Page 68 - Let us Enhance our Learning
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1. Match the fruits with the acids naturally present in them.
A Ans B P. Orange ( 2 ) 1. Tartaric acid Q. Amla ( 3 ) 2. Citric acid R. Tamarind ( 1 ) 3. Ascorbic acid and citric acid S. Tomato ( 4 ) 4. Citric acid and oxalic acid -
2. Define the following.
a) acid-base indicators: Substances that show different colours in acidic and basic solutions are called acid-base indicators.
b) neutralisation: A reaction in which an acid and a base mix in sufficient quantity to form salt and water with the evolution of heat, resulting in a solution that is neither acidic nor basic.
c) olfactory indicators: Substances whose odours change in an acidic or basic medium are called olfactory indicators. -
3. Write any two characteristics each of Acid and Base.
Characteristics of Acids:
1. They taste sour.
2. They turn blue litmus paper to red.
Characteristics of Bases:
1. They feel soapy or slippery to touch.
2. They turn red litmus paper to blue. -
4. One of your friends has been suffering from indigestion and heartburn after eating a spicy meal. To relieve the problem, he has taken a tablet. Which of the following is the most likely active ingredient in the tablet?
Answer: B: Magnesium hydroxide
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5. How can natural indicators be prepared? Explain by giving an example.
Natural indicators can be prepared using natural substances like flowers or vegetables. For example, a red rose indicator can be prepared by washing fallen red rose petals, crushing them with a mortar and pestle, placing them in a glass tumbler with hot water until the water becomes coloured, and filtering the liquid to get the flower extract.
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6. Ravi was playing near a field when a red ant bit his ankle. He felt a sharp stinging pain, and the skin around the bite turned red. His grandmother immediately applied a paste made from a household substance, and Ravi felt relief after some time. Which of the following best explains why the paste helped reduce the pain?
Answer: D. The paste neutralised the acidic substance injected by the ant
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7. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
(i) Lime water (ii) Baking soda (iii) Vinegar (iv) Common salt solution
Answer: (iii) Vinegar
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8. You are provided with three unknown solutions labelled A, B, and C, but you do not know which of these are acidic, basic, or neutral. Upon adding a few drops of red litmus solution to solution A, it turns blue. When a few drops of turmeric solution are added to solution B, it turns red. Finally, after adding a few drops of red rose extract to solution C, it turns green. Based on the observations, which of the following is the correct sequence for the nature of solutions A, B, and C ?
Answer: (iv) Basic, basic, and basic
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9. Mani is blindfolded. She is given two unknown solutions to test and determine whether they are acidic or basic. Which indicator should Mani use to test the solutions and why?
Mani should use an olfactory indicator because their odours change in acidic or basic mediums, allowing her to test them by smell.
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10. Could you suggest various materials which can be used for writing the message on the white sheet of paper (given at the beginning of the chapter) and what could be in the spray bottle? Make a table of various possible combinations and the colour of the writing obtained.
Substance used for writing Substance in the spray bottle Colour of the writing obtained Turmeric paste / solution Soap solution / Lime water Red / Orange-red Soap solution / Lime water Turmeric solution / Turmeric paper extract Red / Brownish-red Red rose extract Lemon juice Red Red rose extract Soap solution Green
Page 72 - Let us Enhance our Learning (Continued)
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11. Keerthi wrote a secret message to her grandmother on her birthday using orange juice. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
We can use a natural indicator like turmeric paper or red rose extract to reveal the secret message written with orange juice.
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12. The extract of red rose turns the liquid X to green. What will the nature of liquid X be? What will happen when excess of amla juice is added to liquid X?
Liquid X is basic in nature because the extract of a red rose turns green in basic solutions. When an excess of amla juice (acidic) is added to liquid X, a neutralisation reaction takes place, and the colour of the solution will eventually change from green back to red.
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13. Observe and analyse Figs. 2.13, 2.14, and 2.15, in which red rose extract paper strips are used. Label the nature of solutions present in each of the containers.
* Fig. 2.13: Basic in nature (green colour change)
* Fig. 2.14: Neutral in nature (no change)
* Fig. 2.15: Acidic in nature (red colour change) -
14. Three liquids are given to you. One is vinegar, another is a baking soda solution, and the third is a sugar solution. Can you identify them only using turmeric paper? Explain.
Yes: baking soda solution turns turmeric paper red (basic); vinegar and sugar solution do not change its colour. To distinguish vinegar from sugar solution, place a drop of each onto red-turned turmeric paper; acidic vinegar turns it yellow, whereas neutral sugar solution causes no change.
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15. Observe and analyse the information given in the following flowchart. Complete the missing information.
* The soil can be acidic in nature.
* The soil can be basic in nature.
* Which indicator can be used to test the nature of the soil? Litmus paper / Universal indicator
* The acidic soil can be treated with lime.
* The basic soil can be treated with organic matter like manure and composted leaves.
Page 74 - Let us Enhance our Learning & Dive Deeper
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17. A liquid sample from the laboratory was tested using various indicators:
Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.Indicator Red litmus Blue litmus Turmeric Change No change Turned red No change in colour Nature: Acidic in nature.
Justification: Blue litmus paper turning red indicates an acid, while turmeric shows no change in acidic solutions. -
18. Grape juice was mixed with red rose extract; the mixture got a tint of red colour. What will happen if baking soda is added to this mixture? Justify your answer.
When baking soda (a base) is added, the colour changes from red to green because baking soda is basic in nature, and red rose extract gives a green colour in a basic medium.
Dive Deeper
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Anand accidentally spilt vinegar on some pieces of an eggshell or marble and noticed bubbling. He then poured a soap solution on another piece of eggshell or marble, but no bubbles appeared. Why did bubbles occur with vinegar but not with soap solution?
Vinegar is an acid which reacts with calcium carbonate (present in eggshells and marble) to release carbon dioxide gas causing bubbling, whereas soap solution is basic and does not produce gas with calcium carbonate.
