Page 226 - Chemistry ICSE Class IX

214 ICSE Chemistry – 9

5. A heavy, white crystalline solid on strong heating crumbles with cracking sound. It gives reddish brown gas and a residue
which is reddish-brown when hot and yellow when cooled. Identify the solid.
Ans. The given solid is lead(ll) nitrate.
6. Mention the properties by which you will identify copper(ll) sulphate hydrate.
Ans. (i) Colour – Copper(ll) sulphate hydrate is deep blue.
(ii) Action of heat – Steamy vapour is given out and blue crystals crumble to give white powder.
(iii) Action of water on the residue – When a drop of water is placed on the white powder obtained in (ii), it turns
blue in colour.
7. What is the product formed when copper(ll) carbonate is heated? Write the chemical equation.
Ans. Copper(ll) carbonate on heating gives copper(ll) oxide (black powder) and carbon dioxide.
heat
CuCO (s) o CuO(s) + CO (g)
3 2
copper(ll) carbonate copper(ll) oxide carbon dioxide
(black powder)
8. Name a salt which on heating gives the corresponding metal.
Ans. Mercury(ll) oxide on heating decomposes to give mercury.
heat
2HgO(s) o 2Hg(l) + O (g)
2
9. Write the molecular formula and the chemical name of red lead.
Ans. Red lead : Pb O — Trilead tetraoxide
3 4
10. Ammonium dichromate is an orange-red crystalline compound. Which of the ions impart this colour to the salt?
Ans. Dichromate ion (Cr O 2– ) imparts the orange-red colour to ammonium dichromate.
2 7
11. Name two substances which undergo sublimation.
Ans. (i) Ammonium chloride (ii) Iodine
12. Write the changes which occur when zinc nitrate crystals are heated gradually from low temperature to high temperature.
Ans. The sequence of changes which occur when zinc nitrate crystals are heated is

13. Name the products formed when copper(ll) nitrate hexahydrate is heated.
Ans. Products formed are:
Copper(ll) oxide, CuO(s) Black powder
Nitrogen dioxide gas, NO (g) Reddish-brown gas
2
Water vapour, H O(v) Colourless vapour
2
14. A chocolate-brown coloured, heavy amorphous powder on heating changes to reddish-brown, gives off a colourless and
odourless gas which ignites a glowing wooden splinter, the reddish- brown colour changes to yellow when cooled, and
the test tube becomes yellowish. Identify the substance and write the chemical equation.
Ans. The given powder is lead(IV) oxide (PbO ).
2
heat
2PbO (s) o 2PbO(s) + O (g)
2 2
lead(IV) oxide lead(ll) oxide
15. An orange-red crystalline solid when heated gets decomposed producing heat, light and gases. A greenish-grey residue
is left behind. Write the chemical equation and name the main product formed.
heat
Ans. (NH ) Cr O (s) o Cr O (s) + N (g) + H O(g)
4 2 2 7 2 3 2 2
ammonium dichromate chromium(lll) oxide
(greenish-grey powder)