Hkcee Chem Samuel 1 e Ans

8/10/2019 Hkcee Chem Samuel 1 e Ans

1/11

CE Chemistry

Paper I Marking Schemes

Dr. Samuel Chong

Dr. Samuel Chong

AB C 04 05 (SWA)

05 06


2/11

By Dr. Samuel Chong Chemistry Team 1

Marks

1. (a) (i) calcium carbonate

(ii) gas bubbles are given off.

(b) (i) Compound A calcium oxide ; Gas B carbon dioxide

(ii) Brick-red colour

(iii) Test the gas B with limewater which will turns milky.

(c) calcium hydroxide

It is used to neutralize the acidity of soil.

1

1

1,1

1

1

1

1

(8)

2. (a) There is strong covalent bond between oxygen atoms.

There is weak van der Waals force between oxygen molecules

(b)(i) Fractional distillation

(ii) The liquefied gases is separated by fractionating column under different

boiling points.

(c) No, it is not a good conductor of electricity.It is because there is no mobile electrons or ions.

1

1

1

1

1

1

(6)


3/11


Marks

3. (a) Add both concentrated sulphuric acid and concentrated nitric acid to copper.

Concentrated nitric acid gives reddish-brown gas while concentrated

sulphuric acid does not.

(b) Bromine in tetrachloromethane is added to both propene and propan-1-ol.

Propene decolourize bromine while propan-1-ol cannot.

1

1

1

1

(4)

4. (a) Zinc sulphate crystals cannot conduct electricity because there is no mobile

ions.

(b)(i) P, hydrogen

(ii) The gas burns with a pop sound with a burning splint.

(iii) The zinc electrode dissolves gradually.

(c) Valid. Bromine gas liberating in cell B is toxic.

1

1+1

1

1

1

(6)


4/11


Marks

5. (a) adding an alkaline solution / sodium hydroxide solution / ammonia

solution into sewage and filter the precipitate

Cu2++ 2OH- Cu(OH)2

(b) Soapy detergent can be precipitated by adding solution containing

calcium ion / magnesium ions / hard water, then remove the white solid

(scum) by filtration.

(c) Incineration / burning of polystyrene waste.

This will greatly reduce the volume of the waste. Or

Recycling of polystyrene waste. This can save petroleum.

1

1

1

1

1

1

(6)


5/11


6/11


Marks

8. First, adding bromine water to all samples, the one

decolorizing bromine is sodium sulphite,

the one forming a darker brown solution is sodium iodide.

Others have no observable change.

Then adding red dye solution to the three remaining samples, the one

decolorizing the dye is sodium hypochlorite. Others have no observable

change.

Afterwards, adding dilute HCl to the two remaining samples, the one

giving out a colourless gas is sodium carbonate. Other has no observable

change.

Finally, the remaining sample is sodium sulphate.

1

1

1

1

1+1

(6)


7/11


Marks

9. (a) (i) 4NH3(g) + 3O2(g) 2N2(g) + 6H2O(l)

(ii) It is reducing agent because the oxidation number of N increase

from -3 to 0.

(iii) According to the equation in (a),

the mole ratio of NH3to O2= 4 : 3

Hence, oxygen is in excess.

According to the equation in (a),

the mole ratio of NH3to N2= 2 : 1

Hence, number of moles of nitrogen formed = 0.4 / 2 = 0.2 mol

Mass of nitrogen formed = 0.2 (14 2) = 5.6 g

(b) (i)Place about 2 cm3of each acid in separate test tubes. Add a few drops of

silver nitrate solution to each test tube. A white precipitate will be

observed in the test tube containing hydrochloric acid.

(ii) Dilute hydrochloric acid is a strong acid and ethanoic acid is a weakacid. Dilute hydrochloric acid dissociates fully in water whereas

ethanoic acid dissociates partially in water to form less hydrogen ions,

H+(aq).

1

1,1

1

1

1

1

1

1

(9)


8/11


Marks

10. (a) (i)

I: anti-bumping granules

II: direction of water in condenser

III: cold water bath

(ii) Provide a large surface area for condensation and vapourization of the mixture

(iii) When hex-l-ene is added, addition reaction occurs and all hex-l-ene are used

up. Since addition reaction cannot be reversed by heating, hex-l-ene will not

be found in the distillate

1

1

1

1

1

1

(6)


9/11


(b)

(-1 for wrong method to collect the product)

(-1 for no catalyst)

(-1 for heating decane directing)

The porcelain is heated strongly in the absence of air.

The gaseous products are collected by displacement of water

1

1

1

(3)


10/11


C H2O

C HO

C H2O

C

C

C

O

O

O

( C H2) 16C H3

( C H2) 16C H3

( C H2) 16C H3

C H2O H

CHOH

C H2O H

3 C H 3( CH2) 1 6 COO-Na3 Na OH+ +

11. (a)

(b) The hydrocarbon tail is hydrophobic which is readily soluble in the greasy

dirt.

The COO(ionic) end is hydrophilic which is readily soluble in water.

Agitation will cause the grease to break down into droplets.

The negative charge on the droplets repels each other and emulsion isformed.

(c) No, I do not agree.

Hard water contains Ca2+or Mg2+ions .

Soaps react with Ca2+or Mg2+ions to form scum which is difficult to

remove.

Soapless detergent reacts with Ca2+or Mg2+ions to form no scum.

2

1

11

1

1

1

1

(1)

(9)

+


11/11


Marks

12. Wash a 25.0cm3pipette with distilled water and sodium carbonate solution.

Transfer 25.0 cm3of sodium carbonate solution to a clean conical flask with the

pipette and add a few drops of methyl orange.

Wash the burette with distilled water and nitric acid before filling it with the acid.

Put a white tile under the conical flask and run the acid from the burette until there

is colour change.

Record the volume of nitric acid added and repeat the titration 2 or 3 times for

accurate result.

Calculation of the molarity of the sample of sodium carbonate solution:

Na2CO3 + 2 HNO32NaNO3+ CO2+ H2O

Number of moles of HNO3(aq) = average volume of HNO3(aq) used

concentration of HNO3(aq)

Number of moles of Na2CO3(aq) = number of moles of HNO3(aq) 2

Volume of Na2CO3(aq) molarity of Na2CO3(aq) = Number of moles of

Na2CO3(aq)

Effective Communication

1

1

1

1

1

1

3

Hkcee Chem Samuel 1 e Ans

Documents

Transcript of Hkcee Chem Samuel 1 e Ans