What happens to the steel benches and tables during rainy season?
Answer
Tarnishing of metal articles: This is because the iron metal comes into contact with water and oxygen, it undergoes a chemical reaction called Rusting. Shiny metal surfaces and other articles lose their shining appearance due to chemical reactions on the surface.
Chemical reaction requires a specific condition to occur. When chemical reactions take place there will be production of heat, light, sound, pressure etc.
Effects of chemical reactions are:
Biological effects
Environmental effects
Production of heat, light, sound and pressure
Evolution of gas, changes in colour and change in state.
Palanikumar is a Lawyer. He lives in a luxurious flat. Due to high rent, he wants to shift his residence to a place where he has a chemical industry nearby. There the rent is very cheap and the area is less populated also. His son Rajasekar, studying VIII, does not like this and likes to go to some other place.
A
Is Rajasekar right in his attitude?
B
Why did he refuse to go there?
C
What are the values shown by Rajasekar?
Answer
Yes, Rajasekar is more concerned about his family's health than saving money.
Rajasekar knows that the air pollution from the nearby chemical industry would be harmful and affect his family's health.
Environmentally sensitive, awareness, caring, and correct decision.
Kumar is going to build a house. To purchase the iron rods required for construction, he visited an iron and steel shop nearby. The seller showed him some iron rods which are fresh and good. He also showed him little older iron rods which are brownish in appearance. The price of fresh rods is more than the older ones. The seller also gave some offers to older ones. Kumar’s friend Ramesh advised him not to buy the cheaper rods.
A
Is Ramesh right in his suggestion?
B
Could you explain the reason for his suggestion?
C
What are the values shown by Ramesh?
Answer
Yes, Ramesh is right in his suggestion because old iron rods were rusted.
The older rods are brownish and they are rusted. Rusting destroys the quality of the iron rods and harmful for construction.
Responsible behaviour, correct decisions, caring, and awareness.
Classify the following day-to-day activities based on chemical reactions by physical contact, solutions of reactants, heat, light, electricity, and catalyst.
A
Burning of crackers during festivals
B
Fading of coloured clothes on drying under sunlight.
Do all the fruits and vegetables undergo browning? Explain.
Answer
No, not all the fruits. Enzymic browning can be observed in fruits such as apricots, pears, bananas, grapes, and avocados and vegetables such as aubergines, potatoes, lettuce. The enzyme polyphenol oxidase or tyrosinase that when in contact with oxygen catalyzes a biochemical reaction of plants phenolic compounds to brown pigments known as melanin, which results in the fruit or vegetable turning brown.
Explain the role of yeast in making cakes and buns in a bakery?
Answer
Yeast is a key ingredient in the production of baked goods.
Yeast is a bio-organic catalyst carbon dioxide is generated by the yeast as a result of the breakdown of fermentable sugars in the dough and makes cakes rise.
Tarnishing of metal articles: Shiny metal surfaces and other articles lose their shining appearance due to chemical reactions on the surface. For example, silver articles become black on exposure to atmospheric air. Similarly, brass vessels which contain copper as one of the constituents develop a greenish layer on exposure to air for a long time. This is due to a chemical reaction between copper and moist air to form basic copper carbonate and copper hydroxide.
1. Photosynthesis is a process in which light energy from the sun is used by the plants to prepare starch from carbon dioxide and water. 2. The sunlight uses the chemical reaction between carbon dioxide and water, which finally ends up in the production of starch (photo means light and synthesis means production). These chemical reactions used by light are called photochemical reactions.