Get the simplified Class 7 Science Extra Questions and Class 7th Curiosity Chapter 2 Exploring Substances Acidic Basic and Neutral Important Extra Question Answer with complete explanation.
Class 7 Science Chapter 2 Exploring Substances Acidic Basic and Neutral Extra Questions
Class 7 Science Chapter 2 Extra Questions on Exploring Substances Acidic Basic and Neutral
Exploring Substances Acidic Basic and Neutral Class 7 Very Short Question Answer
Question 1.
Name the acid present in lemon juice and tomato.
Answer:
Citric acid is present in lemon juice and oxalic acid is present in tomato.
Question 2.
Is lime water an acidic or basic solution?
Answer:
Lime water (calcium hydroxide) is a basic solution.
Question 3.
Write two basic substances which we use in our daily life.
Answer:
(i) Baking soda
(ii) Soap or detergent
Question 4.
Write the name of two indicators which occur naturally.
Answer:
(i) Turmeric
(ii) Red rose
Question 5.
What is the effect of acids and bases on blue and red litmus paper?
Answer:
Acids turn blue litmus paper red, while bases turn red litmus paper blue.
Question 6.
(i) Name one indicator which turns red on adding an acid.
(ii) Name one indicator which turns red on adding a base.
Answer:
(i) Litmus (blue litmus paper)
(ii) Turmeric
Question 7.
What name is given to those substances which do not change the colour of either red or blue litmus paper?
Answer:
The solutions or substances which do not change the colour of either red or blue litmus paper are neutral.
Question 8.
Name the reaction which occurs when an acid is mixed with base.
Answer:
Neutralisation reaction.
Question 9.
Which acid is injected into our body by an ant sting that causes pain?
Answer:
The acid is formic acid which is injected into the skin of a person when an ant bites.
Question 10.
Form a sentence using the following words : baking soda, ant bite, moist, effect, neutralised, rubbing. NCERT Exemplar
Answer:
The effect of an ant bite can be neutralised by rubbing moist baking soda.
Exploring Substances Acidic Basic and Neutral Class 7 Short Question Answer
Question 1.
Write the characteristics of acids by which we can identify them.
Answer:
Characteristics of acids are
(i) They are sour in taste.
(ii) They turn blue litmus paper/solution to red.
(iii) They react with bases to form salt and water.
Question 2.
To test the presence of an acid in any substance, what methods can be used?
Answer:
Acid can be tested in any substance by the following methods
(i) Take a drop of the dilute solution of the substance on the paper strip dipped in red rose extract. If it turns red, substance is acidic.
(ii) Dip a blue litmus paper in the solution. If the colour of the litmus paper turns red, the solution is acidic.
Question 3.
While working on a science experiment in the lab, Sia found a bottle labelled “Unknown liquid”. She thought it might be an acid, but Raj suggested they should taste it to find out, but Sia was hesitated to do so. Why should they avoid tasting the unknown liquid and what can be another method to test the nature of the liquid.
Answer:
They should avoid tasting the unknown liquid because it may be harmful, toxic or may cause irritation.
They could use different indicators to test the nature of the liquid safely without tasting them.
Question 4.
Look at the figure which shows solutions taken in test tubes A, B, C and D. What colour is expected, when a piece of red litmus paper is dropped in each test tube? Nature of the solutions is given in the table for your help.
| Test tubes | Nature of solution | Change in colour of red litmus |
| A | Neutral | No change |
| B | Basic | Turns blue |
| C | Acidic | No change |
| D | Neutral | No change |
Answer:
Nature of solution is given below.
Question 5.
After carrying out the neutralisation reaction, the test tube immediately found to be somewhat hot. Explain why?
Answer:
In neutralisation reaction, heat is always evolved which raises the temperature of the reaction mixture. Therefore, if we touch the test tube immediately after the neutralisation reaction, it is found to be hot.
Acid + Base → Salt + Water (heat is evolved)
Question 6.
Explain two neutralisation reactions related to daily life situation.
Answer:
1. Soil Treatment
The soil may be acidic or basic naturally. The plants do not grow well, if the soil at a place is too acidic or too basic. Excessive use of chemical fertilizers makes the soil acidic. When the soil is too acidic, it is treated with bases like quicklime (lime) or slaked lime. These bases neutralise the excess acid present in the soil and reduce its acidic nature. If the soil is basic, organic matter called manure or compost is added to it. The organic matter releases acids which neutralises the basic nature of the soil.
2. Factory Wastes
The waste substances discharged by many factories contain acids. If these factory wastes are allowed to flow into the water bodies (like rivers, ponds, lakes, etc.) then the acid present in them will kill fish and other organisms. The factory wastes are therefore neutralised by adding basic substances before discharging them into the water bodies.
Question 7.
While playing in a park, a child was sting by a wasp. Some elders suggested applying paste of baking soda and others lemon juice as remedy. Which remedy do you think is appropriate and why?
Answer:
Wasp sting inject a liquid in the skin which is acidic in nature. Hence, baking soda is the appropriate remedy as it is basic in nature and neutralises the acid.
Question 8.
Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the wastes of a factory in their village are flowing into the pond which probably caused the fish to die.
(i) Explain why the fish were dying?
(ii) If the factory waste is acidic in nature, how can it be neutralised?
Answer:
(i) If the wastes of a factory flow into waterbodies, it can cause a threat to the lives of sea creatures. Thus, fish were dying beca use factory waste may contain acids or bases or other toxic materials.
(ii) If the factory waste is acidic in nature, it can be neutralised by adding basic substances.
Exploring Substances Acidic Basic and Neutral Class 7 Long Question Answer
Question 1.
You are provided with three test tubes A, 6 and C as shown in figure with different liquids.
What will you observe when you put
(i) a piece of blue litmus paper in each test tube?
(ii) a piece of red litmus paper in each test tube?
(iii) a few drops of red rose extract to each test tube?
Answer:
| Test tubes | Effect on blue litmus paper | Effect on red litmus paper | Effect on red rose extract in solution |
| A | Turns red | Remains red | Turns red |
| B | Remains blue | Turns red | Turns green |
| C | Remains blue | Remains red | No change |
| D | Effect on blue litmus paper | Effect on red litmus paper | Effect on red rose extract in solution |
Question 2.
Boojho, Paheli and their friend Golu were provided with a test, each containing red rose solution which was pink in colour. Boojho added 2 drops of solution ‘A’ in his test tube and got red colour. Paheli added 2 drops of solution ‘B’ to her test tube and got green colour. Golu added 2 drops of solution ‘C’, but could not get any change in colour. Suggest the possible cause for the variation in their results.
Answer:
Red rose is an acid-base indicator which shows the following changes in different mediums.
Red rose + acid → Give red colour
Red rose + base → Give green colour
Red rose + neutral → No change in colour
They got variation in their results because solution ‘A’ was acidic, solution ‘B’ was basic and solution ‘C’ was neutral which gave different results with red rose indicator.
Question 3.
Explain neutralisation reaction with the help of an example, which indicator is used in this process.
Answer:
The reaction in which an acid reacts with a base to form salt and water is called neutralisation. Acids and bases are chemically opposite substances. So, when an acid is mixed with a base, they neutralise (or cancel) the effect of each other. In this process, both the acidic nature of acid and basic nature of base are destroyed.
The solution formed is neutral, but salt produced during the reaction can be acidic, basic or neutral. Some heat is always evolved, during the reaction, which raises the temperature of the mixture.
The general reaction takes place is given as
Acid + Base → Salt + Water + Heat
Question 4.
Write any three applications of neutralisation reaction.
Answer:
The neutralisation reactions play a very important role in our everyday life. Some of the examples that involves neutralisation reaction are as follows.
1. Ant Bite
When an ant bites, it injects an acidic liquid into the skin of the person which causes burning sensation. The sting of an ant contains an acid called formic acid. The effect of the acid can be neutralised by rubbing a mild base, e.g. baking soda solution or calamine solution. Thus, being a base, baking soda solution or calamine solution neutralises the acidic liquid injected by the ant and cancel its effect.
2. Soil Treatment
The soil may be acidic or basic naturally. The plants do not grow well, if the soil at a place is too acidic or too basic. Excessive use of chemical fertilizers makes the soil acidic. When the soil is too acidic, it is treated with bases like quicklime (lime) or slaked lime. These bases neutralise the excess acid present in the soil and reduce its acidic nature. If the soil is basic, organic matter called manure or compost is added to it. The organic matter releases acids which neutralises the basic nature of the soil.
3. Factory Wastes
The waste substances discharged by many factories contain acids. If these factory wastes are allowed to flow into the water bodies (like rivers, ponds, lakes, etc.) then the acid present in them will kill fish and other organisms. The factory wastes are therefore neutralised by adding basic substances before discharging them into the water bodies.
Question 5.
A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realised that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralise the soil?
Answer:
The reason for low crop yield in farmer’s field was that the soil at a place is either too acidic or too basic. The soil may be acidic or basic naturally. The excessive use of fertilizers in the fields also makes the soil too acidic. In this case, it is treated with base such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralises the excess acid present in the soil and reduces its acidic nature.
If the soil is too basic, then decaying organic matter (called manure or compost) is added to it. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.
Exploring Substances Acidic Basic and Neutral Class 7 Case Based Questions
Question 1.
In a science experiment, Riya and her friends were given three different solutions labelled A, B, and C to test their properties. They used litmus paper to identify the nature of each solution.
• Solution A turned blue litmus paper red.
• Solution B turned red litmus paper blue.
• Solution C did not change the colour of either litmus paper.
After performing various tests, Riya also observed that when solution A was mixed with solution S, a white solid is formed. This white solid was identified as salt.
(i) Identify the nature of each solution.
(ii) What type of reaction occurred when solution A was mixed with solution 6?
(iii) Define salt in the context of acids and bases.
Answer:
(i) Solution A is an acid because it turns blue litmus paper red, solution B is a base because it turns red litmus paper blue, and solution C is neutral as it does not change the colour of either litmus paper, meaning it is neither acidic nor basic.
(ii) Neutralisation reaction.
(iii) Salt is a product formed when an acid reacts with a base.
Question 2.
Red rose is a natural indicator use for the detection of acids and bases.
The flower’s petals are put in warm water for an hour. The water, after one hour can be used as an indicator. It is light pink in neutral conditions. It turns green in basic conditions and red in acidic conditions.
Zeenat takes 10 mL of three colourless liquids in separate test tubes. She add 5 drops of red rose indicator to each test tube. The pictures show the colour of the liquid in each test tube after the addition Of indicator.
(i) Which test tube contains liquid soap?
Answer:
The test tube 2 contains liquid soap as it turned green due to basic nature of soap.
(ii) Why are red rose petals put in warm water to make the indicator?
Answer:
To make the chemicals in the petals dissolve faster, the red rose petals are put in warm to make the indicator.
(iii) Why did Zeenat add the same amount of indicator to the three test tubes?
Answer:
Zeenat added the same amount of indicator to the three test tube, so that we can compare the results effectively.
Question 3.
Priya a Class 7 student tested the nature of some common substances with the help of acid-base indicators and noted down her observations in the given table.
| Substance | Turmeric indicator | Red rose extract |
| X | Remains yellow | Red |
| Y | Red | Green |
| Z | Remains yellow | Red |
| 0 | Remains yellow | Red |
(i) What could substances X, Y, Z and 0 be respectively from the given substances?
Answer:
From the colour changes shown with different indicators, it can be conclude that the substance X is acidic, i.e. spinach juice, Y is basic, i.e. soap solution, Z is neutral, i.e. sugar solution and O is again acidic, i.e. lemon juice.
(ii) What will be the colour of substance V when reacted with red litmus solution?
Answer:
Substance ‘Y’ is basic hence, it will change the colour of red litmus solution to blue.
(iii) Give one difference between the red rose indicator and turmeric indicator.
Answer:
Difference between red rose indicator and turmeric indicator is as follows. Red rose indicator give red colour with acidic substance, while turmeric indicator gives red colour with basic substance.
Exploring Substances Acidic Basic and Neutral Class 7 Skill Based Questions
Question 1.
Three test tubes A, B and C are taken as shown in figure below. Red litmus paper was dipped in all three test tubes to test which solution is basic in nature. Identify in which test tube the red litmus paper will change its colour to blue?
Answer:
Red litmus turns blue in test tube A because baking soda is a base. Bases turn red litmus paper blues while the other test tubes contain neutral (distilled water) and acidic (lemon juice) solutions, which do not change red litmus to blue.
Question 2.
Determine which of the following solution is acidic, basic (alkaline) and neutral, by using litmus as shown below. Label the following diagram.
Answer:
(i) Neutral
(ii) Acidic
(iii) Basic(Alkaline)
Question 3.
Using the knowledge of acids and bases, write a secret message with the help of lemon juice ahd red rose solution. Explain how it works?
Hint:
Prepare a solution of lemon juice. Use this solution to write a message on a sheet of white paper with a cotton bud. Rub red rose solution over the message.
Answer:
Do yourself
Question 4.
Complete the crossword puzzle with the help of the clues given below.
Hints:
1. A substance that tastes bitter and feels soapy to touch.
2. A substance that tastes sour.
3. A natural indicator that turns red in acidic solution.
4. A chemical compound formed from the reaction between an acid and an alkali.
5. A natural indicator that turns red in alkaline solution.
6 …… acid is found in lemons and oranges.
Answer:
1. Base
2. Acid
3. Litmus
4. Salt
5. Turmeric
6. Citric
Exploring Substances Acidic Basic and Neutral Extra Questions for Practice
Question 1.
If a liquid turns blue litmus red, is it an acid, base or salt?
Question 2.
What is the colour of red rose indicator in a basic solution?
Question 3.
Why organic matter is added to the basic soil?
Question 4.
Why does a yellow curry stain on a white shirt turn red when It is washed with soap?
Question 5.
Which acid is used in the making of paneer at home?
Question 6.
What is the effect of ant bite? Explain its cure.
Question 7.
A student has the following solutions in water:
A. Soap solution
B. Lemon Juice
C. Sugar solution
What will be the effect of each solution on
(a) Blue litmus paper
(b) Red litmus paper
(C) Turmeric paper
(d) Red rose indicator
Question 8.
The wastes of many factories contain acids. Why Is it considered necessary to neutralise them before allowing the wastes to flow Into waterbodies?