O Levels Combined Chemistry G3

O Levels G3 Combined Chemistry Paper 1 mock

Name

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1. 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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2. Francium, Fr, is an element in the same group of the Periodic Table as lithium, sodium and potassium. Which statement about francium is likely to be correct?

It forms a carbonate Fr2CO3.

It forms coloured compounds.

It reacts slowly with cold water.

It is produced from the electrolysis of aqueous francium chloride.

Use sodium or potassium as guide.

Only extraction with electrolysis is true

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3. The diagram shows the apparatus used to separate hexane (boiling point, 70 oC) and heptane (boiling point, 98 oC).

A

B

C

D

Heptane vapour will condense as it reaches the fractionating column; only hexane vapour will reach the condenser. As the thermometer will only measure the inlet of the condenser, the measured temperature will be constant at the boiling point of hexane until all the hexane has vaporized.

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4. Elements X and Y combine to form an ionic compound. Atoms of X have more protons than atoms of Y.

Atoms of Y have more valence electrons than atoms of X. Which statement is correct?

Ions of X are negatively charged.

Atoms of X have more electron shells than atoms of Y.

X and Y are in the same period of the Periodic Table.

X and Y are in the same group of the Periodic Table.

X and Y, one is metal, one is non-metal.

since Y has more valence then X is metal and Y is non-metal and X has more electron shell since it has protons.

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5. Hydrogen gas reacts with chlorine gas to form hydrogen chloride gas.

H2(g) + Cl2(g) → 2HCl(g)

What is the final volume of the gas mixture when 20 dm3 of hydrogen is reacted with 30 dm3 of chlorine gas at 100 C?

40 dm3

50 dm3

60 dm3

70 dm3

H2(g) + Cl2(g) → 2HCl(g)

hydrogen gas is limiting reagent.

Cl2 gas is excess by 10 dm3

Vol of HCl produced = 2 x 20 dm3 = 40 dm3

Final volume = 40 + 10 = 50 dm3

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6. 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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7. An unknown substance X starts melting at –180 °C and finishes melting at –160 °C. What is substance X likely to be?

a compound

a mixture

an element

insufficient data to determine

Pure compounds and elements will have a fixed melting point. Only mixtures melt over a range

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8. 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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9. How many of the following processes will lead to an increase in greenhouse gas emissions?

1

2

3

4

decomposition -> give out carbon dioxide

fermentation -> give our carbon dioxide

photosynthesis -> take in carbon dioxide

polymerisation -> none, maybe water

respiration -> give out carbon dioxide

neutralisation -> only salt and water

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10. 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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11. The following chemicals are available in the laboratory.

aqueous bromine

Universal Indicator solution

magnesium powder

sodium carbonate

Which of these chemicals can be used to distinguish between propene and propanoic acid?

All of them

1 only

1 and 4 only

1, 2 and 3 only

aqueous bromine --> change colourless/no change

Universal Indicator solution --> turns orange/ green

magnesium powder --> no change/effervescence

sodium carbonate --> no change/effervescence

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12. An element T forms an ion, T2+, which has an electronic arrangement 2.8.8.

Which statement(s) concerning T is/are correct?

I T is an alkali metal.

II T forms a basic oxide with oxygen.

III T is in Period 4 of the Periodic Table.

I and II only

I and III only

II and III only

I , II and III

Since its ion's charge is 2+, it is in group 2 and called Alkali Earth metal not alkali metal.

2,8,8,2 is calcium which is in period 4 as its atom have 4 electron shells.

Its oxide is basic.

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13. When crude oil is fractionally distilled, which list best describes the mixture of compounds collected at the bottom of the fractionating column?

Short chain molecules, low viscosity, high flammability

Short chain molecules, low boiling point, low flammability

Long chain molecules, high flammability, high boiling point

Long chain molecules, high viscosity, high boiling point

The molecules with the greatest molar mass and longest chain are collected at the bottom. They have the highest boiling point and are hard to ignite

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14. 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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15. Which substances contain the same number of atoms?

A

B

C

D

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16. Water is formed when oxygen combines with hydrogen. What mass of oxygen combines with 6 g of hydrogen?

12 g

48 g

96 g

144 g

2H2 + O2 --> 2H2O

for H2,

1 mole --> 2g

6 g of hydrogen = 3 mole

H2 : O2

2 : 1

3 mole : 1.5 mole

1.5 mole of O2 = 32 x 1.5 = 48g

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17. 50.0 cm3 of 0.10 mol/dm3 silver nitrate, AgNO3, is added to 150.0 cm3 of 0.05 mol/dm3 of sodium iodide, NaI, in a beaker.

After the reaction, solid silver iodide is present in the beaker. What else is present in the mixture?

Ag+, Na+, NO3- only

Na+, I-, NO3- only

Na+, I- only

Na+, NO3- only

AgNO3 + NaI --> NaNO3 + AgI

50.0 cm3 of 0.10 mol/dm3 silver nitrate, AgNO3 = 0.005 mole

150.0 cm3 of 0.05 mol/dm3 of sodium iodide, NaI, = 0.0075 mole

Reactant ions left = Na+ and I -

product ions = Na+ and NO3^-

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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. 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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20. 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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