Online Test: General Principles and Processes of Isolation of Elements | Class 12 Chemistry

Question 1 of 20

A mineral from which a metal can be extracted profitably is called a/an:

ore

gangue

flux

slag

Explanation: An ore is a mineral that yields the metal economically; gangue is the impurity.

Question 2 of 20

Galena is an ore of:

zinc

lead

copper

mercury

Explanation: Galena is lead sulphide, $PbS$.

Question 3 of 20

Froth flotation is used mainly for:

oxide ores

carbonate ores

sulphide ores

halide ores

Explanation: Sulphide particles are wetted by oil and float with the froth.

Question 4 of 20

The depressant used to separate $ZnS$ from $PbS$ in froth flotation is:

pine oil

NaOH

NaCl

NaCN

Explanation: NaCN complexes zinc as $[Zn(CN)_4]^{2-}$, keeping $ZnS$ down while $PbS$ floats.

Question 5 of 20

Leaching of bauxite uses:

hot conc. NaOH

NaCN

dilute HCl

water

Explanation: The Bayer process digests bauxite in hot concentrated NaOH to give soluble $NaAlO_2$.

Question 6 of 20

Roasting of a sulphide ore evolves:

$CO_2$

$SO_2$

$H_2$

$NO$

Explanation: e.g. $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$.

Question 7 of 20

Calcination is carried out in:

excess air

pure oxygen

limited/no air

hydrogen

Explanation: Calcination heats carbonate/hydrated ores in limited air to remove $CO_2$ and water.

Question 8 of 20

For a feasible reduction, the sign of $\Delta G$ must be:

positive

zero

undefined

negative

Explanation: Only $\Delta G < 0$ makes the reduction spontaneous.

Question 9 of 20

The relation between standard Gibbs energy and equilibrium constant is:

$\Delta G^0 = -RT\ln K$

$\Delta G^0 = RT\ln K$

$\Delta G^0 = -RT/K$

$\Delta G^0 = K/RT$

Explanation: $\Delta G^0 = -RT\ln K$; a more negative $\Delta G^0$ gives a larger $K$.

Question 10 of 20

On the Ellingham diagram the carbon-to-CO line:

slopes up

slopes down

is flat

is vertical

Explanation: CO formation increases gas moles ($\Delta S>0$), so $\Delta G^0$ falls as $T$ rises.

Question 11 of 20

The thermite reaction reduces ferric oxide using:

carbon

CO

aluminium

zinc

Explanation: $2Al + Fe_2O_3 \rightarrow 2Fe + Al_2O_3$ gives molten iron for welding.

Question 12 of 20

Self-reduction is used to extract:

aluminium

chromium

sodium

copper

Explanation: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$ needs no external reducer.

Question 13 of 20

Mercury is refined by:

distillation

liquation

zone refining

electrolysis

Explanation: Mercury boils low, so distillation gives the pure metal.

Question 14 of 20

Anode mud during copper refining is rich in:

iron

silver and gold

zinc

sulphur

Explanation: Noble Ag and Au do not dissolve and settle below the anode.

Question 15 of 20

Zone refining is based on the fact that impurities are:

less soluble in the melt

magnetic

more soluble in the melt

volatile

Explanation: Impurities concentrate in the molten zone, which is swept to one end.

Question 16 of 20

The Mond process refines nickel through the volatile species:

$NiCl_2$

$NiO$

$NiI_4$

$Ni(CO)_4$

Explanation: $Ni + 4CO \rightarrow Ni(CO)_4 \rightarrow Ni + 4CO$.

Question 17 of 20

In the Hall-Heroult process, alumina is dissolved in molten:

cryolite

fluorspar only

limestone

silica

Explanation: Cryolite ($Na_3AlF_6$) lowers the melting point and increases conductivity.

Question 18 of 20

In the blast furnace the slag formed is:

$CaO$

$CaSiO_3$

$SiO_2$

$FeSiO_3$

Explanation: $CaO + SiO_2 \rightarrow CaSiO_3$, a fusible slag floating on the molten iron.

Question 19 of 20

Magnetite is:

$Fe_2O_3$

$FeCO_3$

$Fe_3O_4$

$FeS_2$

Explanation: Magnetite is $Fe_3O_4$, a magnetic oxide ore of iron.

Question 20 of 20

Aluminium cannot be extracted by carbon reduction because:

Al is volatile

alumina is a sulphide

carbon is too cheap

the Al oxide line lies below the carbon line

Explanation: The $Al/Al_2O_3$ line is below C/CO to very high T, so $\Delta G$ cannot be made negative.

Online Test — General Principles and Processes of Isolation of Elements