Structured Questions

2012 May June Paper 21 Q1

The elements carbon and silicon are both in Group IV of the Periodic Table. Carbon is the second most abundant element by mass in the human body and silicon is the second most common element in the Earth’s crust.
Carbon and silicon each form an oxide of general formula \(XO _{2}\). At room temperature, \(CO _{2}\) is a gas while \(SiO _{2}\) is a solid with a high melting point.


(a) Briefly explain, in terms of the chemical bonds and intermolecular forces present in each compound, why \(CO _{2}\) is a gas and \(SiO _{2}\) is a solid at room temperature. [3]

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(b) Draw a simple diagram to show the structure of \(SiO _{2}\). Your diagram should contain at least two silicon atoms and show clearly how many bonds each atom forms.

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\(CO _{2}\) does not behave as an ideal gas.
(c) (i) State the basic assumptions of the kinetic theory as applied to an ideal gas. [4]

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(ii) Suggest one reason why \(CO _{2}\) does not behave as an ideal gas. [1]

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Carbon exists in a number of forms, one of which is a conductor of electricity and one of which is a non-conductor of electricity. Silicon is the main component of most semi-conductors.
(d) Graphite is the form of carbon that is a conductor of electricity. Give a simple explanation for this property. [1]

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When carbon and silicon(IV) oxide are heated together at about \(2000^{\circ} C\), silicon carbide, \(SiC\), is formed. Silicon carbide is a hard material which is widely used as anrasive and in ceramics.

(e) (i) Construct an equation for the reaction of carbon and silicon(IV) oxide.

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(ii) SiC has a similar structure to one of the common forms of carbon. Which form is this? Give a reason for your answer. [2]
form
reason

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