This question is about transition metals, oxides of cobalt, and differences in lattice structures of oxides.
(a) Cobalt forms several oxides including CoO\text{CoO}CoO, Co2O3\text{Co}_2\text{O}_3Co2O3, and Co3O4\text{Co}_3\text{O}_4Co3O4.
A student carries out an experiment to identify an unknown cobalt oxide by reducing it to cobalt metal. The student heats the unknown cobalt oxide in a horizontal tube in a stream of carbon monoxide gas, CO\text{CO}CO.
Student's method:
Write the balanced equation for the reduction of Co3O4\text{Co}_3\text{O}_4Co3O4 with CO\text{CO}CO to form cobalt and carbon dioxide.
The student wears safety glasses and a lab coat. State, with a reason, one other important safety precaution the student should take when carrying out this experiment involving carbon monoxide.
Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed from the cobalt oxide. Explain your reasoning.
After making suitable modifications, the student repeats the experiment to obtain the following accurate results:
Calculate the empirical formula of the cobalt oxide.
SiO2\text{SiO}_2SiO2 and CO2\text{CO}_2CO2 are oxides of Group 14 elements. Solid SiO2\text{SiO}_2SiO2 melts at 1713 ∘C1713\text{ }^\circ\text{C}1713 ∘C while solid CO2\text{CO}_2CO2 sublimes at −78.5 ∘C-78.5\text{ }^\circ\text{C}−78.5 ∘C.
Suggest the type of lattice structure in solid SiO2\text{SiO}_2SiO2 and in solid CO2\text{CO}_2CO2, and explain the difference in melting/sublimation points in terms of the types of force within each lattice structure.
199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.