basic education - smartlearner the diagram below represents a part of an electrochemical cell used...

Physical Sciences P2 1 September 2014 Preparatory Examination NSC

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MARKS : 150

TIME : 3 Hours

This question paper consists of 15 pages and 4 Data Sheets.

GRADE 12

NATIONAL SENIOR CERTIFICATE

Basic Education

KwaZulu-Natal Department of Basic Education

REPUBLIC OF SOUTH AFRICA

PHYSICAL SCIENCES: CHEMISTRY (P2)

PREPARATORY EXAMINATION

SEPTEMBER 2014



INSTRUCTIONS AND INFORMATION TO CANDIDATES 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. Data sheet and periodic table are attached for your use. 7. Give brief motivations, discussions, et cetera where required.



QUESTION 1: MULTIPLE – CHOICE QUESTIONS Four options are provided as possible answers to th e following questions. Each question has only ONE correct answer. Write o nly the letter (A – D) next to the question number (1.1 – 1.10) in the ANS WER BOOK. 1.1 An organic compound that is always found in alcoholic drinks:

A CH3OH

B C6H10 C C2H5OH D C6H5(CH3) (2) 1.2 In which one of the following alternatives are the three compounds listed in order of their increasing boiling point? A pentanoic acid, pentane, pentan-1-ol B pentan-1-ol, pentane, pentanoic acid C pentane, pentan-1-ol, pentanoic acid D pentane, pentanoic acid, pentan-1-ol (2) 1.3 Which one of the following correctly shows the two homologous series which react together to produce esters?

A Carboxylic acid Haloalkane B Alcohol Alkene C Haloalkane Ketone D Carboxylic acid alcohol

(2) 1.4 Magnesium reacts with sulphuric acid to liberate hydrogen gas. Which one of the set of conditions for the sulphuric acid will ensure the highest rate of hydrogen gas released?

Temperature ( oC) Volume (cm 3) Concentration (mol.dm -3) A 20 50 1 B 20 100 2 C 40 100 1 D 40 50 2

(2)



1.5 The following is the Maxwell-Boltzmann energy distribution curve for a reaction at four different temperatures. E represents the activation energy for the reaction. Which one of these curves represent the reaction with the highest rate? A 1 B 2 C 3 D 4 (2) 1.6 The air pollutant sulphur dioxide (SO2) can be removed from a gas mixture by passing the mixture over calcium oxide according to the reaction:

CaO(s) + SO2(g) ⇌ CaSO3 (s) If the equilibrium concentration of SO2(g) at 25oC is equal to 0,01 mol.dm-3, the value of the equilibrium constant at this temperature will be:

A 200 B 150 C 100 D 50 (2) 1.7 Consider the following reaction equation:

NH3(g) + H2O(ℓ) ⇌ NH4+ (aq) + OH-(aq)

The two Bronsted-Lowry bases in the reaction equation are: A NH3 and H2O B NH4

+ and OH- C H2O and NH4

+ D NH3 and OH- (2)



1.8 The cell notation for a standard Zn – Cu electrochemical cell is: A Cu2+(aq) / Cu(s) // Zn(s) / Zn2+(aq) B Zn(s) / Zn2+(aq) // Cu2+(aq) / Cu(s) C Cu(s) / Zn2+(aq) // Cu2+(aq) / Zn(s) D Zn(s) / Zn2+(aq) // Cu(s) / Cu2+(aq) (2) 1.9 The diagram below represents a part of an electrochemical cell used for refining copper. The impure copper contains silver metal and zinc metal. Which ONE of the following half-reactions will take place at electrode X? A Ag+ +e- → Ag B Cu → Cu2+ + 2e- C Cu2+ + 2e- → Cu D Zn2+ + 2e- → Zn (2) 1.10 What is name of the process used for the industrial preparation of sulphuric acid? A Haber process B Ostwald process C Contact process D Fractional distillation (2) [20]



QUESTION 2 Consider the following representation of organic molecules A to F listed in the table below:

A O ΙΙ CH3 CH2 C CH CH3 Ι CH3

B

H H H

Ι Ι Ι H ─ C ─ C ─ C ─ H Ι Ι Ι Cℓ Br H

C

H H H H Ι Ι Ι Ι H ─ C ─ C ─ C ─ C ─ H Ι Ι Ι Ι H H H H

D

Methanal

E

2-methylhex-3-yne

F

CH3 Ι CH3 ─ C ─ CH3 Ι O Ι H

2.1 Write down the letter that represents a compound that: 2.1.1 Is an aldehyde (1)

2.1.2 Is a saturated hydrocarbon (1) 2.1.3 Has a general formula CnH2n-2 (1)

2.2 Write down the homologous series to which each of the following compounds belongs:

2.2.1 A (1) 2.2.2 B (1) 2.2.3 F (1)

2.3 Write down the:

2.3.1 Molecular formula of the next compound in the same homologous series as compound C. (1) 2.3.2 Structural formula of compound E (2) 2.3.3 IUPAC name of compound B (2) 2.3.4 Functional group of compound D (1)

[12]

─ ─ ─ ─



QUESTION 3 Two compounds A and B, have the molecular formula C2H4O2. 3.1 What is meant by the term structural isomers ? (2) 3.2 Compound A has a lower vapour pressure than compound B. 3.2.1 How will the boiling point of compound A compare to that of compound B. Only write HIGHER THAN, LOWER THAN, or EQUAL TO. (1) 3.2.2 Write down the name of compound A. (1) 3.2.3 To which class of organic compound does compound B belong? (1) 3.2.4 Write down the structural formula for compound B and give its IUPAC name. (3) 3.2.5 Explain in terms of intermolecular forces and energy why compound A has a lower vapour pressure than compound B. (3) [11]



QUESTION 4 Consider the following sequence of organic reactions and then answer the questions that follow. Reactions are labeled from I to VI while organic compounds are labeled from A to D. 4.1 Give the reagent needed for each of the following reactions:

4.1.1 Reaction III (1)

4.1.2 Reaction V (1) 4.2 Compound A is a major product of reaction IV. 4.2.1 Name the type of reaction that takes place. (1) 4.2.2 Write down the structural formula of compound A. (2) 4.3 Reaction II converts compound A to compound B in the presence of concentrated sulphuric acid. 4.3.1 Is compound A a PRIMARY, SECONDARY or TERTIARY alcohol? (1) 4.3.2 Name the type of reaction that takes place. (1) 4.4 Reaction I is a combustion reaction. 4.4.1 Write down the balanced chemical equation for this reaction. (2) 4.4.2 Eleven grams (11g) of C3H8 undergoes complete combustion. Determine the mass of CO2 gas produced at STP. (4) [13]

C3H6

B

CH3CHCℓCH3 D

CO2 + H2O

C3H8O A

C3H8

C

II

IV

V VI

I

III



QUESTION 5 A manufacturer makes a polymer, polyethene from the monomer, ethene by means of addition polymerisation. The polymer produced has an average relative molecular mass of 1,0 x 104.

5.1 What is meant by the following terms?

5.1.1 monomer (2)

5.1.2 polymerisation (2) 5.2 Write down an equation for the polymerisation of ethene to produce polyethene. (3) 5.3 How many monomer units are joined together to give polyethene with a relative molecular mass of 1.0 x 104? (2) 5.4 Most plastic bags are made from polyethene. Give one negative impact of the use of plastics on the environment. (1)

[10]



QUESTION 6 (Start on a new page.) A group of learners conduct an experiment to investigate the rate of a reaction. The learners use a small amount of granulated zinc which is added to excess hydrochloric acid.

The balanced equation for the reaction is as follows:

Zn (s) + 2HCℓ (aq) → ZnCℓ2 (aq) + H2 (g)

The hydrogen gas produced is collected at 290K. By measuring the volume

of gas produced as a function of time, the graph below was obtained.

6.1 What information does the gradient of this graph give? (2) 6.2 Describe how the gradient of this graph changes between t=100s and t=200s? Give a reason for your answer. (2) 6.3 Give a reason why the graph becomes flat after 300 seconds? (2) 6.4 Calculate the average rate of reaction in cm3

·s-1 for the first 100s. (3) 6.5 Use the collision theory to explain how the rate of the above reaction will change when the temperature is increased from 290K to 313K. (3) 6.6 The gas liberated in this experiment was collected at STP. Calculate the mass of zinc that was used. (5)

[17]

Vol

ume

H2(

cm3 )

Time (s)



QUESTION 7 The Haber process is represented by the equation below:

N2(g) + 3H2(g) ⇌ 2NH3(g) ∆H < 0 7.1 The percentage yield of ammonia increases with an increase in pressure at a a given temperature. Give a reason for this. A mixture of nitrogen with an initial concentration 0,50 mol.dm-3 and hydrogen with an initial concentration 1,50 mol.dm-3 are placed in a closed 1 dm-3 container. When the equilibrium is attained at a certain temperature, 25,0% of the original nitrogen is consumed (used up). 7.2 Calculate the value of the equilibrium constant (Kc) under these conditions. (8) 7.3 How will the value of Kc change when: 7.3.1 Some NH3 is pumped into the container? (1) 7.3.2 The temperature has been increased? (1) (Write only INCREASES; DECREASES or STAYS THE SAME) [12]



QUESTION 8 Commercial vinegar contains a small percentage of ethanoic acid. A laboratory technician wishes to determine the concentration of ethanoic acid in vinegar. He titrates a solution of ethanoic acid against a standard solution of sodium hydroxide of concentration 0,009 mol.dm–3. The equation for the reaction is:

CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(aq)

The apparatus shown below was used during the titration.

25,00 cm3 of vinegar was diluted with distilled water and made up to a volume of 250,00 cm3. Some of the diluted solution was added to apparatus B. 25,00 cm3 of sodium hydroxide solution was added to apparatus C and few drops of an indicator added. 8.1 What is the name of apparatus B? (1) 8.2 Ethanoic is considered a weak acid. What is meant by term ‘weak acid’? (2) A titration was carried out and the results tabulated as shown below:

Experiment Volume of CH3COOH (cm3)

1 21,1

2 21,1

3 20,9

8.3 What observation is made to identify the end point for the acid-base titration? (1)



8.4 Which one of the indicators listed in the table below is suitable to be used for the above titration? Give a reason for the answer. (3)

Indicator pH range

Methyl orange 2,9 – 4,0

Bromothymol blue 6,0 – 7,6

Phenolphthalein 8,3 – 10,0

8.5 Calculate the concentration of dilute ethanoic acid. (5) 8.6 Calculate the concentration of ethanoic acid in vinegar. (4)

[16]



QUESTION 9 A grade 12 learner finds a 250cm3 sulphuric acid (H2SO4) solution bottle with the following information and hazard symbol:

pH = 2,2

9.1 Suggest ONE safety precaution that should be taken when using the sulphuric acid in the experiment. (2) 9.2 Calculate the concentration of the sulphuric acid solution in the bottle. (6)

[8] QUESTION 10 A galvanic cell is set up with Aℓ / Aℓ 3+ (aq) and Pt / Cℓ2/ Cℓ

-(aq) half cells under standard conditions as shown below.

10.1 State the standard conditions that apply to this cell. (3) 10.2 Is Aℓ the anode or cathode? Give a reason for the answer. (2) 10.3 How will the mass of aluminium electrode change while the cell is in operation? (Write only INCREASES, DECREASES or STAYS THE SAME). (1) 10.4 Write a half reaction to support the answer in 10.3 above. (2)

Aℓ(s) Cℓ2(g)

Pt(s)



10.5 Write down the:

10.5.1 Formula of the oxidizing agent in this cell. (1)

10.5.2 Reduction half reaction (2)

10.5.3 Overall net cell reaction (3)

10.6 Calculate the initial emf of the cell. (4)

[18]

QUESTION 11 A 50 kg bag of fertilizer contains some information as shown below:

11.1 What information is represented by the numbers 3:2:5 (26) printed on the bag. (3)

11.2 Calculate the percentage of nitrogen in this bag. (2)

11.3 Is this fertiliser suitable for growing tomatoes? Give a reason for your answer. (2)

11.4 A member of a community came across a dam near the farm and saw the dam with a thick green covering on it. According to the community member the area was filled with a stench that was unbearable. The community member also noticed rotten fish floating on the surface.

11.4.1 NAME the phenomenon taking place in the dam. (2) 11.4.2 State a possible cause of the phenomenon in 11.4.1 (2) 11.4.3 Suggest TWO possible ways to prevent the phenomenon named in 11.4.1 from occurring. (2)

[13] TOTAL MARKS: 150

basic education - smartlearner the diagram below represents a part of an electrochemical cell used...

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