CBSE Class 10 Chemistry Metals and Non-metals MCQs Set 21

Answer: (a) \( \ce{ZnSO4} \) solution and aluminium metal

Explanation:
1. Aluminium is more reactive than zinc, so it displaces zinc from \( \ce{ZnSO4} \).
2. Al is less reactive than Mg, silver is less reactive than Fe and copper is less reactive than Na, so the other pairs do not react.

Teacher's Note:
1. Check that the metal is above the metal in the solution.
2. The order is Mg > Al > Zn > Fe > Cu > Ag.

Answer: (b) 5, 6, 7 and 8

Explanation:
1. Non-metals generally have 4 or more valence electrons, most commonly 5, 6, 7 and 8.
2. Metals usually have 1, 2 or 3.

Teacher's Note:
1. Metals lose electrons, non-metals gain electrons.
2. Hydrogen and helium are exceptions.

Answer: (a) Hg

Explanation:
1. Cinnabar is mercuric sulphide, HgS.
2. It is the main ore of mercury.

Teacher's Note:
1. On roasting, HgS gives mercury directly.
2. Galena is the ore of lead and zinc blende of zinc.

Answer: (c) Gangue

Explanation:
1. Earthy impurities such as sand and clay in an ore are called gangue.
2. Flux is added to remove gangue as slag.

Teacher's Note:
1. Gangue plus flux gives slag.
2. Slag is the fusible waste formed.

Answer: (a) Galena

Explanation:
1. Froth flotation is used for sulphide ores such as galena (PbS).
2. Cassiterite and magnetite are oxides and malachite is a carbonate.

Teacher's Note:
1. Sulphide ores are wetted by oil, gangue by water.
2. Copper pyrites and zinc blende are also concentrated by froth flotation.

Answer: (c) Rock salt

Explanation:
1. Copper pyrites, copper glance and zinc blende are sulphide ores, which are concentrated by froth flotation.
2. Rock salt is a chloride, not a sulphide.

Teacher's Note:
1. Froth flotation needs sulphide ores.
2. Rock salt is a source of sodium chloride.

Answer: (a) levigation

Explanation:
1. Levigation (hydraulic washing or gravity separation) uses a stream of water to carry away lighter gangue and leave the heavy ore.
2. Leaching is dissolving the ore in a chemical.

Teacher's Note:
1. This method is used for heavy oxide ores such as haematite.
2. The ore and gangue must differ in density.

Answer: (c) NaOH

Explanation:
1. In the Bayer process bauxite is treated with hot concentrated NaOH solution.
2. The alumina dissolves as sodium aluminate, leaving the iron oxide impurities.

Teacher's Note:
1. Bayer process purifies bauxite for aluminium.
2. Hall-Heroult electrolysis follows.

Answer: (d) Metallurgy

Explanation:
1. Metallurgy is the whole process of extracting a metal from its ore.
2. It includes concentration, reduction and refining.

Teacher's Note:
1. Concentration is only the first step.
2. Refining is the last.

Answer: (c) both (a) and (b)

Explanation:
1. In roasting a sulphide ore is heated strongly in excess air.
2. It is converted to oxide and volatile impurities like sulphur dioxide are driven off.

Teacher's Note:
1. Roasting is for sulphide ores, calcination for carbonate ores.
2. Both are done below the melting point of the ore.

Answer: (b) Roasting

Explanation:
1. A sulphide ore is heated in excess air giving oxides and \( \ce{SO2} \), which is roasting.

Teacher's Note:
1. Roasting gives oxide and sulphur dioxide.
2. This is a step in the extraction of copper from copper pyrites.

Answer: (d) None of these

Explanation:
1. Carbon, aluminium and zinc can all be used as reducing agents for suitable metal oxides.
2. So every choice can be used.

Teacher's Note:
1. A reducing agent must be more reactive than the metal produced.
2. Carbon is used for moderately reactive metals, aluminium for the less easily reduced.

Answer: (b) to reduce it

Explanation:
1. Smelting is heating the roasted or calcined ore with a reducing agent such as carbon to get the metal.

Teacher's Note:
1. Smelting is a reduction process.
2. It is carried out in a blast furnace for iron.

Answer: (b) Al

Explanation:
1. In the thermite process aluminium powder reduces metal oxides like \( \ce{Fe2O3} \).
2. \( \ce{Fe2O3 + 2Al -> Al2O3 + 2Fe} \) gives molten iron.

Teacher's Note:
1. Aluminium has a high affinity for oxygen.
2. The reaction is used to weld railway tracks.

Answer: (c) \( \ce{Al2O3} \)

Explanation:
1. Carbon can reduce the oxides of moderately reactive metals such as Zn, Fe and Pb.
2. Aluminium is above carbon in reactivity and its oxide is not reduced by carbon.
3. It is extracted by electrolysis of molten alumina.

Teacher's Note:
1. Highly reactive metals are extracted by electrolysis.
2. Aluminium has a very strong bond with oxygen.

Answer: (a) highly reactive

Explanation:
1. The oxides of highly reactive metals (Na, Mg, Ca, Al) cannot be reduced by carbon.
2. They are obtained by electrolysis of their molten chlorides or oxides.

Teacher's Note:
1. Reactive metals are extracted by electrolysis.
2. Unreactive metals occur free or from simple heating.

Answer: (b) Solid NaCl

Explanation:
1. Ions are free to move in fused NaCl and in brine, and electrons move in copper.
2. In solid NaCl the ions are held in fixed positions, so it does not conduct.

Teacher's Note:
1. Ionic compounds conduct only when molten or dissolved.
2. Metals conduct in the solid state.

Answer: (b) highly electropositive metals

Explanation:
1. Highly electropositive metals such as Na, K, Ca and Al are extracted by electrolytic reduction of their molten salts.

Teacher's Note:
1. Electropositive means readily forming cations.
2. Noble metals occur in the free state.

Answer: (d) Al

Explanation:
1. Aluminium is obtained by electrolysis of molten alumina in cryolite.
2. Fe is obtained by carbon reduction and Cu and Ag by other methods.

Teacher's Note:
1. Cryolite lowers the melting point of alumina.
2. Graphite electrodes are used.

Answer: (c) fused sodium chloride

Explanation:
1. Electrolysis of molten (fused) sodium chloride gives sodium at the cathode and chlorine at the anode.
2. Aqueous solutions give hydrogen at the cathode instead.

Teacher's Note:
1. Water is reduced in preference to sodium ions in solution.
2. So molten salt is needed.

Answer: (c) iron oxide

Explanation:
1. Rust is hydrated iron(III) oxide, \( \ce{Fe2O3.xH2O} \).

Teacher's Note:
1. Rusting needs both oxygen and water.
2. Aluminium and copper form different coatings.

Answer: (a) nickel and chromium

Explanation:
1. Stainless steel is an alloy of iron, carbon, nickel and chromium.
2. These resist rusting.

Teacher's Note:
1. An alloy is a homogeneous mixture of a metal with other elements.
2. Brass is copper plus zinc.

Answer: (b) Tungsten

Explanation:
1. Stainless steel contains iron, chromium, nickel and carbon.
2. Tungsten is not a regular component.

Teacher's Note:
1. Chromium gives the corrosion resistance.
2. Tungsten is used in bulb filaments.

Answer: (c) zinc is more reactive than tin

Explanation:
1. Zinc is more reactive than tin and would react with the acids in food.
2. Tin is less reactive and keeps the food safe.

Teacher's Note:
1. A food container must not react with its contents.
2. Tin is less reactive than iron and zinc.