NCERT Class X Science Class: Chapter –1. Chemical Reactions and Equations – Part-6

Download PDF of This Page (Size: 157K)

Question 26:

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

Answer:

When an aqueous solution of potassium chloride when mixed with silver nitrate solution an insoluble white substance formed is silver chloride .

The chemical reaction are as follows:

It is a double displacement and precipitation reaction.

Question 27:

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer:

It is a thermal decomposition reaction

Question 28:

Why do fire flies glow at night?

Answer:

Fire flies have a protein which in the presence of an enzyme undergoes aerial oxidation. This is a chemical reaction which involves emission of visible light. Therefore, fire flies glow at night.

Question 29:

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?

Answer:

Grapes when attached to the plants are living and therefore their own immune system prevents fermentation. The microbes can grow in the plucked grapes and under anaerobic conditions these can be fermented. This is a chemical change.

Question 30:

Which among the following are physical or chemical changes?

  1. Evaporation of petrol

  2. Burning of Liquefied Petroleum Gas (LPG)

  3. Heating of an iron rod to red hot.

  4. Curdling of milk

  5. Sublimation of solid ammonium chloride

Answer:

(a) Evaporation of petrol is a physical change because no new chemical substance is formed

(b) Burning of LPG is a chemical change because on burning, LPG forms

(c) Heating of an iron rod to red-hot is a physical change

(d) Curdling of milk is a chemical change because in the conversion of milk to curd, new chemical substances are formed

(e) It is a physical change, because solid vapors and no new chemical substance is formed

Therefore,

(A), (B) and (B) — are physical changes.

(B) and (D) are chemical changes

Question 31:

During the reaction of some metals with dilute hydrochloric acid, following observations were made.

  1. Silver metal does not show any change

  2. The temperature of the reaction mixture rises when aluminium is added.

  3. The reaction of sodium metal is found to be highly explosive

  4. Some bubbles of a gas are seen when lead is reacted with the acid.

Explain these observations giving suitable reasons.

Answer:

  1. Silver metal does not react with dilute

  2. The temperature of the reaction mixture rises when aluminium is added because it is an exothermic reaction.

  3. Reaction of sodium metal is found to be highly explosive because it is an exothermic reaction

  4. When lead is treated with hydrochloric acid, bubbles of hydrogen gas are evolved