Metals above carbon in the reactivity series
3 marks · EasyThe diagram shows the extraction of aluminium from aluminium oxide.
Aluminium oxide is dissolved in molten cryolite and electrolysed.
State the formula of aluminium oxide.
Give the reason why cryolite is used in this process.
Write the half-equation for the reaction at the cathode.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) \( \ce{Al2O3} \ )
(b) It lowers the melting point of aluminium oxide.
(c) \( \ce{Al^{3+} + 3e^- -> Al} \ )
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct formula of aluminium oxide: Al2O3
B2 (b) · 1 mark · Cryolite lowers the melting point of aluminium oxide (accept: reduces the amount of energy needed).
B3 (c) · 1 mark · Correct half-equation at the cathode: Al3+ + 3e- -> Al (accept with or without state symbols, arrow either way).
Worked solution
a) The formula of aluminium oxide is .
b) Cryolite is used to lower the melting point of aluminium oxide so less energy is needed for electrolysis.