4.2. Bonding and structure
A subsection of Chemistry, 9701, through 4. States of matter
Listing 10 of 122 questions
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 XO2. At room temperature, CO2 is a gas while SiO2 is a solid with a high melting point. Briefly explain, in terms of the chemical bonds and intermolecular forces present in each compound, why CO2 is a gas and SiO2 is a solid at room temperature. Draw a simple diagram to show the structure of SiO2. Your diagram should contain at least two silicon atoms and show clearly how many bonds each atom forms. CO2 does not behave as an ideal gas. State the basic assumptions of the kinetic theory as applied to an ideal gas. Suggest one reason why CO2 does not behave as an ideal gas. 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. Graphite is the form of carbon that is a conductor of electricity. Give a simple explanation for this property. When carbon and silicon(oxide are heated together at about 2000 °C, silicon carbide, SiC, is formed. Silicon carbide is a hard material which is widely used as an abrasive and in ceramics. Construct an equation for the reaction of carbon and silicon(oxide. SiC has a similar structure to one of the common forms of carbon. Which form is this? Give a reason for your answer. form reason
9701_w09_qp_22
THEORY
2009
Paper 2, Variant 2
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Calcium chloride, CaCl2, is an important industrial chemical used in refrigeration plants, for de-icing roads and for giving greater strength to concrete. Show by means of an equation what is meant by the lattice energy of calcium chloride. Suggest, with an explanation, how the lattice energies of the following salts might compare in magnitude with that of calcium chloride. calcium fluoride, CaF2 calcium sulfide, CaS Use the following data, together with additional data from the Data Booklet, to calculate the lattice energy of CaCl2. standard enthalpy change of formation of CaCl2 –796 kJ mol–1 standard enthalpy change of atomisation of Ca+178 kJ mol–1 electron affinity per mole of chlorine atoms –349 kJ mol–1 enthalpy Ca+ Cl 2lattice energy = kJ mol–1 When a solution of CaCl2 is added to a solution of the dicarboxylic acid, malonic acid, the salt calcium malonate is precipitated as a white solid. The solid has the following composition by mass: Ca, 28.2 %; C, 25.2 %; H, 1.4 %; O, 45.2 %. Calculate the empirical formula of calcium malonate from these data. Suggest the structural formula of malonic acid.
9701_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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