O Levels Combined Chemistry G3

O Levels G3 Combined Chemistry Paper 1 mock

Name

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1. In which chemical reaction does the named product have a higher relative molecular mass than the reactant?

the formation of ethanol from glucose

the formation of propene from octane

the formation of carbon dioxide from butane

the formation of dichloromethane from methane

methane CH4 molar mass = 12 +4 = 16g

dichloromethan CH2Cl2 molar mass = 12 +2 + 71 = 85g

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2. Oxygen was prepared and collected using the apparatus as shown in the diagram below.

The first tube of gas collected was discarded as it was contaminated. Which contaminant was in the gas?

hydrogen

hydrogen peroxide

manganese(IV) oxide

nitrogen

There would be air in the test tube and tubing. Thus the main contaminant would be nitrogen gas.

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3. Which diagram best represents the structure of calcium oxide?

A

B

C

D

Ca is cation and O is anion. They are opposite in charge and attract each other. Thus in the diagram, only black balls are bonded to white balls directly.

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4. In which equation does the metal oxide act as an acidic oxide?

K2O (s) + H2O (l) → 2KOH (aq)

Fe2O3 (g) + 3CO (g) → 2Fe (s) + 3CO2 (g)

Al2O3 (s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2O (l)

PbO (s) + H2O (l) + OH− (aq) → Pb(OH)3− (aq)

acidic oxide neutralises base/alkali to form salt and water

CO is neutral.

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5. Which of the following statements about a homologous series is correct?

The melting and boiling point increases with increasing relative molecular mass.

The members have similar physical properties.

The members have the same molecular formula.

The relative molecular masses of consecutive members differ by 12.

The physical properties of members show a trend

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6. The flowchart shows some reactions of a compound T.

What could compound T be?

aluminium carbonate

ammonium nitrate

calcium nitrate

zinc carbonate

Ammonium salt + Strong Alkali --> ammonia gas + water + salt

test for nitrate: add sodium hydroxide solution to the sample, followed by aluminum foil, and gently heat the mixture. If nitrate ions are present, they will be reduced to ammonia gas, which can be detected by its pungent smell or by its ability to turn damp red litmus paper blue.

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7. Which of these Group 1 elements reacts most violently with water?

caesium

lithium

potassium

rubidium

reactivity increases as it goes down the group.

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8. Which of the following statements about isotopes is correct?

sotopes are atoms of the same element with the same number of protons but different number of electrons.

Isotopes are atoms of the same element with the same number of protons but different number of neutrons

Isotopes are atoms of the same element with the same number of neutrons but different number of electrons.

Isotopes are atoms of the same element with the same number of neutrons but different number of protons.

by definition, isotopes are atoms with the same number of protons and diff number of neutrons

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9. When a 10 cm3 sample of a gaseous hydrocarbon was completely burnt in 35 cm3 of oxygen, the total volume of the products formed was 50 cm3.

Which equation represents the combustion of the hydrocarbon?

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g)

Since all the reactants and products are gases, we can use the ratio of volume directly without converting to moles.

10: 35 : 50

2 : 7 : 10

ratio of hydrocarbon is 2, ratio of oxygen is 7 and ratio of the sum of products is 10.

Only D satisfy this ratio

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10. Ammonia and excess carbon dioxide can react to form urea and water in a reaction.

2NH3 + CO2 → CON2H4 + H2O

The percentage yield of this reaction is 80 %.

What is the mass of ammonia required for this reaction to obtain 60.0 g of urea?

[Mr: NH3, 17; CO2, 44; CON2H4, 60; H2O, 18]

10.6 g

27.2 g

34.0 g

42.5 g

Molar mass of urea = 60g --> 1 mole

100/80 x 1 = 1.25 mole of urea

mole of ammonia = 1.25 x 2 = 2.5 mole

mass of ammonia = 2.5 x 17g = 42.5g

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11. Aqueous hydrogen peroxide decomposes to form water and oxygen gas. Two experiments were carried out to measure the rate of production of oxygen from aqueous hydrogen peroxide.

A

B

C

D

Experiment B has more starting reactant but lower concentration than A. Therefore, the curve will be less steep but finish higher.

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12. An impure sample of calcium carbonate with a mass of 1.70 g was reacted with excess hydrochloric acid and 360 cm3 of carbon dioxide was collected at room temperature and pressure. What is the percentage purity of the calcium carbonate?

75%

88%

90%

98%

CaCO3 + 2HCl --> CaCl2 + CO2 + H2O

1 mole --> 24000 cm3

360 cm3 --> 0.015 mole

Ratio of CaCO3 : CO2

1:1

mole of CaCO3 = 0.015 mole

molar mass of CaCO3 = 100g

mass = 0.015 x 100 = 1.5g

% purity = 1.5/1.7 x 100% = 88.2%

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13. A reaction takes place in two stages in the presence of a catalyst:

Which ion is the catalyst in the reaction?

Fe^2+ (aq)

I^– (aq)

SO4^2– (aq)

S2O8^2– (aq)

The catalyst must remain unchanged at the end of the reaction.

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14. Which equations below represent redox reactions?

1. H+ + OH− → H2O

2. MnO4− + 8H+ + 5e− → Mn2+ + 4H2O

3. Cl2 + 2Br −→ Br2 + 2Cl −

1 only

3 only

1 and 2 only

2 and 3 only

neutralisation ( not redox)

redox

redox

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15. A student investigated the diffusion of ammonia gas, NH3, and hydrogen chloride gas, HCl. Two sets of apparatus were set up as shown below at room temperature and pressure.

The damp red litmus paper in apparatus 1 changed colour after 30 seconds. How long does it take for the damp blue litmus paper to change colour in apparatus 2?

about 21 seconds

about 30 seconds

about 64 seconds

The blue litmus paper would not change colour.

Molar mass of ammonia NH3 = 14+3 =17g

molar mass of HCl = 1 +35.5 = 36.5 g

HCl will take longer to diffuse as it has a higher molar mass

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16. Which of the following hydrocarbons would produce the sootiest flame when burnt in air?

CH4

C4H10

C8H18

C12H26

The more C atoms in the molecule, the more soot (unburnt hydrocarbon) will be produced

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17. Which one of the following could be used to distinguish aqueous solutions of sodium chloride and sodium iodide?

aqueous barium chloride

aqueous silver nitrate

aqueous sodium hydroxide

aqueous sulfuric acid

When silver nitrate is added, PPT of silver chloride(white) and silver iodide(yellow) will be formed, respectively

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18. Three elements W, X, Y, and Z have consecutive, increasing proton (atomic) numbers. Element Y exists as a colourless, monatomic gas at room temperature.

Which will be the chemical formula of a compound formed between W and chlorine?

WCl

W2Cl

WCl2

W2Cl3

Y would be noble gas and thus W is in group 16 with 6 valence electrons and need 2 more

Cl has 7 valence and need 1 more so the formula will be WCl2

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19. On adding 50 g of impure limestone, CaCO3 (Mr = 100), to excess hydrochloric acid, 6.0 dm3 of CO2 was evolved at room temperature and pressure.

What is the percentage purity of the limestone?

25%

50%

75%

100%

CaCO3 + 2HCl --> CaCl2 + CO2 + H2O

for CO2:

24dm3 --> 1 mole

6 dm3 --> 0.25 mole

mole ratio of

CO2 : CaCO3

1 : 1

0.25 : 0.25

Molar Mass of CaCO3 = 100g

0.25 mole --> 25g

Therefore, % purity = (25/50) x 100% = 50 %

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20. A warship had its hull plated in copper to protect its wooden hull from rotting. However, after 2 years at sea, it was found that the iron parts of the warship in contact with the copper plates were more corroded than normal. What is the best explanation for this observation?

Copper acts as a catalyst to speed up corrosion.

Copper reacts with the iron to increase corrosion.

Iron displaces copper to form iron(III) oxide.

Iron is more reactive and corrodes in place of copper.

Iron is above copper in the reactivity series. Iron will readily give away electrons to copper. Thus, iron will ionize easily to react with the oxygen in the air to rust.

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