle that the rope makes with the cliff is 20°.
Point Y is in equilibrium.
2.1 Explain what is meant by Point Y is in equilibrium.  2.2 Draw a FORCE DIAGRAM showing all the forces acting on point Y.  2.3 Determine by means of ACCURATE CONSTRUCTION and MEASUREMENT.
(use the scale 10 mm: 50 N and indicate at least TWO angles):
2.3.1 The magnitude of the force which the rope exerts on her. 2.3.2 The magnitude of the force exerted by her legs. A 6 kg block on a horizontal rough surface is joined to a 2 kg block by a light, inelastic string running over a frictionless pulley. The frictional force between the 6 kg block and the table is 11,76 N. A downwards force of 2 N is applied to the 2 kg block as indicated in the diagram below.
1. State Newton’s Second Law of motion in words. (2)
2.Draw a free-body diagram showing ALL the forces acting on the 6 kg block.(4)
3.Calculate:
3.1. The magnitude of the acceleration of the 6 kg block. (5)
3.2.The magnitude of the tension (T) in the string connecting the two blocks.(2)

4. The rough surface is replaced by a smooth frictionless surface.
How will this change affect the answer in QUESTION 3.1? Write only INCREASES, DECREASES or REMAINS THE SAME. (1) 