Page 2 - H.A.2-(Practice WS-2)

Q.6 A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by
emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues
to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.

Q.7 Give reasons for the following :
(i) All decomposition reactions are endothermic reactions.
(ii) Colour of copper sulphate solution changes when an iron nail is dipped in it.
(iii) Respiration is an exothermic reaction.

Q.8 A student heated 2g of lead nitrate in a boiling tube.
(a) What changes would be observed as a result of heating.
(b) Name the type of reaction that took place.
(c) Write the balanced chemical equation for the above reaction.

Q.9 A silver article generally turns black when kept in the open for a few days. The article
when rubbed with toothpaste again starts shining. (a) Why do silver articles turn black when
kept in the open for a few days? Name the phenomenon involved. (b) Name the black
substance formed and give its chemical formula.

Q.10 Grapes hanging on the plant do not ferment but after being plucked from the plant can
be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical
change?

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