Q11 of 28 Page 187

Suggest a reason for each observation given below.

i) In fireworks, powdered magnesium is used rather than magnesium ribbon.


ii) Zinc and dilute H2SO4 react much more quickly when a few drops of copper sulphate solutions are added.


iii) The reaction between magnesium carbonate and dilute hydrochloric acid speeds


up when some concentrated HCl is added.

(i) We know that the rate of a reaction depends on the surface area available for the reaction to take place. The more the surface area more will be the rate of the reaction. Powdered magnesium is having more surface area than magnesium ribbon hence powdered magnesium is used rather than magnesium ribbon in fireworks so that the rate of the reaction is more.

(ii) We know that a catalyst is a substance which increases the rate of a reaction without itself getting reacted. In the reaction of Zinc and dilute H2SO4 copper sulphate solution acts as a catalyst and increases the rate of the reaction.


(iii) The rate of a chemical reaction increases as the concentration of the reactants increases hence the reaction between magnesium carbonate and dilute hydrochloric acid speeds up when some concentrated HCl is added as by doing so we are increasing the concentration of the reactants.


More from this chapter

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9

Identify the wrong statements and correct them.

i) Sodium benzoate is used in food preservative.


ii) Nitric acid is not used as fertilizer in agriculture.


iii) Sulphuric acid is called the king of chemicals.


iv) The PH of acid is greater than 7.


v) Acetic acid is used in aerated drinks.

 10

Redox reactions are reactions during which electron transfer takes place. Here

magnesium atom transfers two electrons one each to the two chlorine atoms.


i) What are the products of this reaction?


ii) Write the balanced equation for the complete reaction.


iii) Which element is being oxidized?


iv) Which element is being reduced?


v) Write the reduction part of the reaction.

 12

Sodium hydroxide and hydrochloric acid react as shown in this equation.

NaOH + HCl → NaCl + H2O


(aq) (aq) (aq) (l)


i) Which type of chemical reaction is this?


ii) The reaction is exothermic. Explain what that means.


iii) Differentiate exothermic reaction and endothermic reaction.


iv) What happens to the temperature of the solution as the chemicals react?

 13

Take two conical flasks. Label them as I and II. Take a small amount of copper sulphate solution in the first conical flask. Take a small amount of granulated zinc in the second conical flask. Allow the copper sulphate solution to react with the zinc.

i) Name the type of reaction.


ii) Say whether the metal zinc is more reactive or less reactive.


iii) Write the complete and balanced reaction.


iv) Say whether this change is reversible or irreversible.