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PHYSICAL SCIENCES PRACTICAL EXAMINATION

AUGUST 2016

UMLAZI DISTRICT

GRADE 12

Physical Sciences Practical Examination - 2016 Grade 12

INSTRUCTIONS AND INFORMATION

1. Write your name in the appropriate spaces on the ANSWER BOOK.

2. Answer ALL the questions in the ANSWER BOOK

3. You may use a non-programmable calculator.

4. You may use appropriate mathematical instruments.

5. Number the answers correctly according to the numbering system used in this question paper.

6. Give brief motivations, discussions, et cetera where required.

7. Round off your final numerical answers to a minimum of TWO decimal places.

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QUESTION ONE

Learners prepare an ester in the laboratory using the following apparatus and procedure.

Procedure

a. 2,5 cm3 of butanoic acid and 2,5 cm3 of ethanol are placed in a test tube.

b. A few drops of dilute 0,2 mol.dm-3 sulphuric acid is added to the mixture.

c. The contents of the test tube are shaken and placed in a water bath. Some tissue paper soaked in cold water is placed near the mouth of the test tube.

d. The water bath is heated.

e. After a while the contents of the test tube are poured into a beaker of cold water.

1.1 Give two reasons why a water bath is used in this experiment. (2)

1.2 Explain the purpose of the tissue paper soaked in cold water. (2)

1.3 In the procedure described above learners made one error.Identify the error and explain why this may not result in the production of the ester. (3)

1.4 Explain the significance of step e. (2)

1.5 Using structural formulae, write down the balanced equation for the formation of the ester.

(5)

1.6 Give the IUPAC name of this ester (2)

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Water bath

Tissue paper soaked in cold water

Hot plate

Ethanol + butanoic acid + dilute sulphuric acid


QUESTION TWO

Learners want to verify the Law of Conservation of Momentum. They place two trolleys, X and Y, on a horizontal surface with two barriers on both sides as shown below. The masses of trolleys X and Y are 500 g and 400 g respectively.

Initially both trolleys are stationary. Trolley X is equipped with a spring-loaded plunger, which is in contact with the barrier. When the spring is released, trolley X moves at a constant velocity before it collides with trolley Y. Immediately after the collision both trolleys move off in opposite directions.Ignore the effects of friction.

The velocity versus time graph below shows the motion of trolley X after the spring was released.

2.1 State TWO precautions that you will take when doing this investigation. (2)

2.2 From the graph, write down the velocity of trolley X after the collision. (2)

2.3 Calculate the magnitude of the change in velocity of trolley X during the collision. (3)

2.4 The velocity of trolley Y after collision is 0,28 m.s-1 . Show, by calculation, that this experiment verifies the Law of Conservation of Momentum. (5)

2.5 The Law of Conservation of Momentum makes reference to an “isolated system”. What is an “isolated system”? (2)

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[14]QUESTION THREE

The active ingredient in a certain antacid tablet is the carbonate ion (CO32-

(aq)). This ion reacts with the hydrochloric acid in your stomach according to the following reaction:

CO32-

(aq) + 2 HCl (aq) → 2 Cl- (aq) + H2O(l) + CO2(g)

The formation of CO2 gas is an indication that some of the acid has been neutralised and this brings relief from indigestion.

A group of learners use two of these antacid tablets to investigate one of the factors that influence the reaction rate. They follow the method and use the apparatus given below, to conduct the investigation.

Method:1. Simultaneously start a stopwatch and close the flask with the rubber stopper as

shown in the diagram below.

2. Place one antacid tablet in a flask and add 20 cm3 HCl (aq). HCl (aq) is in excess.

3. Repeat the procedure, but grind the second antacid tablet to a fine powder prior to the reaction.

4. Measure the volume of the CO2 gas formed in intervals of 30 seconds.

Apparatus:

3.1 Define the term reaction rate. (2)

3.2 Write down an investigative question for this investigation. (2)

3.3 State THREE variables that must be controlled during this investigation. (3)

3.4 The method that the learners use is not in the correct order. Rearrange the method to fulfil the aim of this investigation.(Write down only the numbers of the steps in the correct sequence.) (2)

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Rubber stopper


3.5 What is the name of the apparatus used to measure the volume of gas formed.

(1)

3.6 The following is a sketch obtained for the reaction of hydrochloric acid with a SOLID antacid tablet.

Redraw the above sketch in your answer book. On the same set of axes, sketch the curve (Q) that will be obtained for the reaction of the POWDERED antacid tablet with hydrochloric acid. Clearly label the curves P and Q on the re-drawn sketch graph. (3)

3.7 What will be the effect on reaction rate if the volume of hydrochloric acid used was increased to 40 cm3 in the first experiment.(Choose from INCREASES; DECREASES or REMAINS THE SAME.)Explain the answer. (3)

[16]

QUESTION FOUR

In an experiment learners use the reaction of magnesium with excess hydrochloric acid to investigate the effect of concentration on reaction rate.

Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)

4.1 Write down a hypothesis for this investigation. (2)

4.2 The graph of volume of H2 (g) vs time is given below.

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4.2.1 Calculate the rate of the reaction at t = 2 minutes. (4)

4.2.2 Calculate the AVERAGE rate of reaction for the complete reaction. (4)

[10]

QUESTION FIVE

5.1 A 250 cm3 standard solution of oxalic acid, (COOH)2 ∙ 2H2O, of concentration 0,1 mol.dm-3 is prepared in the laboratory.

5.1.1 What is a standard solution? (1)

5.1.2 Calculate the mass of oxalic acid needed to prepare this solution. (4)

5.2 This solution is now used to standardise a NaOH solution. The following is a brief summary of the steps taken.

5.2.1 Write down the name of apparatus A (1)

5.2.2 Identify apparatus B (1)

5.2.3 What is the name of apparatus C? (1)

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Step 1Apparatus A is used tomeasure the precise volume of oxalic acid which is then transferred to apparatus C.

Step 2A suitable indicator isadded to the oxalic acid

Step 3The sodium hydroxide is added from apparatus B into apparatus C. The contents of C are constantly swirled.


The following indicators are available for this titration:

INDICATOR pH RANGEBromothymol blue 6,0 – 7,6Phenolphthalein 8,3 – 10,0Methyl Orange 3,1 – 4,4

5.2.4 Which one of the above indicators is most suitable to indicate the endpoint in this titration?Give a reason for your answer.

(2)

The titration is done three times WITHOUT FILLING APPARATUS B BETWEEN TITRATIONS. The three titrations are referred to as Trials 1, 2 and 3. The diagram shows a section of apparatus B for each of the three trials.

5.2.5 Calculate the volume of NaOH used in each of the trials. (3)

5.2.6 Write down a balanced equation for the reaction that takes place. (3)

5.2.7 Calculate the concentration of the NaOH solution. (5)

5.2.8 During the titration, some of the NaOH splashed onto the sides of apparatus C. This was washed into the solution using distilled water. How will the addition of distilled water affect the answer to question 5.2.7 above? (Choose from: INCREASES, DECREASES or REMAINS THE SAME)Give a reason. (2)

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QUESTION SIX

Learners do an experiment to determine the internal resistance of a battery. They use the following circuit in which a variable resistor Q is used to adjust the total resistance of the circuit. In order to take the voltmeter and ammeter readings, the switch is closed for a SHORT PERIOD. The switch is then opened.

They record their results in the following table.

Current (A) Voltage (V)2 6,03 4,54 3,05 1,5

6.1 Why must the switch be closed for short periods of time while taking the readings? (1)

6.2 Write down the controlled variable for this experiment. (1)

6.3 Use the above results to draw a graph of the voltmeter reading V versus the ammeter reading I on the graph paper provided. Plot the values of V on the vertical axis and I on the horizontal axis. (4)

6.4 Use the graph to determine:

6.4.1 The internal of the battery. (4)

6.4.2 The emf of the battery. (1)

6.4.3 The voltmeter reading when the current through the variable resistor is 1 A. (1)

6.5 Another resistor is connected in series to Q. How will this affect the internal resistance of the battery?Choose from INCREASES, DECREASES or NO EFFECT (1)

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A

V

S

Q


6.6 Another group of learners conducting the same experiment set up their circuit as shown in the diagram below. They notice that their ammeter reading is zero EVEN when the switch is CLOSED.

Why is the ammeter reading zero? (1)

[14]

QUESTION SEVEN

Learners want to determine the equivalent resistance of two resistors connected in PARALLEL.

They use a circuit with the following components: a battery, two resistors R1 and R2 of unknown resistance, connecting wires, switch, two ammeters and a voltmeter. The internal resistance of the battery and the resistance of the connecting wires are negligible and can be ignored.

They connect the components of the circuit, close the switch and record the following readings:

Current through R1 = 0,3 ACurrent through R2 = 0,2 AVoltage across R1 = 6,0 V

7.1 Draw the circuit diagram. (2)

7.2 Use this information to calculate the equivalent resistance of R1 and R2. (5)

[7]

Total Marks: [100]Data

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A

V

S

Q

Relative atomic masses: C = 12 ; O = 16 ; H = 1

1R

= 1R1

+ 1R2

+ .. .R = R1 + R2+ . ..R = VI

n = mM

c = nV


Answer Sheet : Question 6.3

Name: _______________________________________

Grade: _________

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