Q47 of 152 Page 22

When water is added gradually to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.

(a) What could be solid X? Write its chemical formula.


(b) What could be product Y? Write its chemical formula.


(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas?


(d) Write chemical equation of the reaction which takes place on adding water to solid X.


(e) Which characteristic of chemical reactions is illustrated by this example?

(a) Solid X is Calcium oxide(CaO)

(b) Product Y is Calcium hydroxide(Ca(OH)2)


(c) Common name of Y is Lime Water.


(d) CaO + H2O → Ca(OH)2


(e) Temperature Change is shown by this reaction.



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45 The chemical equations are balanced to satisfy one of the following laws in chemical reactions. This law is known as: 46 When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution.

(a) What do you think substance X is likely to be?


(b) Name the substance which the yellow solid consists of.


(c) Which characteristic of chemical reactions is illustrated by this example ?


(d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.

 48 When metal X is treated with a dilute acid Y, then a gas Z is evolved which bums readily by making a little explosion.

(a) Name any two metals which can behave like metal X.


(b) Name any two acids which can behave like acid Y.


(c) Name the gas Z.


(d) Is the gas Z lighter than or heavier than air?


(e) Is the reaction between metal X and dilute acid Y exothermic or endothermic?


(f) By taking a specific example of metal X and dilute acid Y, write a balanced chemical equation for the reaction which takes place. Also indicate physical states of all the reactants and products.

 49 A solid substance P which is very hard is used in the construction of many buildings, especially flooring. When substance P is heated strongly, it decomposes to form another solid Q and a gas R is given out. Solid Q reacts with water with the release of a lot of heat to form a substance S. When gas R is passed into a clear solution of substance S, then a white precipitate of substance T is formed. The substance T has the same chemical composition as starting substance P.

(a) What is substance P? Write its common name as well as chemical formula.


(b) What is substance Q?


(c) What is gas R?


(d) What is substances? What is its clear solution known as?


(e) What is substance T? Name any two natural forms in which substance T occurs in nature.