Jaswanth
Chapter
11
CHEMICAL REACTIONS
153
CHAPTER 11
11. Chemical Reactions
All living beings born in this beautiful world have their own life styles. Have you observed and analyzed your daily life from the view point of a chemist? Chemical reactions happen around us all the time and even in our body. Any change can be classified as physical change and chemical change. Physical changes can be easily reversed but, it is not easy to reverse a chemical change. What is the reason? In chemical changes, new substances are formed and it is difficult to regenerate the original substances. Chemical changes are more permanent than physical changes. All chemical changes are accompanied by chemical reactions. How do we come to know that a chemical reaction has taken place? Let us perform some activities to find out the answer to this question. The lustrous white colour of the silver anklet slowly changes into slightly black colour. That is, silver anklet has got
Fig. 11.1 Silver Anklet
tarnished. Can you guess the reason behind it? It is due to the formation of silver sulphide (Ag2S), as a result of the reaction between silver and hydrogen sulphide in the air.
ACTIVITY 11.2
• • Take lead nitrate solution in a beaker Take potassium iodide solution in a test tube.(Both solutions are colourless) Add potassium iodide solution slowly to the lead nitrate solution What do you observe?
ACTIVITY 11.1
•
CHEMISTRY
Look at the new silver anklet of your mother or sister Note the colour of the anklet Observe the colour of an old anklet What change do you observe?
• • •
• •
154
CHEMICAL REACTIONS
You observe a deep yellow precipitate, don’t you? Do you observe any brisk effervescence? It is due to the evolution of carbon dioxide gas.
Lead iodide.
brisk effervescence
Fig. 11.2 Yellow precipitate of lead iodide.
It is lead iodide (pbI2).
Fig. 11.3 Reaction of calcium carbonate with dil.HCl
ACTIVITY 11.3
• • • • Take 5g of calcium
11
CHEMICAL REACTIONS
153
CHAPTER 11
11. Chemical Reactions
All living beings born in this beautiful world have their own life styles. Have you observed and analyzed your daily life from the view point of a chemist? Chemical reactions happen around us all the time and even in our body. Any change can be classified as physical change and chemical change. Physical changes can be easily reversed but, it is not easy to reverse a chemical change. What is the reason? In chemical changes, new substances are formed and it is difficult to regenerate the original substances. Chemical changes are more permanent than physical changes. All chemical changes are accompanied by chemical reactions. How do we come to know that a chemical reaction has taken place? Let us perform some activities to find out the answer to this question. The lustrous white colour of the silver anklet slowly changes into slightly black colour. That is, silver anklet has got
Fig. 11.1 Silver Anklet
tarnished. Can you guess the reason behind it? It is due to the formation of silver sulphide (Ag2S), as a result of the reaction between silver and hydrogen sulphide in the air.
ACTIVITY 11.2
• • Take lead nitrate solution in a beaker Take potassium iodide solution in a test tube.(Both solutions are colourless) Add potassium iodide solution slowly to the lead nitrate solution What do you observe?
ACTIVITY 11.1
•
CHEMISTRY
Look at the new silver anklet of your mother or sister Note the colour of the anklet Observe the colour of an old anklet What change do you observe?
• • •
• •
154
CHEMICAL REACTIONS
You observe a deep yellow precipitate, don’t you? Do you observe any brisk effervescence? It is due to the evolution of carbon dioxide gas.
Lead iodide.
brisk effervescence
Fig. 11.2 Yellow precipitate of lead iodide.
It is lead iodide (pbI2).
Fig. 11.3 Reaction of calcium carbonate with dil.HCl
ACTIVITY 11.3
• • • • Take 5g of calcium