2012 4E P2 Chem(SPA) MY final.doc

7/27/2019 2012 4E P2 Chem(SPA) MY final.doc

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Answerall questions in this section in the spaces provided.

The total mark for this section is 50.

A1 The box below lists some common gases.

sulfur dioxide nitrogen

ammonia oxygen

chlorine carbon dioxide

Use the words above to answer the following questions.

Each word can be used once, more than once or not at all.

Name a gas which:(a) dissolves in water to form an alkaline solution,

(b) is necessary for combustion to take place,

(c) exists as diatomic molecules,

(d) turns acidified potassium dichromate(VI) solution from orange to green,

[4]

(e) Six identical jars are filled with the same volume of these six gases,measured at room temperature and pressure. The lids were removed and thejars were left undisturbed for several hours. [2]

(i) State and explain which jar would contain the least air in it.

(ii) Suggest a test you can perform in the science laboratory to confirmyour answer in (i). Write down the observations you expect to make. [2]


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[Total:8 marks]

A2 Ozone is a more powerful oxidizing agent than oxygen. It will oxidize lead(II)

sulphide (PbS) to form lead(II) sulfate and oxygen. Write an equation, with statesymbols, for this reaction. Explain the oxidation reaction in terms of oxidationnumber.

Equation

Explanation

[Total:3 marks]

A3 Bottles of aqueous potassium chloride, aqueous potassium bromide and aqueouspotassium iodide were delivered to the science laboratory. However, the bottles werenot labeled. Using chlorine or one other chemical, explain in detail how you wouldidentify the contents of each bottle.

[Total:4 marks]

A4 The table below gives the results of the experiments between three metals andaqueous solutions of their salts.

silver metal X magnesiumaqueous Xsalt

nodisplacement

nodisplacement

displacement


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aqueoussilver salt

nodisplacement

displacement B

aqueousmagnesiumsalt

nodisplacement

A nodisplacement

What would be the result in(a) A

(b) B

(c) The metals in order of increasing reactivity is

[Total: 3 marks]

A5 Arun conducted an experiment to investigate the speed at which magnesium metalreacts with 20 cm3 of hydrochloric acid. The set-up is as shown below. He collectsthe gas evolved with the help of a gas syringe and uses a stopwatch to time the timetaken. He makes sure he cleans the magnesium metal with a piece of sandpaper.After experiment 1, he washed his apparatuses thoroughly before conductingexperiment 2.He conducted experiment 2 under the same conditions except for using a highervolume of acid.

His results are:

Mass ofmagnesium /g

Concentration ofhydrochloric acid /

mol/dm3

Time taken/s

Experiment x 1.0 45


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1

Experiment2

x 2.0 60

(a) Suggest why is it necessary to clean the magnesium metal with a piece ofsandpaper.

_______________________________________________________________

____________________________________________________________ [1]

(b) Suggest how Arun would know that the reaction is completed.

[1]

(c) Sketch a graph below to represent the time taken against the volume of gasgiven off in experiment 1.

[1]

(d) The experimental values of experiment 2 did not tally with the expected

theoretical values. Suggest one possible reason for the inaccurateexperimental values.

[1]

(e) (i) Experiment 1 was repeated with the same mass of magnesium. However,the acid was replaced by the same volume and concentration of sulfuricacid. State if the rate of reaction will be faster or slower.

[1]


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(ii) Explain your answer in (d)(i) in terms of reacting particles.

[2][Total:7 marks]

A6 A beaker contains aqueous copper (II) sulfate solution.

Two experiments were performed on two different portions of the solution and theobservations were recorded below.

Write down in the boxes provided, the observations expected in experiments A andB.

Experiment Test Observations

A Excess aqueoussodium hydroxide wasadded.

B A piece of zinc metal

was added intocopper(II) sulfatesolution.

[4]

(a) Write a chemical equation for the reaction in experiment B.

[1]

(b) (i) It was given that the concentration of aqueous copper(II) sulfate solutionis 1.0 mol/dm3 and the mass of zinc metal used was 16.25g.

Calculate the volume of aqueous copper(II) sulfate solution that hasreacted with zinc.


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[2](ii) Calculate the mass of metal deposit formed.

[1]

[Total:8 marks]

A7 Suggest reasons for the following observations.

(a) Magnesium blocks are attached to long underground iron water pipe.

[2]

(b) There is a need to recycle metals.

[2]

(c) It is easier to recycle lead than to recycle aluminium.

[3]

[Total:7 marks]


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A8Chlorofluorocarbons (CFCs) is an air pollutant.

(a) State a source of CFCs.

___________________________________________________________ [1]

(b) Suggest how chlorofluorocarbons (CFCs) form a threat to human beings.

[2]

(c) Difluromethane, CH2F2, is often used as a substitute to chlorofluorocarbons.

Draw a dot and cross diagram to show the bonding in difluromethane. Showonly the valence electrons.

[2]

(d)State two physical properties of Difluromethane.

[2]


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[Total:7 marks]

A9 A hydrocarbon compound is found to have the percentage composition bymass of carbon, 85.7%; hydrogen, 14.3%. What is the empirical formula of thiscompound?

[Total:3 marks]

Section BAnswer all three questions from this section.

Write on the lined pages attached.The last question is in the form either / orand only one of the alternatives should be

attempted.

B10 There are various ways in performing paper chromatography. One common way isthrough the one-way chromatography which we are very familiar with in our school


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science laboratory. It involves separating the components of an unknown sample ina suitable solvent.Another way of performing chromatography is through the two-waychromatography. This is achieved by performing chromatography in a solvent X.After it has dried, the chromatogram was run on a different solvent Y.

The chromatogram below illustrates a mixture of three amino acids separated bytwo-way chromatography. The positions of three spots A, B and C, after treatingwith a locating agent, are indicated in the chromatogram below.

(a) State the formula for the calculation of Rf value. [1]

(b) Suggest why there is a need to use a locating agent here. [1]

(c) Not all unknown substances can be separated using a two way

chromatography. Suggest a criteria for using a two way chromatographymethod.

[1]

(d) Two of the spots (A, B, C) can be identified by the Rfvalues of knownamino acids below.

Amino acid Rf value in solvent X Rfvalue in solvent Y

Glutamicacid

0.38 0.30

Glycine 0.50 0.26

Arginine 0.70 0.20


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Leucine 0.91 0.73

State the identities of two of the spots. [2]

(e) In a similar manner like the values in the table in (d), write down the Rf

values for the unidentified unknown.

[1]

(f) Suggest an advantage of a two-way chromatography method over aone-way chromatography method.

[1]

(g) Paper chromatography proves to be a useful technique to separatecomponents of small amount of unknown mixtures. It also identifies theunknown components of a sample. However, the technique has itslimitations.Suggest one disadvantage of the use of paper chromatography over

other physical separation techniques.

[1]

[Total: 8marks]

B11 Dry ammonia gas reacts with sodium metal to give hydrogen gas and sodamide,NaNH2. It is given that the hydrogen ion in amide ion, NH2

- , has an oxidation stateof -1.

(a) Suggest how you would obtain a dry sample of ammonia gas. [1]

(b) How would you test for the presence of the hydrogen gas formed? Statethe expected results.

[2]

(c) (i) Construct a balanced chemical equation for the reaction betweenammonia and sodium.

[2]

(ii) State if ammonia is oxidised or reduced in this reaction, in terms ofoxidation state.

[2]

(d) In this experiment, 0.78 g of sodamide was obtained.

(i) Calculate the volume of ammonia required for this reaction at r.t.p. [2]

(ii) Calculate the mass of hydrogen gas produced. [1]

(e) Sodium is a very reactive metal which requires proper storage. [2]


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Suggest how you would store sodium metal. State a reason for yoursuggestion.

[Total:12 marks]

EITHER

B12 (a) An experiment was carried out by reacting a few pieces of zinc granuleswith 100 cm3 of sulfuric acid of 1 mol/dm3 concentration. A few crystals ofcopper(II) sulfate were added and the initial rate of evolution of hydrogengas was increased. However, when 5 g of copper(II) sulfate crystal wasadded, the initial rate of evolution of gas did not increase and no moregas were formed after a few minutes.Explain these observations.

[3]

(b) (i) Describe the steps you would take to obtain pure magnesiumchloride crystals from a mixture of solid magnesium chloride andsolid copper(II) carbonate.

[4]

(ii) The mixture in (b)(i) is changed to solid ammonium chloride andsolid copper(II) carbonate. Would the steps taken be different?Explain.

[2]

(c) Suggest two reagents which you can use to form aqueous ammoniumchloride solution.

[1]

[Total:10 marks]

ORB12 (a) The metal iron can be extracted in a blast furnace.

(i) Name the three raw materials that are added into the blast furnace. [1]

(ii) Describe in detail the stages in which the various chemicalreactions take place in the blast furnace up to the formation of ironmetal. Write balanced equations for the reactions.

[4]

(b) Methane reacts with chlorine gas according to the following equation.

CH4(g) + 4Cl2(g) CCl4(g) + 4HCl(g)

The table below shows the bond energies for the chemical bonds measured inkJ/mol.

Bond Bond energy (kJ/mol)

H-Cl 412

C-H 431

C-Cl 338

Cl-Cl 242(i) With the help of the bond energy values listed, calculate the [2]


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overall energy change H for the reaction.

(ii) Is this reaction exothermic or endothermic? [1]

(iii)

In terms of bond breaking and bond making, explain your answerin (b)(ii).

[2]

[Total:10 marks]

End Of Paper

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DATA SHEET

Colours of some common metal hydroxides

aluminium hydroxide white

calcium hydroxide white

copper(II) hydroxide light blue

iron(II) hydroxide green

iron(III) hydroxide red-brown

lead(II) hydroxide white

zinc hydroxide white


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Sec 4E Chemistry(SPA) Prelim P2 2012 FTPSS

Setter: Mrs Ong Siok Lee

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2012 4E P2 Chem(SPA) MY final.doc