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
(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 has taken place
(ii) Change of state from gas to solid
(iii) Change in temperature is observed
(iv) A gas has been released