O Levels Combined Chemistry G3

O Levels G3 Combined Chemistry Paper 1 mock

Name

1 / 20

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

2 / 20

Calcium nitrate crystals contain water of crystallisation. Its formula may be written as Ca(NO3)2●nH2O.

When a 7.00 g sample of hydrated calcium nitrate is heated to remove all water, 4.90 g of anhydrous calcium nitrate remains after heating.

What is the value of n?

1

2

3

4

7 g - 4.9 g = 2.1g of water

1 mole water --> 18g

2.1 g --> 0.11667 mole

1 mole Calcium nitrate --> 164g

4.9g --> 0.029878 mole

ratio

0.029878 : 0.11667

1 : 4

3 / 20

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

caesium

lithium

potassium

rubidium

reactivity increases as it goes down the group.

4 / 20

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

5 / 20

Which compound has the lowest percentage by mass of nitrogen?

(NH2)2CO

(NH4)2SO4

(NH4)3PO4

NH4NO3

% of N in (NH2)2CO = 46.65 %

% of N in (NH4)2SO4 = 21.2%

% of N in (NH4)3PO4 = 28.18%

% of N in NH4NO3 = 35%

6 / 20

CH4, H2O and HCl are covalent compounds.

Which atoms in these compounds do not use all their outer shell electrons in bonding?

C and H

C and O

O and Cl

Cl and C

O has 6 valence electrons and only uses 2 for bonding

Cl has 7 valence electrons and only uses 1 for bonding

7 / 20

Which element does not form a stable ion with the same electronic configuration as neon?

Magnesium

Fluorine

Sodium

Sulfur

Sulfur is 2,8,6 so when it form an ion, it will be 2,8,8 which is the electron configuration of Argon

8 / 20

Which property of elements increases from left to right of Period 3 of the Periodic Table?

number of outer shells

metallic character

tendency to get reduced

melting points

As you move from left to right across a period, the number of protons in the nucleus increases, which leads to a stronger attraction for electrons. This increased attraction makes it more difficult for an atom to lose electrons,

9 / 20

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

10 / 20

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

11 / 20

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

12 / 20

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.

13 / 20

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

14 / 20

When excess aluminium oxide, Al2O3 was added to a portion of dilute sodium hydroxide. Which of the following correctly describes the pH change and the explanation?

A

B

C

D

Aluminium oxide is amphoteric and neutralises the sodium hydroxide. Thus the pH decrease

15 / 20

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.

16 / 20

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 %

17 / 20

Which of the following is the process by which a polyester is broken down into its monomers?

condensation

esterification

hydrolysis

polymerisation

Hydrolysis of polymers is a chemical process where water molecules break down polymer chains

18 / 20

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

19 / 20

A solution of a lithium halide and a halogen are mixed. A reaction occurs and the mixture darkens in colour.

What are the reactants?

bromine and lithium chloride

iodine and lithium fluoride

chlorine and lithium iodide

chlorine and lithium fluoride

Since the solution darken, there must be displacement.

20 / 20

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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