Metals towards the top of the activity series cannot be obtained from their compounds by reducing with carbon. Why?

Metals such as sodium, magnesium, calcium, aluminium are placed towards the top of the activity series, they are highly reactive metals. These metals cannot be obtained from their compounds by heating with carbon. This is because they have more affinity for oxygen than carbon. So the oxides of such metals are very stable in nature. Hence, the oxides of very reactive metals cannot be reduced with carbon. These metals can be obtained by electrolytic reduction. In this process, metals are extracted from their oxides or chlorides in a molten state.

List one metal found in the free state in the earth’s crust and mention where it is located in the activity series.

The metal gold is found in the free state in the earth’s crust. Gold is chemically inactive, highly resistant to oxidation and corrosion, so it is found in the free state in the earth’s crust. Platinum is also found in the free state in the earth’s crust. These metals are located at the bottom in the activity series. They are called noble metals.

Explain any two properties of ionic compounds.

Ionic compounds are neutral compounds made up of positively charged ions called cations and negatively charged ions called anions. Two properties of ionic compounds are as follows: 1. Ionic compounds have high melting and boiling points because the force of attraction between ions of ionic compounds is very strong. 2. Ionic compounds dissociate into ions when dissolved in water. So, the solutions of ionic compounds and molten ionic compounds conduct electricity, but solid materials do not.

Explain the steps involved in the extraction of metals from their ores.

The common steps involved in the extraction of metals from their ores are: (1) Crushing and pulverisation (2) Concentration or dressing of the ore (3) Conversion of ore into metal oxide(calcination or roasting) (4) Reduction of metal oxides to free metal (5) Purification and refining of metal. (1) Crushing and pulverisation: Ores are broken into small pieces with the help of crushers. These pieces are then reduced to a fine powder with the help of a ball mill or a stamp mill. (2) Concentration or dressing of the ore: The process of removal of unwanted impurities (gangue) from the ore is called ore concentration. It can be done by hydraulic washing, magnetic separation, froth floatation, leaching, etc. (3) Conversion of ore into metal oxide: It can be done by two processes calcination (for carbonate ores) and roasting (sulphide ores). The calcination is carried out in a limited supply of air or absence of air. Roasting involves the heating of ore lower than its melting point in the presence of air or oxygen. (4) Reduction of metal oxide into free metal: This process depends upon the nature and chemical reactivity of the metal. For low reactive metals, the self-reduction process is used. For middle reactive metals, carbon reduction, reduction with CO or reduction with aluminium is involved. For high reactive metals, an electrolytic reduction is used. (5) Purification and refining of metal: Distillation refining is used for refining volatile metals e.g. Zn , Hg . Liquation is used for refining low melting point metals e.g. lead, tin. Electrolytic refining is used for metals like Cu , Al , etc.

What are amphoteric oxides?

The metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. These oxides have the properties of both acidic and basic oxides, so they can neutralise both acids and bases. Examples of amphoteric oxides are zinc oxide( ZnO ) and aluminium oxide( Al 2 O 3 ).