SAQ for Chapter 2 Exploring Substances: Acidic, Basic and Neutral Class 7 Science NCERT
Important Questions1
Q1: What is litmus and how is it used to identify acids and bases?
Answer
Litmus is a natural material made from lichens and comes as blue and red paper strips. It helps identify substances: acids turn blue litmus paper red, and bases turn red litmus paper blue.
Litmus
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2
Q2: How is red rose extract prepared and how does it act as an indicator?
Answer
Red rose extract is made by crushing fresh rose petals, soaking them in hot water, and filtering the liquid. It changes color to red in acidic substances and green in basic substances, helping to identify them.
Red Rose Petas immersed in Hot Water
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3
Q3: What color change does turmeric paper show when it comes in contact with a base?
Answer
Turmeric paper, which is yellow, turns red when it touches a basic substance. It does not change color with acidic or neutral substances.
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4
Q4: What are olfactory indicators and give an example?
Answer
Olfactory indicators are substances whose smell changes when mixed with acids or bases. For example, a cloth soaked in onion juice loses its smell when put in acidic tamarind water or basic baking soda solution.
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5
Q5: Name two other natural indicators besides litmus and red rose extract.
Answer
Beetroot and purple cabbage are natural indicators. They change color when mixed with acidic or basic substances.
Indicators
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6
Q6: Red litmus paper is dipped in a solution; it remains red, what is the nature of the solution?
Answer
Red litmus paper when dipped in a solution, if it remains red then the nature of the solution is neutral.
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7
Q7: What are salts? Give examples.
Answer
Salts are the ionic compounds generally formed by neutralisation of an acid with base. They can be acidic, basic as well as neutral. Example acidic salts: sodium bicarbonate, basic salts: magnesium chloride, neutral salt: sodium chloride.
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8
Q8: Give examples of some acids and bases
Answer
Curd, lemon juice, vinegar, orange juice etc. are acids and baking soda, lime water etc. are bases.
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9
Q9: Define indicators along with examples.
Answer
Indicators are special type of substance that are used to taste whether a substance is acidic or basic in nature. It change the colour of acidic or basis substances when added into it. Turmeric, litmus, etc. are some natural indicators.
Turmeric as Indicator
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10
Q10: What do you mean by neutral substance, explain with examples?
Answer
The substances which are neither acidic, nor basic are called neutral substance. These substances neither turn blue litmus red nor red litmus blue, for example distilled water, sugar solution etc.
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11
Q11: Rena is trying to wash turmeric stain on her cloth with soap, she noticed the stain colour changed to red, explain why?
Answer
Turmeric is a natural indicator which when reacts with bases turns it into red colour; here soap solution is basic so it turns red.
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12
Q12: Explain why factory waste should be neutralised before disposing it into the water bodies.
Answer
The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances into it.
SAQ