RBSE Class 7 Science Chapter 2 Question Answer Exploring Substances Acidic Basic and Neutral

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Exploring Substances Acidic Basic and Neutral Class 7 Question Answer

RBSE Class 7 Science Chapter 2 Exploring Substances Acidic Basic and Neutral Question Answer

Class 7 Science Curiosity Chapter 2 Question Answer (Exercise)

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Question 1.
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

Question 2.
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?
(i) Acidic, acidic, and acidic
(ii) Neutral, basic, and basic
(iii) Basic, basic, and acidic
(iv) Basic, basic, and basic
Answer:
(iv) Basic, basic, and basic

Question 3.
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.

Answer:
Red rose extract paper strips are used in Fig. 2.13, 2.14 and 2.15. Nature of solution present in each of the containers is
Fig. 2.13, colour changed to green — Basic
Fig. 2.14, no colour changed — Neutral Fig.
2.15, colour changed into red — Acidic.

Question 4.
A liquid sample from the laboratory was tested using various indicators:

Indicator	Red litmus	Blue litmus	Turmeric
Change	No change	Turned red	No change in colour

Based on the tests, identify the acidic and basic nature of the liquid and justify your answer.
Answer:
Experiment
Red litmus No change → acidic nature
Blue litmus → Red → acidic solution
Turmeric → No change in colour → acidic solution

Question 5.
Manya is blind folded. 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?
Answer:
Manya is blind folded, so to test the solutions she should use olfactory indicators. They change smell in an acidic or basic medium.

Question 6.
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.
Answer:
A solution which changes colour can be used for writing the message on the white sheet of paper. For writing on paper soap solution and in spray bottle turmeric solution. Because soap solution is basic in nature which changes colour of turmeric solution and turmeric solution, which is yellow turn red when comes in contact with basic solution.
Table for writing colours

Solution used for writing	Solution used in spray bottle	Observed colour
Soap solution	Turmeric solution	Red/Brown
Lemon juice	Hibiscus flower extract	Dark pink colour
Baking soda solution	Turmeric solution	Red

Question 7.
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.
Answer:
Grape juice is acidic in nature, gives red colour with red rose extract and when we add baking soda which is basic in nature, then it will change the mixture in basic by neutralising it.
Result : Red rose extract turn green from red colour.
Reason : Red rose extract changes into red in acidic medium and green in basic medium.

Question 8.
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?
Answer:
Orange juice is acidic in nature and rose extract give red colour in acidic medium and green colour in basic medium.
If the secret message is wrote with an acidic solution then it needs an indicator which changes colour with acids. So spraying rose extract on secret message will change in red colour and reveal the message.

Question 9.
How can natural indicators be prepared? Explain by giving an example.
Answer:
Natural indicators are the material which shows different colours in acidic and basic solutions. They are obtained with flowers, leaves and other colourful parts of a plant.
Example :
Red – rose extract: By soaking petals in water and grinding them.
It shows:
In acidic medium – Red colour
Basic medium – Green colour

Turmeric papers : By dipping paper in turmeric paste and drying.
It changes:
In basic medium – Yellow to red
Acidic medium – No change

Juice of red cabbage: By chopping and then boiling in water.
It shows:
In acidic medium – Red/pink
Basic medium – Green/yellow.

Question 10.
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.
Answer:
Turmeric paper turns into red/brown colour from yellow colour in basic medium.
In vinegar (Acidic medium) – No change in colour
Baking soda solution (Basic medium) – Turns red/brown
Sugar solution (Neutral) – No change in colour. So. it gives the same reaction with acidic and neutral solution hence we can’t identify them only using turmeric paper.

Question 11.
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?
Answer:
Red- rose extract changes into green colour in basic medium. So if extract changes into green means liquid X is of basic nature. If the basic liquid X is added into amla juice extract, w hich is acidic in nature, it will neutralise the basic liquid X.

Question 12.
Observe and analyse the information given in the following flowchart. Complete the missing information.

Answer:
(i) Acidic
(ii) Basic
(iii) Red/blue litmus, natural indicators like Red cabbage, Red rose extract
(iv) Lime water/calcium hydroxide
(v) Organic substance/compost

Dive Deeper
Question. Aman 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?
Answer:
There is calcium carbonate (CaCCfy) present in eggshell and marble. Vinegar is acidic in nature, which releases C00 gas in bubble form after reacting with calcium carbonate. Soap solution is basic in nature, which does not release gas, so bubbles does not formed.

Exploring Substances Acidic Basic and Neutral Class 7 Questions and Answers (Intext)

(Page No. 7)

Question 1.
In science fair entrance, after receiving white paper sheet, why the message appeared after spraying liquid?
Answer:
The hidden message appeared after spraying liquid on paper because an indicator was used in writing of message which shows colour after reacting with acid or base.

(Page No. 10)

Question 2.
What are these red and blue litmus paper strips made of? Why do they change colour when drops of some samples are put on them?
Answer:
itmus is a natural substance obtained from lichens. They turn blue litmus into red in acidic solution and red litmus into blue in basic solution. So the drops are may be acid or base.

(Page No. 11)

Question 3.
If litmus is not available, are there some other natural substances that can serve as acid- base indicators?
Answer:
Yes, there are many other natural substances which shows characteristic of indicators are Turmeric, red rose, hibiscus etc.

(Page No. 16)

Question 4.
Are there any substances whose odours change on adding acidic or basic substances?
Answer:
Yes, there are some substances whose odours change in acidic or basic medium. These are called olfactory indicators.