Class 8, NCERT (CBSE) Science Guide
MATERIALS : METALS AND NON-METALS
Answers of Sample (Model) Questions following latest CCE (CBSE) syllabus
Very Short Answer Questions (VSQ)
Answer Q.1: Gold and Silver.
Answer Q.2: Mercury.
Answer Q.3: K is the most reactive and Au is the least reactive metal.
Answer Q.4: Aluminium.
Answer Q.5: Silver.
Answer Q.6: Graphite.
Answer Q.7: Acidic nature.
Answer Q.8: Non-metals do not react with water.
Answer Q.9: A reaction in which a more reactive metal displaces the less reactive metal from its compound in aqueous solution is called displacement reaction. For example, when iron nails are dipped in copper sulphate solution, the iron being more reactive displaces copper from its solution and form ferrous sulphate solution of light green colour.
Fe + CuSO4 --> FeSO4 + Cu
Answer Q.10: Silver is less reactive than hydrogen therefore, it can not displace hydrogen from dilute hydrochloric acid.
Short Answer Questions (SQ)
Answer Q.11: Materials which make a ringing (metallic) sound when hit hard by some other material are called sonorous materials. All metals except the soft ones are sonorous while non-metals are not sonorous.
Malleability: The property of metals by which they can be beaten into thin sheets. This is one of the characteristic properties of metals.
Ductility: It is the property of metals by which they can be drawn into wires is called ductility.
Metals: Metals are those materials which are generally hard (except Na and K), lustrous, mostly exists in solid state (except mercury), malleable, ductile, sonorous and also good conductors of heat and electricity.
Non-Metals: Non-metals are those materials which are found in all the three states (solid, liquid and gas), non-lustrous, non-sonorous, neither malleable nor ductile and also bad conductors of heat and electricity. The oxides of non-metals are acidic in nature.
Metalloids: Metalloids are those materials which possess the qualities of both metals and non-metals.
Answer Q.13: In the presence of moisture iron reacts with oxygen to form Ferric Oxide (Fe2O3) which is brownish in colour. This is called ‘Rust’.
Answer Q.14: Mixture of two or more than two metals in order to get desired properties is called an alloy. For example, stainless steel is an alloy of iron, chromium and nickel. Stainless steel is very hard and also does not rust. So, it is used to make utensils, surgical instruments and many other products. Other alloys are like Brass, Bronze, Gun Metal etc.
Answer Q.15: Different metals react differently with water while hydrogen being a common end product. For example,
(a) Sodium metal reacts vigorously with water to form sodium hydroxide and hydrogen gas.
(b) Magnesium only reacts with hot boiling water to from magnesium oxide and hydrogen.
(c) Red hot iron reacts with steam to form iron oxide and hydrogen.
(d) Copper, nickel, and silver do not react with water.
Long Answer Questions
Answer Q.16: Both aluminium and brass are ductile, malleable and also can be easily casted into different shapes. Aluminium being a metal and brass an alloy, both of them are good conductor of heat. Because of the reasons aluminium and brass are used to make utensils.
(i) Iron is used in construction of bridges and houses because iron being a hard metal it forms reinforced concrete when casted with cement.
(ii) Aluminium is used for making electrical wires because of its following properties:
a. good conductor of electricity
c. cheaper than copper
(iii) Sulphur is a non-metal because:
a. it is neither malleable nor ductile
b. it combines with oxygen to form acidic oxide
c. does not conduct heat or electricity.
Answer Q.18: Following are some uses of non-metals –
1. Oxygen is used by plants and animals for respiration. It also supports the process of combustion.
2. Compounds of nitrogen provide nutrients to soil and plants. Fertilizers made of non-metallic compounds are extensively used in agriculture.
3. Chlorine is used as disinfectant.
4. Sulphur is used in germicide and as an antiseptic for skin treatment. It is also used in crackers.
1. Metals react with oxygen to produce oxides which are alkaline in nature.
2. Metals react with water differently to produce oxides and hydroxides.
3. They react with acids to produce H2 gas.
4. More reactive metals displace the less reactive metals from their compounds in aqueous solution.
1. Metals react with oxygen to produce oxides which are acidic in nature.
2. Non-metals do not react with water.
3. Non-metals generally react with acids
4. Non-metals do not show any such reaction.
Class VIII CBSE Science Guide | Chapter 4, Materials : Metals and Non-Metals | Ncert Solutions [Read]
Class 8 Ncert Cbse Science | Materials : Metals and Non-Metals | Notes and MCQ [Read]