Nutrition in Plants
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   Nutrition in Animals
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   Fibre to Fabric
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   Heat
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   Acids, Bases and Salts
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   Physical and Chemical Changes
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   Weather, Climate and Adaptations of Animals to Climate
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   Winds, Storms and Cyclones
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   Soil
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   Respiration in Organisms
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   Transportation in Animals and Plants
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   Reproduction in Plants
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   Motion and Time
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   Electric Current and its Effects
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   Light
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   Water: A Precious Resource
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   Forests: Our Lifeline
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   Wastewater Story
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Question 1State the differences between acids and bases.
Answer:
- Acids Bases
(i) These are sour to taste. These are bitter to taste.
(ii) Acids turn blue litmus red. Bases do not change the colour of blue litmus.
(iii) Acids do not change the colour of red litmus. Bases turn red litmus blue.
(iv) With china rose indicator, these give dark pink colour. Bases give green colour with china rose indicator.
(v) Acids do not change the colour of turmeric indicator. Bases turn the colour of turmeric indicator to red.

Question 2: Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer: Ammonia is basic in nature as it turns the colour of red litmus paper to blue.

Question 3: Name the source from which litmus solution is obtained. What is the use of this solution?
Answer: Litmus solution is obtained from lichens. A natural dye extracted from lichens is dissolved in distilled water to obtain litmus solution. It is used as an indicator to distinguish between acids and bases.

Solution Colour of litmus solution
Acidic Red
Basic Blue
Neutral No change

Question 4: Is the distilled water acidic/basic/neutral? How would you verify it?
Answer: Distilled water is neutral in nature. The same can be verified by using red and blue litmus papers. Neither will show a colour change with distilled water. This proves that distilled water is neutral.
 

Question 5: Describe the process of neutralization with the help of an example.
Answer: The reaction between an acid and a base is known as neutralization reaction. In this reaction, both acid and base cancel each other’s effect. Neutralisation reaction results in the formation of salt and water. During this reaction, energy in the form of heat is
evolved.
Acid + Base → Salt + Water + Heat
For example, when sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water (H2O) are obtained.

Question 6: Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turns red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)
Answer: (i) Nitric acid turns red litmus blu