Structure and Properties of Materials

Which compound contains three different non-metallic elements?

• SiH₂Cl₂

• BaSeO₄

• LiBH₄

• C₄H₈

Answer explanation

Silicon (Si), hydrogen (H) and Cl (chlorine) are non-metals.

Take note of the staircase line in the Periodic Table.

Which statement describes a pure compound?

• A yellow solution

• A liquid which gives two fractions when distilled

• Blue crystals which melt over the range from 55^oC to 60^oC

• Colourless solid which melts at 58^oC

Answer explanation

A pure substance melts and boils at fixed temperature. It cannot be separated through physical means, e.g. filtration or distillation.

An impure substance or a mixture melts and boils over a range of temperature.

Which diagram shows the particles found in air?

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Answer explanation

Air consists of nitrogen gas (N₂), oxygen gas (O₂), carbon dioxide (CO₂) and other gases.

78% of the air is nitrogen gas and 21% of the air is oxygen gas.

Which statement about sodium chloride and water is incorrect?

• Seawater does not have fixed composition but sodium chloride has.

• The properties of seawater is different from its components but the properties of sodium chloride is same as its components.

• Seawater can be separated by physical means but not sodium chloride.

• When sodium chloride is formed, heat and light are formed but not for the formation of seawater.

Three substances have the following electrical properties:

P - does not conduct electricity in any states

Q - conducts in both molten and aqueous states

R - conducts in both molten and solid state

What are P, Q and R?

• P: Methane, CH₄

  Q: KCl

  R: Fe

• P: Fe

  Q: KCl

  R: Methane, CH₄

• P: Fe

  Q: Methane, CH₄

  R: KCl

• P: Methane, CH₄

  Q: Fe

  R: KCl

Answer explanation

Methane is a covalent compound, hence it cannot conduct electricity in any states.

KCl is an ionic compound, hence it can conduct electricity in molten and aqueous states.

Fe is a metal which can conduct electricity in molten and solid states.

Which substance has an ionic lattice structure?

• Melting point: -114^oC

  Poor conductor of electricity in molten state

• Melting point: 98^oC

  Good conductor of electricity in molten state

• Melting point: 1000^oC

  Good conductor of electricity in molten state

• Melting point: 1610^oC

  Poor conductor of electricity in molten state

Answer explanation

Ionic compound has a giant ionic lattice structure, which made up of ions.

The melting point of this substance is high.

Due to its ions which are free to move around, the substance can conduct electricity in molten (liquid) and aqueous states.

Which diagram shows the structure of an alloy?

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Which is not a characteristic of the compound formed between magnesium and chlorine?

• It is a solid in room temperature.

• It has a high melting and boiling point.

• It is soluble in water.

• It cannot conduct electricity in any states.

Answer explanation

Magnesium is a metal and chlorine is a non-metal. Hence these elements combine to form ionic compound.

Ionic compound

~ has high melting point

~ is soluble in water

~ can conduct electricity in molten and aqueous states.

Why sodium chloride can conduct electricity in its molten or aqueous state?

Answer explanation

There are ions which are free to move around and carry the electrical charges.

State two properties that iron, zinc and copper have in common.

Answer explanation

These elements are metals.

1. high melting and boiling points

2. Good conductor of electricity.

3. Good conductor of heat

4. Malleable

5. Ductile

6. High density