Q: How do you appreciate the role of Toothpaste in preventing the tooth decay. (1 Mark)
A: 1) Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth.
2) Using tooth pastes, which are generally basic neutralize the excess acid and prevent tooth decay.
Q: Why does water kept in a clay pot remain cool? (1 Mark)
A: 1) A clay pot is porus.
2) Water in the pot comes out of the pot through pores and stay on the outer surface of the pot.
3) The necessary heat to evaporate for these water particles is taken from the water inside the pot.
4) The water on the outer surface of the pot thus evaporates cooling the water inside the pot.
Q: Name the mirror used in car headlights? How is it arranged in the car headlight? (1 Mark)
A: 1) A concave mirror is used in car headlights.
2) When a source of light is placed at the principal focus of a concave mirror, it produces a strong parallel beam of light.
3) Thus concave mirror is used as a reflector in car (automobile) headlights.
Q: Sri Lakshmi inserted two nails in a beaker which are connected to two wires with A.C. small bulb. She has taken different solutions like Sodium hydroxide, Potassium hydroxide, Alcohol, Glucose, Hydrochloric acid and Sulphuric acid in the beaker one after another. Answer the following questions: a) Which solutions can make the bulb glow? Why? b) Categorize these as acids, bases and neutral? c) Mention what is common in acids and bases? (4 Marks)
A: a) 1) Hydrochloric acid, Sulphuric acid, Sodium hydroxide and Potassium hydroxide solutions can make the bulb glow.
2) These solutions have ions and the moment of these ions in solution helps for flow of electricity through the solution.
b) 1) Hydrochloric acid, Sulphuric acid are acids.
2) Sodium hydroxide, Potassium hydroxide are bases.
3) Glucose and alcohol are neutral substances.
c) 1) Acids produce H+ ions in solutions
2) Bases produce OH− ions in solutions.
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