Question

(a) Which metal is extracted from calamine ore?
(b) Name one ore of mercury. Which mercury compound is present in this ore? Write its chemical formula.
(c) How is copper extracted from its sulphide ore (copper glance), Cu₂S? Explain with equations of the reactions involved.
(d) What is an alloy? Give two examples of alloys.
(e) How are the properties of an alloy different from those of the constitutent elements?

Answer 1

(a) Zinc metal is extracted from calamine ore. Calamine ore is a carbonate ore. The compound present in it is zinc carbonate. Its formula is ${\mathrm{ZnCO}}_3$.

(b) The ore of mercury is cinnabar. Cinnabar is a sulphide ore. The compound present in it is mercury (II) sulphide. Its chemical formula is HgS.

(c) The sulphide ore of copper is copper glance. The compound present in the ore is copper (I) sulphide. Its formula is ${\mathrm{Cu}}_2\mathrm{S}$. Copper is a less reactive metal; therefore, it is placed at the bottom in the reactivity series. Copper is extracted by heating its sulphide ore alone.

Two steps involved in the extraction of copper metal from concentrated copper glance ore are:

1. Roasting: Copper glance, being a sulphide ore, is heated in the presence of air. Copper (I) sulphide is converted to copper (I) oxide.
${\mathrm{2Cu}}_2\mathrm{S}\left(s\right)+{\mathrm{3O}}_2\left(g\right)\underset{\mathrm{Surplus}\mathrm{air}}{\overset{\mathrm{Roasting}}{\to }}{\mathrm{2Cu}}_2\mathrm{O}\left(s\right)+{\mathrm{2SO}}_2\left(g\right)$

2. Copper (I) oxide, so formed, reacts with non-oxidised copper (I) sulphide ore in the absence of air to form copper metal. When the mixture of ${\mathrm{Cu}}_2\mathrm{O}$ and ${\mathrm{Cu}}_2\mathrm{S}$ is heated, they react together to give copper metal and sulphur dioxide gas.
${\mathrm{2Cu}}_2\mathrm{O}\left(s\right)+{\mathrm{Cu}}_2\mathrm{S}\left(s\right)\stackrel{\mathrm{Heat}}{\to }\mathrm{6Cu}\left(s\right)+{\mathrm{SO}}_2\left(g\right)$

(d) A uniform combination of two or more metals or a metal with a non-metal is called an alloy. Alloys are produced by mixing metals in their molten state in desired quantities and allowing the solution to cool at the room temperature. Similarly, an alloy of a metal and non-metal is prepared by dissolving the non-metal in the molten metal and allowing the solution to cool at the room temperature.
Examples: Steel is an alloy of iron. The composition of steel is iron with 0.1 to 1.5 % carbon.
Brass is an alloy of copper and zinc. Its composition is 80 percent copper and 20 percent zinc.

(e) The properties of alloys are different from those of the constituent elements :

1. Alloys have higher strength than their constituting metals. Example: Steel is an alloy of iron with carbon and it has higher strength than iron.

2. Alloys are harder than their constituting metals. Example: Magnalium is an alloy of aluminium and magnesium and it is harder than aluminium.

3. Alloys have high resistance to corrosion than their constituting metals.​ Example: Stainless steel is an alloy of iron, nickel and chromium, and it does not corrode at all, whereas iron rusts easily.

4. Alloys have lesser melting points than their constituting metals.​ ​Example: Solder an alloy of tin and lead and it has a very low melting point, which is less than its constituting metals.

5. Alloys have low electrical conduction than their constituting metals.​ ​Example: Copper is an excellent conductor of electricity but brass (alloy of copper and zinc) and bronze (alloy of copper and tin) are poor conductors of electricity.