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CLASS - 10 SCIENCE IMPORTANT QUESTIONS OF MARK 3   FOR BOARD EXAMINATION

QUESTION NO. 16

An ore on treating with dilute hydrochloric acid produce brisk effervescene. Name the type of ore with one example. What step will be required to obtain metal from the enriched ore ? Also write the chemical equation for reaction involved in this process.

ANSWER NO. 16

Type of ore is carbonate ore.
The following steps required to obtain pure metal from this ore.
1. Calcination, to obtain oxide of the metal.
2. Reduction, reacting the oxide of metal with carbon monoxide.
3. As a result pure metal is be obtained.
   ZnCO3 ---------------------> ZnO + CO2

  ZnO + CO --------------->  Zn+ CO2

QUESTION NO. 17

When copper powder is heated in China dish the reddish brown surface of copper powder becomes coated with a black substances.
(a) why has the black substance formed?
(b) what is this black substance ?
(c) write the chemical equation of the reaction that takes place.
(d) how can the black coating on the surface be turned reddish Brown.

ANSWER NO. 17

(a) The black colour substance is formed by the                    reaction of copper with oxygen.
(b) the black colour substance is Cuo copper ii oxide.
(C)  2Cu2 + O -----------------------> 2CuO
(d) The copper oxide does form can be reduced to its         basic metal form by reducing it with hydrogen or         carbon monoxide.

QUESTION NO. 18

When potassium iodide solution is added to a solution of Lead Nitrate in a test tube, a precipitate is formed.
(a) what is the colour of this precipitate full? Name the compound precipitated.
(b) write the balanced chemical equation for this reaction.
(c) list two types of reaction in which this reaction can be placed.

ANSWER NO. 18

(a) the resulting precipitate is lead iodide PbI2 and its bright yellow.
(b) Pb(NO) + 2KI = PbI + 2KNO
(c) 1. Precipitation reaction as a yellow coloured precipitate of lead iodide is formed.
    2. Double displacement reaction.

QUESTION NO. 19

List in tabular form three physical to chemical properties on bases with ethanol and ethanoic acid can be determined.

ETHANOL
CHEMICAL PROPERTY

  • No reaction on Litmus Paper
  • No reaction with NaHCO3

PHYSICAL PROPERTY

  • Low boiling point
  • Pleasant smell
  • Burning taste

ETHANOIC  ACID
CHEMICAL PROPERTY

  • Turns blue Litmus to red
  • React with NaHCO3 to give brisk sense of CO2

PHYSICAL PROPERTY

  • High boiling point
  • Purgent smell
  •  Sour taste

QUESTION NO. 20

(a) state two properties of Carbon which lead to a very large number of carbon compound.
(b) why does micelle form formation takes place when soap is added to water? Why micelle do not form when soap is added to ethanol.

ANSWER NO. 20

(a) the two properties of Carbon that give rise to a large number of compounds are as follows -

1. CATENATION :

It is the ability to form bonds with other atoms of carbon.

2. TETRAVALENCY :

With the valency of four, carbon is capable of bonding with four other atoms.

 (b) the molecules of soap are sodium or potassium salt of long chain carboxylic acid. The ionic and of soap interacts with water why is the carbon chain interacts with oil. The soap molecules, does form structure called micelles.
          Micelle formation does not take place in ethanol because the alkyle chain of soap becomes soluble in alcohol.

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