Observing the changes, in which of the following would you say a chemical reaction may be occurring?
(i) Heating iodine changes the colour from bluish black to purple.
(ii) Mixing ammonia and hydrogen chloride gases gives fumes containing a white powdery substance.
(iii) Mixing an acid and a base solution raises the temperature.
(iv) Mixing ferrous sulphide and hydrochloric acid gives off a gas with a rotten egg smell.

(i), (ii), (iii)

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(i), (ii), (iv)

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(ii), (iii), (iv)

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(i), (ii), (iii), (iv)

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Solution

The correct option is D (i), (ii), (iii), (iv)
If you were observing only the changes without knowing the underlying reaction, all four of the given events may be chemical reactions because:
(i) Colour change occurs
(ii) Change of state has happened from gas to solid
(iii) Change in temperature has occurred
(iv) A gas has been released

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Similar questions

By observing the mentioned events below, which of the following shows chemical change?
(i) Heating iodine changes the colour from bluish black to purple
(ii) Mixing ammonia and hydrogen chloride gases gives fumes containing a white powdery substance
(iii) Mixing an acid and a base solution raises the temperature.
(iv) Mixing ferrous sulphide and hydrochloric acid gives off a gas with a rotten egg smell

Name the following:
(i) Acid present in the stomach of mammals.
(ii) Drying agent used to dry hydrogen chloride.
(iii) Salt obtained by heating sodium chloride with concentrated sulphuric acid below 200 degree celsius.
(iv) Gas that yields dense white fumes when mixed with hydrogen chloride.
(v) Two solution that yield white precipitates, when treated with hydrogen chloride or hydrochloric acid.
(vi) Gas obtained by treating metals with hydrochloric acid.
(vii) Gas obtained by treating ferrous sulphide with hydrochloric acid.
(viii) Five oxidizing agents that liberate chlorine from concentrated hydrochloric acid.
(ix) Acid used to extract glue from bones.
(x) A chloride which is soluble in excess of ammonium hydroxide.
(xi) A greenish yellow gas.
(xii) A chemical in which gold can be dissolved.
(xiii) A metallic oxide which reacts with hydrochloric acid to give a coloured solution.
(xiv) Two colourless gases which when mixed produce a white solid.

Q. Observing the changes, in which of the following would you say a chemical reaction may be occurring?

_{A drop of water is poured over a white powdery substance. Then it is observed that the substance turns blue. Answer the following questions :}

_{(i) What is the white powdery substance?}

_{(ii) Why does the substance change to blue colour?}

_{(iii) Write the chemical formula of the blue substance .}

_{(iv) Is the blue substance an acidic salt or a basic salt?}

_{(v) Give a reason for your answer in (iv).}

Q. Match the following:

	Column A	Column B
1.	A substance that turns moist starch iodide paper blue.	A. Ammonium sulphate
2.	A compound which releases a reddish brown gas on reaction with concentrated sulphuric acid and copper turnings.	B. Lead carbonate
3.	A solution of this compound gives a dirty green precipitate with sodium hydroxide.	C. Chlorine
4.	A compound which on heating with sodium hydroxide produces a gas which forms dense white fumes with hydrogen chloride.	D. Copper nitrate
5.	A white solid which gives a yellow residue on heating.	E. Ferrous sulphate.

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