Page 56 - Chemistry ICSE Class IX

44 ICSE Chemistry – 9
Chlorine displaces bromine from bromides and iodine from iodides in accordance with the chemical equations,
2NaBr(aq) + Cl (aq) o 2NaCl(aq) + Br 2
2
Bromine dissolves in carbon tetrachloride to give orange
coloured layer.
2NaI(aq) + Cl (aq) o 2NaCl(aq) + I 2
2
Iodine dissolves in carbon tetrachloride to give purple
(violet) coloured layer.
Q.4. In the re ning of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal.
Write down the chemical equation of the reactions involved.
Ans. 2AgNO (aq) + Cu(s) o 2Ag(s) + Cu(NO ) (aq)
3
3 2
silver nitrate copper silver metal copper(II) nitrate
Q.5. Why will the colour of heated copper powder become black when air is passed over it?
Ans. When copper powder is heated in the presence of air, black copper oxide is formed.
2Cu(s) + O (g) o 2CuO(s)
2
copper powder in the air copper oxide
(heated) (black)
Q.6. Why is respiration considered as an exothermic reaction? Explain.
Ans. During respiration, the digested food gets oxidised and the energy is released. That is why, it is considered as an
exothermic reaction.
Q.7. A shiny brown-coloured element X on heating in air becomes black in colour. Name the element X and the black-
coloured compound formed.
Ans. An element on heating in air forms its oxide. The brownish element which forms black oxide is copper. So,
Name of the element: Copper (Cu)
Name of black compound: Copper(II) oxide, (CuO)
heat
Reaction: 2Cu(s) + O (g) o 2CuO(s)
2
copper from air copper(II) oxide
(brown) (black)
ASSIGNMENT 2

Types of reactions, Energy changes in chemical reactions,
Exothermic and endothermic reactions, Electrochemical reaction, Photochemical reactions

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