chemistry/cechemistry/internal exam... · web viewdirections: each question below (question number...

Class: F.5____ ( ) Baptist Lui Ming Choi Secondary SchoolFirst Term Examination (201 2 -201 3 ) Date: 06-12-2012

Name: _____________ F.5 Chemistry Time: 10:40–12:40

1. ANSWER ALL QUESTIONS.

2. Answers to Section A should be marked on the Multiple-choice Answer Sheet while answers to

Section B should be written in the spaces provided in Question-Answer Book B.

3. Atomic numbers and relative atomic masses of elements can be obtained from the Periodic Table

printed on last page.

Section A: Multiple Choices (30%)

1.

Which of the following substances are acidic?

(1) Milk (2) Window cleaner (3) Orange juiceA. (1) and (2) B. (1) and (3) C. (2) and (3) D. (1), (2) and (3)

2.

Which of the following chemical species are present in an aqueous potassium hydroxide solution?

(1) KOH(aq) (2) K+(aq) (3) OH-(aq) (4) H2O(l)A. (1) and (4) B. (1), (2) and (3) C. (2), (3) and (4) D. (1), (2), (3) and (4).

3.

Which of the following substances has a pH value below 7?

A. baking powderB. vinegarC. milk of magnesiaD. drain cleaner

4.

Given that the pH value of a sulphuric acid solution, H2SO4(aq) is 1.70. Calculate the concentration of the acid solution.A. 0.01 M B. 0.02 M C. 0.04 M D. 5 x 10-4 M

5.

Which of the following statements is INCORRECT?

A. A strong acid is fully ionized in its aqueous solution.B. A weak acid is a solution of low concentration.C. Aqueous ammonia solution is a weak alkali.

D. Iron(II) hydroxide is dirty green in colour.

P.T.O.Form 5 Chemistry P.2

6. The pH values of a hydrochloric acid solution and an ethanoic acid solution are equal to 2.0. It can be concluded thatA. they have the same concentration.B. they have the same solution volume.C. they have the same strength.D. they have the same concentration of hydrogen ions.

7. Which of the following methods can be used to produce zinc chloride?(1) Add excess zinc to dilute hydrochloric acid.(2) Add excess zinc oxide to dilute hydrochloric acid.(3) Mixing equal volume of 1M zinc nitrate solution to 1M magnesium chloride solution.

A. (1) and (2) B. (1) and (3) C. (2) and (3) D. (1), (2) and (3)

8. When sodium hydroxide is added slowly to a beaker of hydrochloric acid,(1) the pH of the solution decreases.(2) the temperature of the solution increases and then drops.(3) the conductivity of the solution changes.


9. Acidic wastewater discharged from electroplating factories causes water pollution. Which of the following solutions could be added to the wastewater to prevent water pollution?A. sodium chlorideB. sulphur dioxideC. sodium hydrogensulphateD. calcium hydroxide

10.

Which of the following combinations about the use of oil fraction is correct?

A B C DFraction Refinery gas Gasoline Kerosene DieselUse Making lubricant As fuel for cars Surfacing roads As fuel for cooking

11.

Polypropene and propene

A. have the same molecular formula.B. belong to the same homologous series.C. have different properties.D. have unsaturated structures.

To be continuedForm 5 Chemistry P.3

Direction: Question 12 – 13 refer to the following information:Acid X is a weak acid. It has the formula H6C2O6. 5.04g of acid X crystal was dissolved in distilled water to make up 250.0 cm3 solution. 25.00 cm3 of the solution required 26.60 cm3 of 0.30M sodium hydroxide solution for complete neutralization.

12.

What is the molarity of acid X solution?

A. 0.04M B. 0.16M C. 0.24M D. 0.32M

13.

What is the basicity of acid X?

A. 6 B. 4 C. 3 D. 2

14.

The table below gives the boiling point ranges of four fractions that are found in petroleum.Fraction 1 2 3 4

Boiling point range

Room temp -100oC

100 – 150oC 150 – 200oC 200 – 250oC

Which of the following statements is correct?A. Viscosity decreases from fraction 1 to fraction 4.B. Fraction 3 evaporates more easily than fraction 2.C. Fraction 1 burns with a very sooty flame.D. All fractions are mixture of hydrocarbons.

15.

Which of the following pairs of substances, when mixed, would undergo a chemical reaction?

(1) Bromine water and sodium sulphite solution(2) Calcium chloride solution and magnesium nitrate solution(3) Zinc nitrate solution and sodium hydroxide solution


16.

The oxidation number of copper in [Cu(NH3)4] 2+ is

A. –2 B. +2 C. 0 D. +4

17.

Fractional distillation of crude oil involves

(1) physical separation.(2) chemical decomposition.(3) redox changes.

Which of the following is correct?A. (1) only B. (2) only C. (2) and (3) only D. (1), (2) and (3)


18.

Part of a polymer molecule is shown below:CHClCH2CHClCH2CHClCH2

Which of the following is the molecular formula of its monomer?A. C2H4 B. C3H2Cl2 C. C2H3Cl D. C3H5Cl

19.

Which of the following statements about addition polymerization are correct?(1) It is a chemical reaction.(2) The monomer molecules involved must contain unsaturated carbon-carbon bonds.(3) Small molecules would not be eliminated in the process.A. (1) and (2) B. (1) and (3) C. (2) and (3) D. (1), (2) and (3)

20.

Which of the following hydrocarbons can be polymerized?

A. C2H6 B. C3H8 C. C4H8 D. C4H10

21.

Which of the following might be the respective relative molecular masses of four consecutive members of a homologous series?A. 32, 46, 60, 74B. 26, 38, 50, 62C. 28, 38, 48, 58D. 44, 57, 70, 83

22.

Which of the following building materials is most easily damaged by acid rain?

A. Sandstone B. Limestone C. Concrete D. Brick

23 Which of the following are NOT rechargeable cells?

.A. Nickel-metal hydride cellsB. Lithium-ion cellsC. Hydrogen-oxygen fuel cellsD. Lead-acid accumulators

24.

Which of the following substances can react with acidified potassium permanganate solution?(1) Propene (2) Sodium sulphate solution (3) Potassium iodide solution


25.

When a solution containing sodium nitrate and copper(II) sulphate is electrolysed with graphite electrodes, which element is formed at the anode?A. Copper B. Nitrogen C. Sulphur D. Oxygen


Directions: Each question below (Question number 26 to 30) consists of two separate statements. Decide whether each of the two statements is true or false; if both are true, then decide whether or not the second statement is a correct explanation of the first statement. Then select one option from A to D according to the following table:

A. Both statements are true and the 2nd statement is a correct explanation of the 1st statement.B. Both statements are true but the 2nd statement is NOT a correct explanation of the 1st

statement.C. Only one statement is true while the other is false.D. Both statements are false.

1 st statement 2 nd statement

26. An unused zinc-carbon cell will become useless after a few years.

The electrolyte can slowly react with other chemicals inside a cell.

27. Bromine in an organic solvent reacts with hexane in the presence of sunlight.

The reaction between bromine in an organic solvent and hexane is a substitution reaction.

28. CH3CH2CH2CH2OH and CH3CH2COOH belong to the same homologous series.

Both CH3CH2CH2CH2OH and CH3CH2COOH have the same functional group OH.

29. Conical flask used in titration must be dried before use.

The presence of water inside the conical flask will dilute the solution added.

30. All metal hydroxides are alkalis. All metal hydroxides are soluble in water.

END OF SECTION A

Class: F.5_____ ( ) Baptist Lui Ming Choi Secondary School Mark: _________First Term Examination (2012-2013) Date: 06-12-2012

Name:_______________ Form 5 Chemistry Time: 10:40–12:40

SECTION B: Question-Answer Book (70%)

1. Chemists standardize sodium hydroxide solutions using the potassium hydrogenphthalate (KHC8H4O4) as a primary standard. A 25.00 cm3 sample of a sodium hydroxide solution requires 23.10 cm3 of 0.0994 M potassium hydrogenphthalate solution for complete reaction.

KHC8H4O4(aq) + NaOH(aq) KNaC8H4O4(aq) + H2O(l)(a) (i) What is a standard solution?

(ii) State a characteristic property of an acid-alkali standard material.

(iii) What is the basicity of potassium hydrogenphthalate? Explain.

(iv) Besides potassium hydrogenphthalate, suggest another standard material for acid and alkali titration.

(v) Why does a solution of sodium hydroxide need to be standardized? Give a reason.

(5%)(b)

(i) Name the apparatus necessary to measure the 25.00 cm3 sample of sodium hydroxide solution.

(ii) Given that potassium hydrogenphthalate is a weakly acidic substance. Suggest a suitable indicator for the titration and state the end-point colour change of the titration.

(iii) Calculate the concentration of the sodium hydroxide solution.

(5%)


2. A sample of nickel(II) sulphate (NiSO4) was made by reacting nickel(II) oxide (NiO), an insoluble base, with an acid. The acid was warmed in a beaker and nickel(II) oxide added until there was left over excess nickel(II) oxide in the beaker. The mixture was filtered giving a green solution. The green solution was partly evaporated (by boiling) and then left to cool for a few hours. Finally, nickel(II) sulphate crystal is obtained from its saturated solution.(a) (i) What is meant by neutralization?

(ii) Which acid would have been used to make nickel(II) sulphate?

(iii) Write a chemical equation for the formation of nickel(II) sulphate.

(iv) Write an ionic equation for the reaction between nickel(II) oxide and the acid.

(4%)(b)

(i) Why was excess nickel(II) oxide added?

(ii) Why was the acid – nickel(II) oxide mixture warmed?

(iii) Why was the acid – nickel(II) oxide mixture filtered?

(iv) Suggest the colour of nickel(II) ions in aqueous solution.

(v) Describe how do you obtain nickel(II) sulphate crystal from its saturated solution.

(6%)To be continued

Form 5 Chemistry P.3

3. Crude oil is a mixture consisting mainly of hydrocarbons. Different petroleum fractions can be separated from crude oil by suitable method. The table below lists the length of carbon chain of the hydrocarbons in some of the fractions.Fraction Petrol/ Naphtha Kerosene Diesel XLength of carbon chain C5 – C10 C11 – C18 C18 – C25 C20 – C34

(a) (i) State the industrial method that can be used to separate different fractions from crude oil.

(ii) State the relationship between length of carbon chain to a physical property of the fractions.

(iii) Describe the principle underlying the separation method of crude oil.

(4%)(b)

(i) State ONE use of kerosene.

rocksil soaked with liquid paraffin

broken pieces of unglazed porcelain

heatgaseous products obtained from cracking

water

(ii) Explain why the global demand for petrol is greater than that for kerosene.

(2%)(c) In Hong Kong, naphtha instead of coal is used to manufacture town gas.

(i) Explain why an additive with a foul smell is added to town gas before it is delivered to the consumers.

(ii) State ONE advantage of using naphtha instead of coal to manufacture town gas.(You are NOT required to consider the price of the materials.)

(3%)(d)

Give ONE use of fraction X in cars.

(1%)P.T.O.


4. A student carried out the process of cracking in the laboratory.(a) The student ignited medicinal paraffin with a burning splint. Briefly describe the flame

produced. (Hint: flame colour and sootiness must be mentioned.)

(2%)(b)

Medicinal paraffin was cracked by using the set-up shown below.

(i) State the function of broken pieces of unglazed porcelain in the cracking process.

pure copper electrode

copper(II) sulphate solution

impure copper electrode

(ii) Suggest ONE substances which could replace the broken pieces of unglazed porcelain in the above set-up.

(iii) Why is the first few cm3 of gas coming out of the reaction tube is not collected?

(iv) State the importance of cracking.

(v) One of the gaseous products collected after the process reacts with bromine (dissolved in organic solvent) in darkness. What would be observed when the gas is shaken with bromine solution?

(vi) Before stopping the heating, what safety precautions should be taken? Why?

(8%)To be continued


5. The diagram below shows the refining of copper by electrolysis.

(a) Explain why copper(II) sulphate solution can conduct electricity.

(1%)(b)

Which species are preferentially discharged at the anode and cathode respectively? Explain your answer briefly.

water out

water in

A

a solution of styrene in keroseneanti-bumping granule

heat

(4%)(c) What is the change in colour intensity of the copper(II) sulphate solution? Explain your

answer briefly.

(3%)(d)

Sate TWO observable changes if the impure copper electrode is replaced by a graphite electrode.

(2%)


6. (a) Polystyrene can be produced by the set-up shown below.

digital multimeter (as voltmeter)

copper electrode

X

copper(II) sulphate solution

iron(II) sulphate solution

iron can

(i) State the function of kerosene in this experiment.

(ii) State the function of apparatus A.

(iii) Write chemical equation for the reaction occurred.

(iv) Explain whether polystyrene is suitable for making(1) electrical sockets.

(2) foam cups for hot drinks.

(5%)


6. (b)

A student built a simple chemical cell as shown below.

(i) What is X? State the functions of X.

(ii) What is the direction of electron flow in the external circuit of the cell? Why?

(iii) Explain what happens to the voltmeter reading if the copper electrode is replaced by a silver electrode.

(5%)

7. (a) (i) Suggest ONE method to determine the pH of an aqueous solution.

(ii) 5.00 dm3 of a solution contain 0.245 g of sulphuric acid. Assuming complete ionization, calculate the pH of this solution.


7. (a) (iii) Arrange the following substances in order of increasing pH and explain your answer.2M ethanoic acid, 2M hydrochloric acid, 2M sulphuric acid

(6%)(b Study the following reaction scheme of metal A.

)

(i) Give the names of A and E.

(ii) Write an ionic equation for the reaction between solution C and dilute sodium hydroxide solution.

(iii) A student concluded that “concentrated nitric acid is a strong acid which reacts with metal A to form salt and hydrogen ”. Do you agree? Given your comment.

(4%)END OF PAPER

Baptist Lui Ming Choi Secondary SchoolFirst Term Examination (201 2 -201 3 )

F.5 Chemistry Suggested Answers

SECTION A: Multiple Choices (30%)1 2 3 4 5 6 7 8 9 10

0 B C B A B D A C D B1 C B D D B B A C D C2 A B C B D A B D C D

SECTION B: Question-Answer Book (70%)

1. (a) (i) A standard solution is a solution with accurately known molarity . [1](ii) High purity/ chemically stable/ easily dissolved in water/ involatile/ not hygroscopic

(absorb moisture from air) (any ONE) [1](iii) It is monobasic (or its basicity is one). Since one mole potassium hydrogenphthalate

reacts with one mole sodium hydroxide. [1](iv) Anhydrous sodium carbonate/ ethanedioic acid crystal (any one) [1](v) It absorbs carbon dioxide from the air. [1]

(b)

(i) Pipette. [1]

(ii) Phenolphthalein. [1]End point colour change: from pink to colourless [1]

(iii) No. of mole of KHC8H4O4 used = 0.0994 M x 23.1 x 10-3 dm3 = 2.296 x 10-3 mol [1]KHC8H4O4(aq) + NaOH(aq) KNaC8H4O4(aq) + H2O(l)No. of mole of NaOH reacted = 2.296 x 10-3 molMolarity of NaOH = 2.296 x 10-4 mol / 25 x 10-3 dm3 = 0.0918 M// [1]

2. (a) (i) Neutralization is a reaction between acid and alkali (or base) to form salt and water only. [1]

(ii) Sulphuric acid (or H2SO4) [1](iii) H2SO4(aq) + NiO(s) NiSO4(aq) + H2O(l) [1](iv) 2H+(aq) + NiO(s) Ni2+(aq) + H2O(l) [1]

(b)

(i) To ensure that all sulphuric acid have been reacted [1].

(ii) To speed up the reaction between sulphuric acid and nickel(II) oxide [1].(iii) To remove unreacted (or excess) nickel(II) oxide from the nickel(II) sulphate solution.

[1](iv) Green [1].(v) Procedure of crystallization. [1]

The crystals of nickel(II) sulphate were filtered off [1]Washed with little distilled water / dried with filter paper. [1] (Any TWO)


3. (a) (i) Fractional distillation of crude oil [1].(ii) Longer the length of carbon chain, higher the boiling point ranges of/ viscosity of/

colour intensity of/ sootiness when burning/ difficulty to ignite (or lower volatility of) the fractions. [1]

(iii) Different fractions have different boiling point ranges [1].Vapour of hydrocarbons with lower molecular mass condenses at lower temperature/ Vapour of hydrocarbons with higher molecular mass condenses at higher temperature [1]

(b (i) It acts as a fuel for jet plane / household fuel [1].

)(ii) The rapid growth in the number of motor cars makes the demand of petrol much

greater than that of kerosene. [1](c) (i) Because town gas contains carbon monoxide which is highly toxic (or hydrogen

which is explosive) [1], so an additive is added to alert the consumers of leakage of town gas [1].

(ii) Using naphtha give less air pollution than using coal. [1](d)

It can be used as a lubricant (or lubricating oil) for motor cars. [1]

4. (a) The flame is orange/yellow [1] and sooty[1].(b)

(i) It acts as a catalyst to speed up the reaction. [1]

(ii) Broken pieces of porous pot [1] / aluminium oxide / pumice stone(iii) It is because it is mainly air expelled from the reaction tube. [1](iv) To produce extra petrol[1] and alkene[1].(v) Bromine turns from yellow to colourless.[1](vi) The student should remove the delivery tube from water before stopping the

heating. [1] This prevents sucking back of water which may crack the hot combustion tube. [1]

5. (a) It is because it contains mobile ions.[1](b)

At the anode, copper is preferentially discharged [1] because copper is a stronger reducing agent than hydroxide ion. [1]At the cathode, copper(II) ion is preferentially discharged [1] because copper(II) ion is a stronger oxidizing agent than hydrogen ion. [1]

(c) There is no change in colour intensity of the copper(II) sulphate solution. [1] It is because for every Cu2+(aq) ion discharged at the cathode, one is formed at the anode. [1] Therefore, the concentration of copper(II) sulphate solution remains unchanged. [1]

(d)

Some colourless gas bubbles would be observed at the graphite electrode. [1]The blue colour of the solution would become paler. [1]


6. (a) (i) It acts as a solvent / catalyst[1].(ii) It is used to condense vapour formed from the mixture during heating, thus

preventing the escape of vapour. [1](iii)

[1]

(iv) (1) Polystyrene is not suitable for making electrical sockets as it is easily softened and deformed under high temperatures. [1]

(2) Expanded polystyrene is suitable for making foam cups as it is a good heat insulator and non-poisonous. [1]

(b)

(i) X is a porous pot. [1] It is used to complete the circuit.[1]

(ii) From iron can to copper electrode. [1]It is because iron is more reactive than copper. [1]

(iii) The voltage reading measured would be greater.It is because the difference in reactivity between iron and silver is greater than that between iron and copper. [1]

7. (a) (i) Using pH meter. [1](ii) No. of mole of H2SO4 = 0.245/ (2 x 1 + 32.1 + 4 x 16) = 2.497 x 10-3 mol

Concentration of H2SO4 = 2.497 x 10-3 mol / 5 dm3 = 4.995 x 10-4 M [1]Concentration of H+ = 2 x 4.995 x 10-4 = 9.90 x 10-4 MpH = -log [H+] = -log (9.90x10-4) = 3.00// [1]

(iii) pH value: 2M sulphuric acid < 2M hydrochloric acid < 2M ethanoic acid [1]Since ethanoic acid is a weak acid which is slightly ionized in water, but both hydrochloric acid and sulphuric acid are strong acid that are completely ionized in water, hence pH value of ethanoic acid is higher than that of both hydrochloric acid and sulphuric acid [1]. Since hydrochloric acid is a monobasic acid but sulphuric acid is dibasic acid,hence the pH value of hydrochloric acid is higher than that of sulphuric acid [1].

(b)

(i) A is copper and E is copper(II) hydroxide. [1+1]

(ii) Cu2+(aq) + 2 OH-(aq) Cu(OH)2(s) [1](iii) No. Because ordinary acid does not react with copper metal which is a not reactive

metal [1]. (or Acid reacts with metal to give hydrogen which is colourless. However, concentrated nitric acid reacts with copper to give a brown gas. This means concentrated nitric acid does not behave as an ordinary acid)

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