NCERT Solutions for Class 8 Science Chapter 4 - Materials : Metals And Non Metals

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Answer:

(a) Zinc

Answer:

(c) Generally, metals are ductile

However, mercury metal− a liquid at room temperature − cannot be drawn into wires and is not ductile.

Answer:

(a) Phosphorus is a very __reactive__ non-metal.

(b) Metals are __good__ conductors of heat and __electricity__.

(c) Iron is __more__ reactive than copper.

(d) Metals react with acids to produce __hydrogen__ gas.

Answer:

(i) Generally, non-metals react with acids. (F)

(ii) Sodium is a very reactive metal. (T)

(iii) Copper displaces zinc from zinc sulphate solution. (F)

(iv) Coal can be drawn into wires. (F)

Answer:

Answer:

(a) Aluminium foils are used to wrap food items because aluminium metal is malleable. Therefore, it can be beaten into thin foils.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods for heating liquids are made of metallic substances.

(c) A metal can displace a less reactive metal from its salt in an aqueous solution. But zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.

Cu_(s) + ZnSO_{4 (aq)}→ No reaction

(d) Sodium and potassium are stored in kerosene because they are highly reactive elements. They can easily catch fire even when in contact with air.

Answer:

Lemon pickle cannot be stored in aluminium utensils because lemon pickle contains acids, which can react with aluminium (metal) liberating hydrogen gas. This can lead to the spoiling of the pickle.

Answer:

Answer:

(a) When dilute sulphuric acid is poured on a copper plate, there will be evolution of hydrogen gas along with the formation of blue color crystals of coppersulphate.

${\mathrm{CuSO}}_4 + {\mathrm{H}}_2{\mathrm{SO}}_{4 } \to {\mathrm{CuSO}}_4 + {\mathrm{H}}_2$

(b) Iron being more reactive displaces copper from copper sulphate solution. In this reaction, the blue colour of copper sulphate fades and there is deposition of copper on the iron nail.

Answer:

(a) Add a few drops of water in the test tube containing gas. Now, cover the test tube and shake it well. After shaking, test the solution with blue litmus and red litmus. It will turn blue litmus red. Thus, the gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas.

Carbon dioxide reacts with water to form carbonic acid, which turns blue litmus paper red.

Answer:

To polish a gold ornament, it is dipped in a liquid called aqua regia (a mixture of hydrochloric acid and nitric acid). On getting the environment of aqua regia, the outer layer of gold dissolves and the inner shiny layer appears. The dissolving of the layer causes a reduction in the weight of the jewellery.