Long ANSWER-Class 10 – Science -Chemistry -Chapter 3 – Metals and Non-metals

Q1. What is Thermit Reaction? Explain its use and give equation.

Ans:

A thermite reaction is basically iron oxide (rust) reacting with aluminium to produce molten iron. The products are aluminium oxide, elemental iron, and a large amount of heat. The reactants are commonly or thermite mixture is aluminium powder and iron oxide (rust) powder. When the mixture is heated, it starts reacting as the aluminium is more reactive than the iron and aluminium forms stronger and stable bonds with oxygen than iron.

Uses-

1.The reaction is used for thermite welding, often used to join rail tracks. 2.Thermites have extremely high temperature and also been used in metal refining, demolition of ammunitions, and2 in incendiary weapons.

3.Some thermite-like mixtures are used in fireworks.

4.A thermite reaction is used to purify the ores of some metals called as thermite process.

Fe₂ O₃ + 2 Al –> Al₂ O₃ + 2Fe

Q2 How does the method used for extracting a metal from its ore depend on the metal’s position in the reactivity series? Explain with examples.

Ans

Reactivity series depicts the reactivities of metals in decreasing order. It is very helpful in the extraction of metals. The extraction of metals depends on their reactivities.

For extraction purpose, metals in the reactivity series are ordered under three sections:

1. Highly reactive metals

2. Moderately reactive metals

3. Low reactive metals

Depending on the reactivities, different methods are applied for extracting metals from their ores.

Sodium, potassium, calcium, magnesium and aluminium are highly reactive metals and placed at the top of the reactivity series. These metals are extracted by electrolytic reduction of their molten chlorides or oxides because these metals are not reduced by other reducing agents like coke, carbon monoxide etc.

Moderately reactive metals like zinc, iron, lead and copper are placed at the middle of the reactivity series. They are reduced by carbon because carbon is more reactive than these metals and can reduce their metal oxides to metal easily. However, manganese is more reactive than zinc (above zinc in reactivity series); therefore, it cannot be reduced by carbon. It is reduced by a more reactive reducing agent aluminium. Aluminium reduces manganese dioxide to manganese on heating.

Low reactive metals like copper and mercury are placed at the bottom of the reactivity series and are extracted by heating their ores alone. We should note that ores of copper can be extracted by both: reduction with carbon (copper (I) oxide) and heating alone (copper (I) sulphide).

Q3. (a) What is meant by corrosion? Name any two methods used for the prevention of corrosion.

(b) Suppose you have to extract metal M from its enriched sulphide ore. If M is in the middle of the reactivity series, write various steps used in extracting this metal.

Ans. (a) Corrosion is a process in which metal reacts with substances present in the environment to form surface compounds.

Prevention:

(i) Galvanisation is a process to prevent corrosion of iron.

(ii)Electroplating is also used to prevent corrosion.

(b)(i) Concentration of ores: Sulphide ore will be concentrated by froth- floatation process. Sulphide ore will be collected in froth whereas gangue will be left behind.

(ii) Roasslng: Sulphide ore is heated strongly in the presence of O2 to form metal oxide and sulphur dioxide.

2MS + 3O2 ————- ► 2MO + 2SO2

(iii) Reduction: MO reacts with carbon (acts as reducing agent) to form metal and CO.

MO + C —-> M + CO

(iv)Electrolytic refining: Impure metal ‘M’ is purified by electrolytic refining. Impure metal is taken as anode, pure metal is taken as cathode, soluble salt of metal is taken as electrolyte. Impure metal forms metal ions which gain electrons and form pure metal at cathode.