Exploring Substances: Acidic, Basic, and NeutralClass 7 Science NCERT Solutions
12 Solutions
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Solution 1 of 12
Q1Let Us Enhance Our Learning
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
Solution
The correct answer is (iii) Vinegar.
Vinegar is an acidic solution. A solution that turns red litmus paper to blue is basic. To reverse the change, an acidic solution needs to be added. Lime water and baking soda are basic, and common salt solution is neutral. Vinegar is the only acidic option.
Q2Let Us Enhance Our Learning
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 , and C ?
(i)
Acidic, acidic, and acidic
(ii)
Neutral, basic, and basic
(iii)
Basic, basic, and acidic
(iv)
Basic, basic, and basic
Solution
The correct answer is (iv) Basic, basic, and basic.
Solution A turns red litmus blue, indicating it is basic.
Solution B turns turmeric solution red, indicating it is basic.
Solution C turns red rose extract green, indicating it is basic.
Q3Let Us Enhance Our Learning
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.
Solution
Based on the chapter content:
Fig. 2.13: The red rose extract paper strip is red, indicating the solution is acidic.
Fig. 2.14: The red rose extract paper strip is unchanged (red rose extract colour), indicating the solution is neutral.
Fig. 2.15: The red rose extract paper strip is green, indicating the solution is basic.
Q4Let Us Enhance Our Learning
A liquid sample from the laboratory was tested using various indicators: \begin{tabular}{|l|l|l|l|}\hline Indicator & Red litmus & Blue litmus & Turmeric \hline Change & No change & Turned red & No change in colour \hline\end{tabular} Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.
Solution
The liquid sample is acidic.
Justification:
Red litmus showed no change, which means it is not basic.
Blue litmus turned red, which is a characteristic of acidic solutions.
Turmeric showed no change, which is expected for acidic or neutral solutions. Since blue litmus turned red, it confirms the solution is acidic.
Q5Let Us Enhance Our Learning
Manya is blindfolded. She is given two unknown solutions to test and determine whether they are acidic or basic. Which indicator should Manya use to test the solutions and why?
Solution
Manya should use an olfactory indicator. Olfactory indicators are substances whose odour changes in acidic or basic media. Since Manya is blindfolded, she cannot rely on visual indicators like litmus paper or red rose extract. Olfactory indicators like onion or vanilla extract would allow her to differentiate between acidic and basic solutions based on the change in their smell.
Q6Let Us Enhance Our Learning
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.
Solution
One possibility is to use a turmeric solution for the spraying liquid and a soap solution for writing on the paper.
| Writing Material | Spray Bottle Contents | Colour of Writing |
|---|---|---|
| Soap solution | Turmeric solution | Red |
| Baking soda solution | Turmeric solution | Red |
| Vinegar | Red rose extract | Red |
| Lemon juice | Red rose extract | Red |
Q7Let Us Enhance Our Learning
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.
Solution
If baking soda is added to the mixture of grape juice and red rose extract, the mixture will turn green.
Justification: Grape juice is acidic, so the red rose extract will give a red tint. Baking soda is basic. Adding a base to an acidic solution containing red rose extract will cause the extract to change colour from red to green.
Q8Let Us Enhance Our Learning
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?
Solution
To reveal the message written with orange juice, the grandmother can use turmeric paper as an indicator.
Orange juice is acidic. The message can be revealed by spraying a basic solution, like soap solution, over the paper. The turmeric paper will turn red where it comes into contact with the basic solution, making the message visible.
Q9Let Us Enhance Our Learning
How can natural indicators be prepared? Explain by giving an example.
Solution
Natural indicators can be prepared from substances found in nature, such as flowers, vegetables, and spices. These indicators change colour in the presence of acidic or basic substances.
Example: Red rose extract can be prepared by crushing red rose petals and immersing them in hot water. The water will become coloured, and this coloured water can be used as an acid-base indicator. It turns red in acidic solutions and green in basic solutions.
Q10Let Us Enhance Our Learning
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.
Solution
Yes, they can be identified using turmeric paper.
- Dip the turmeric paper into each of the three liquids.
- Vinegar is acidic, so it will not change the colour of the turmeric paper.
- Baking soda solution is basic, so it will turn the turmeric paper red.
- Sugar solution is neutral, so it will not change the colour of the turmeric paper.
Therefore, the liquid that turns the turmeric paper red is baking soda solution, and the other two can be distinguished by tasting them (under supervision). Vinegar has a sour taste, while sugar solution has a sweet taste.
Q11Let Us Enhance Our Learning
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?
Solution
The nature of liquid X will be basic.
When excess amla juice is added to liquid X, the green colour of the red rose extract will eventually change to red. This is because amla juice is acidic and will neutralize the basic solution, eventually turning it acidic.
Q12Let Us Enhance Our Learning
Observe and analyse the information given in the following
Solution
This question is incomplete, as it refers to information that is not included in the provided text. Therefore, it is not possible to provide a solution.