Cryolite is added to alumina in the Hall-Heroult cell to
ACoat the cathode with a thin layer of carbon
BRaise the melting point and slow the reaction
CProduce coloured aluminium for jewellery use
DLower the melting point and improve conductivity
Answer & Solution
Correct answer: D. Lower the melting point and improve conductivity
1. Pure alumina melts above 2000 deg C.
2. Adding cryolite (Na3AlF6) lowers the melt to about 950 deg C.
3. It also increases the electrical conductivity.
4. So option A is correct.
_Source: Selina Concise Chemistry Class 10, Ch 7 Metallurgy (Mistral OCR'd PDF), section on cryolite role_
Related questions
Germanium and silicon used as semiconductors are purified by zone refining becauseNickel is refined by heating the impure metal in a stream of CO to form a volatile carbonyFrom an Ellingham diagram at 1500 K, $\Delta G^\circ$ for $2Fe+O_2\rightarrow 2FeO$ is $-3From an Ellingham diagram, aluminium can reduce which of the following oxides?In an Ellingham diagram the line for the formation of carbon monoxide ($2C + O_2
ightarroAn Ellingham diagram is a plot ofIn the cyanide process, gold is recovered from the leached solution $[Au(CN)_2]^-$ by addiIn the electrolytic refining of copper, the anode and cathode are respectively