Friday, May 13, 2016

CBSE Class 8 - Science - METALS and NON Metals : Question and Answers

METALS and NON Metals : 
Question and Answers

Prachi Class 8 Science Textbook Solutions

CBSE Class 8 - Science - METALS and NON Metals : Question and Answers
Activity Series

Q1: Identify the type of elements which are neither malleable nor ductile.

Answer: Non-metals (eg Carbon, Phosphorous, Sulphur, Nitrogen) are neither malleable nor ductile.

Q2: Name a property which is common to the metals occurring near the bottom of the reactivity series.

Answer: These (Silver, Gold and Platinum) are least reactive metals and are found in free state in the earth's crust.

Q3: Name a metal that is kept under kerosene.

Answer: Sodium.

Q4: What type of reaction is the reaction between copper sulphate solution and zinc plate?

Answer: It is a displacement reaction.
        Zn + Copper Sulphate ---------> Zinc Sulphate + Copper

(Explanation: Zinc is more reactive than copper, Therefore Zn displaces Cu.)

Q5: An oxide of sulphur turns blue litmus red. Is it acidic or basic?

Answer: Acidic

Q6: Classify the following into metals and non-metals: Iodine, Lead, Carbon, Sulphur, Aluminium, Silicon

Answer: Metals: Lead, Aluminium
               Non-metals: Iodine, Carbon, Sulphur, Silicon

Q7: What is meant by reactivity series of metals?

Answer: The reactivity series of metals is an arrangement of metals in vertical column in order of decreasing reactivity.

Q8: Which of the following are (a) acidic (b) basic oxides?
Phosphorous pentoxide, Sulphur trioxide, Sodium oxide, Magnesium Oxide

Answer: Acidic Oxides: Phosphorous pentoxide, Sulphur trioxide
Basic Oxides:  Sodium oxide, Magnesium Oxide

(Explanation: Metal oxides are basic in nature. Non-metal oxides are acidic.)

Q9: Mention one main use of each of the following:
Copper, Aluminium, Phosphorous and Hydrogen.

Answer: Copper: Making electrical wires and utensils.
Aluminium:Electrical Wires, Utensils, Paints, Foil for packaging
Phosphorous: Match Sticks, Fertlizers, Rat Poison
Hydrogen: As a fuel, In oxygen-Hydrogen Flame for welding, Hydrogenation of Vanaspati Ghee

Q10: Write the word equations for the reaction: Reaction of magnesium with boiling water.


Magnesium + Water     --------------> Magnesium Hydroxide + Hydrogen

Magnesium reacts with boiling water and gives Magnesium hydroxide and hydrogen gas.

Q11: Mention some physical properties of metals.

Answer: 1. Most of the metals are solids.
2. Metals have lusture.
3. Metals are malleable and ductile.
4. In general metals are hard and have high tensile strength.
5. Metals have high melting and boiling points.
6. Metals are good conductor of heat and electricity.
7. Metals have high density.
8. Metals are sonorous.

Q12: More reactive metals occur in combined form, whereas less reactive metals occur as free metal in nature. Give reasons.

Answer: More reactive metals react readily with oxygen, carbon-dioxide and water present in air and form oxides, carbonates and hydroxides. That's why reactive metals occur in combined form. Least reactive metals do not react with O2, CO2 or water present in air, thus they are found in free state.

Q13: Describe the reaction:
Magnesium + Copper Sulphate Solution    --------->    Magensium Suphate + Copper
in terms of reactivity series of metals.

Answer: According to activity series of metals, Magnesium is more reactive than Copper. Mg displaces Cu and forms Magnesium Sulphate. It is a displacement reaction.

Q14: What is meant by malleability? Name the most malleable metal.

Answer: It is the ability of a metal which can be hammered into thin sheets. Gold and Silver are the most malleable metals.

Q15: Mention the main uses of the following:
     Phosphorous, Sulphur, Copper, Iron, Aluminium, Hydrogen

Answer: Phosphorus: Match Sticks, Fertilizers, Also used in pesticides and water treatment.
Sulphur: Gun Powder, Sulphuric Acid preparation, Vulcanization of rubber.
Copper: Electrical wires and cables, utensils, coins
Iron: Bridges, Engine Parts, Stainless Steel, Iron Bars used in constructions
Aluminium: Electric Wires, Utensils, Metallic paint, Aeroplane body
Hydrogen: As a fuel, Oxy flame used in welding, Hydrogenation of Vegetable ghee.

Q16: Tick the ODD-ONE out giving reason:

  (a) Hydrogen, Oxygen, Suphur, Arsenic, Nonmetal
  (b) Dull, Non-conductor, Brittle, Metal, Non-Metal
  (c) Iron,Zinc, Magnesium, Copper, Sodium
  (d) Sulphur, Phosphorous, Graphite, Carbon
  (e) Zinc Oxide, Sodium Oxide, Magnesium Oxide, Calcium Oxide

(a) Arsenic (Reason: Arsenic is a metalloid while remaing ones are non-metals)
(b) Metal (Reason: Rest are properties of Non-Metal)
(c) Copper (Reason: Rest are in order from least reactive to most reactive.)
(d) Graphaite: (Reason: Graphite is an allotrope (type of) of Carbon)
(e) Zinc Oxide (reason: Zinc needs strong heating to form Zinc Oxide while others form oxide at room temperature or little heating.)

Q17: Why are metals/alloys used for making bells?

Answer: Metals and Alloys (containing metal in large and non-metal in small quantity) are sonorous i.e. they give ringing sound when struck hard. Therefore metals/alloys are used for making bells.

Q18: Our body needs iron. Certain foods are rich in iron and iron tablets are recommended by doctors. But neither the food nor the tablets are hard like iron. Explain?

Answer: Iron in food supplements and in tablets is in soluble form and hence can be taken in.

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