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Acids and Bases Class 7 Questions and Answers Notes
Class 7 Basic Science Chapter 2 Acids and Bases Question Answer Pdf
Basic Science Class 7 Chapter 2 Question Answer Kerala Syllabus
Let Us Assess
Question 1.
Which among the following can be used as an indicator of acid?
a. Turmeric
b. Pathimugam
c. Red litmus paper
d. Phenolphthalein
Answer:
Red litmus paper is the most suitable indicator
Question 2.
Which acid is used in automobile batteries?
a. Hydrochloric acid
b. Nitric acid
c. Sulphuric acid
d. Formic acid
Answer:
c. Sulphuric acid
Question 3.
Among the liquids in the three beakers placed on the table, the first one is water, the second is an acid, and the third is a base. Is it right to identify them by touching, tasting or smelling? Why? Suggest a method to identify each of them.
Answer:
Many acids and bases can cause chemical burns or skin irritation. Tasting unknown substances is extremely dangerous. Acids and bases can cause severe damage to the mouth, oesophagus, and stomach. Inhaling vapours from acids and bases can irritate or damage the respiratory system. Water: Neutral litmus paper will show no colour change.
Acid: Red litmus paper will stay red, but blue litmus paper will turn red.
Base: Blue litmus paper will stay blue, but red litmus paper will turn blue.
Another method for acids: Add a small amount of baking soda to each liquid. Acids will react with baking soda to produce carbon dioxide gas, which will bubble.
Another method for bases: Add a few drops of phenolphthalein to each liquid. It will turn pink in basic solutions and remain colourless in neutral or acidic solutions.
Question 4.
In the laboratory, metallic caps are not used for glass bottles containing acids. Explain the reason for this.
Answer:
Acids can react with metals to form salts and release hydrogen gas. This reaction can corrode the metallic cap. To avoid the problems associated with corrosion, safety hazards, and compatibility issues, non-metallic caps (such as those made of plastic or other inert materials) are preferred for sealing glass bottles containing acids.
Question 5.
Examine the statements given below. Classify them on the basis of the properties of acids and bases.
a. Has a sour taste
b. Turns to pink when phenolphthalein is added
c. Slippery
d. Turns to pink when methyl orange is added
e. Turns the colour of Pathimugam water into yellow
f. Red litmus turns blue
g. Reacts with metals to produce hydrogen
h. Has an alkaline taste
Answer:
Properties of acids:
- Has a sour taste.
- Turns the colour of Pathimugam water into yellow.
- Reacts with metals to produce hydrogen.
Properties of bases:
- Turns to pink when phenolphthalein is added.
- Slippery
- Red litmus turns blue.
- Has an alkaline taste.
Question 6.
You have learnt about various indicators to identify acids and bases. Complete the table below.
Answer:
Class 7 Basic Science Chapter 2 Extended Activities Answers
Question 1.
You have identified the colour changes produced in acids and bases when various natural indicators and indicators used in the laboratory are added to them. Use this information to design science magic and present it in your class as well as in the Science Club. After the presentation, explain the scientific principle behind the magic.
Answer:
A. Red Cabbage Juice Magic:
Procedure: Show the class a beaker of red cabbage juice. Add a few drops of HCl to one part and NaOH to another part.
Result: The cabbage juice will turn red with HCl and green/blue with NaOH.
Explanation: Red cabbage contains anthocyanins, which are natural pH indicators that change colour depending on the acidity or basicity of the solution.
B. Turmeric Solution Trick:
Procedure: Dip a piece of paper into the turmeric solution and let it dry. Divide it into two pieces. Add a drop of HCl to one piece and a drop of NaOH to the other.
Result: The turmeric paper will remain yellow with HCl and turn reddish-brown with NaOH. Explanation: Turmeric contains curcumin, which turns reddish-brown in basic environments and remains yellow in acidic environments.
C. Hibiscus Petal Extract Show:
Procedure: Show the class the hibiscus extract in a beaker. Add HCl to one part and NaOH to another.
Result: The extract will turn pink/red with HCl and greenish with NaOH.
Explanation: Hibiscus petal extract contains anthocyanins, which respond to pH changes by altering colour.
Question 2.
You have understood that hydrogen is released when acids react with metals. Using this
Answer:
Materials Needed: Hydrochloric acid (HCl) solution (dilute), Zinc granules or aluminium foil, a small flask or test tube, a balloon, and a funnel.
Procedure: Place a small amount of zinc granules or crumpled aluminium foil into the flask or test tube. Using the funnel, carefully pour a small amount of dilute hydrochloric acid into the flask or test tube with the zinc or aluminium. Quickly cover the opening of the flask or test tube with the balloon to capture the gas that is produced.
As the acid reacts with the metal, hydrogen gas will be released and will start to fill the balloon. Once the balloon is sufficiently filled with hydrogen gas, carefully remove it from the flask or test tube. Inference: When an acid reacts with a metal, it produces hydrogen gas. Hydrogen is a colourless, ’ odourless gas that is lighter than air, which allows the balloon filled with hydrogen to rise and float.
Class 7 Basic Science Chapter 2 Intext Question and Answers
Question 1.
Haven’t you read Jinu’s diary entry? What could be the secret behind the experiment conducted by the teacher in Jinu’s class?
Answer:
Yes. The pink liquid in the first tumbler was probably a pH indicator solution. One common pH indicator that appears pink in basic solutions is phenolphthalein. The second tumbler, which appeared empty, likely contained a colourless acidic solution, such as vinegar (acetic acid) or lemon juice (citric acid). When the pink basic solution was poured into the acidic tumbler, the acid neutralised the base. This caused the pH to drop below the threshold, where phenolphthalein remains pink, turning it colourless or a different colour if another indicator was present.
Question 2.
Take out the glass tumblers from your Science Kit and arrange them on the desk. Add two or three drops of vinegar, tamarind water, lemon juice, salt the solution, ash suspension and baking soda solution into separate tumblers. Pour half a glass of pathimugam water into each tumbler. Does the water in any of the tumblers turn yellow? What is your observation? Record it in your Science Diary.
Answer:
Materials required: Glass tumbler, vinegar, lemon juice, salt solution, ash suspension, baking soda solution, Pathimugam water.
Procedure: We have to prepare several glass tumblers with vinegar, lemon juice, salt solution, ash suspension, and baking soda solution and then add pathimugam water to each. Here, pathimugam water will act as a natural indicator.
Observation:
1. Vinegar: Pathimugam water turned yellow. (Acidic)
2. Tamarind Water: Pathimugam water turned light yellow. (Acidic)
3. Lemon Juice: Pathimugam water turned pale yellow. (Acidic)
4. Salt Solution: No significant colour change. (Neutral)
5. Ash Suspension: Pathimugam water turned to a different shade. (Basic)
6. Baking Soda Solution: Pathimugam water changed colour. (Basic)
Inference: The colour change in pathimugam water depends on the pH of the added solution. Acidic solutions tend to turn the water yellow, while basic solutions cause different colour changes.
Question 3.
In the experiment mentioned in Jinu’s diary, the teacher must have added something to the second tumbler. Which among the following did the teacher add to turn the pink liquid into yellow? Put a tick (V) mark on the appropriate boxes, based on the experiment you have done.
Answer:
Question 4.
Do the substances that turned pathimugam water into yellow have anything common in their taste?
Answer:
They all have a sour taste. The sour taste is due to the presence of some acids in them.
Question 5.
Let’s do some more experiments to know the properties of acids. Place everyone’s glass tumblers on the desk. Fill a half portion of each glass with a different liquid from the list given below.
- Soap water
- Lemon juice
- Clear baking soda solution
- Clear lime water
- Vinegar
- Buttermilk
- Tamarind water
- Clear ash suspension
Question 6.
Take blue and red litmus papers from the school laboratory. Dip blue and red litmus papers in these liquids. Tabulate your observations in the Science Diary.
Answer:
Materials required: Glass tumbler, Soap water, Lemon juice, Clear baking soda solution, Clear lime water, Vinegar, Buttermilk, Tamarind water, Clear ash suspension, Red and blue litmus paper.
Procedure: Place everyone’s glass tumblers on the desk. Fill a half portion of each glass with different liquids. Take blue and red litmus papers from the school laboratory. Dip blue and red litmus papers in these liquids.
Observation:
Inference: Lemon juice, vinegar, buttermilk, and tamarind water turned blue litmus paper red and did not change red litmus paper. Soap water, clear baking soda solution, clear lime water, and clear ash suspension turned the red litmus paper blue and did not change the blue litmus paper. This experiment shows the effectiveness of litmus paper in identifying the acidic or basic nature of different substances.
Question 7.
Which liquids turned blue litmus into red?
Answer:
Lemon juice, vinegar, buttermilk, and tamarind water.
Question 8.
Which liquids turned red litmus into blue?
Answer:
Soap water, clear baking soda solution, clear lime water, and clear ash suspension.
Question 9.
Classify the liquids you have experimented into acids and bases. Record it in the Science Diary.
Answer:
| Acids | Bases |
| Lemon juice | Soap water |
| Vinegar | Clear baking soda solution |
| Buttermilk | Clear lime water |
| Tamarind water | Clear ash suspension |
Question 10.
Rub a red Hibiscus flower thoroughly on both sides of a white paper. What is the colour of the paper now? Didn’t the colour of the paper change? This paper can be tested on the liquids in the Science Kit. Record your observations in the Science Diary.
Answer:
The colour of paper rubbed with hibiscus flower is pink colour.
Question 11.
Observe the change in colour when two or three drops of Phenolphthalein are added to various acids and bases. Similarly, add two or three drops of Methyl Orange in acids and bases and observe the change. Tabulate the colour change.
Answer:
Question 12.
Which substances can be used as indicators of acids?
Answer:
Litmus Paper, Methyl Orange, phenolphthalein
Question 13.
Which substances can be used as indicators of bases?
Answer:
Turmeric, Litmus Paper, Methyl Orange, phenolphthalein
Question 14.
You have now realised that acids turn blue litmus into red, and bases turn red litmus into blue. Do they have any other common properties?
Answer:
They can neutralise each other, conduct electricity, and are often corrosive. These properties make them important in a wide range of chemical reactions and practical applications.
Question 15.
Dip your fingers in each liquid in the Science Kit and rub the fingers as shown in the picture. Which liquids feel slippery? List them.
Answer:
Soap water
Clear baking soda solution Clear lime water Clear ash suspension.
Question 16.
You have now identified the common properties of acids and bases. Tabulate them.
Answer:
| Acids | Bases |
| Sour taste | Bitter taste |
| Turn blue litmus red | Turn red litmus blue |
| React with metals to form hydrogen | Slippery |
| React with carbonates to form carbon dioxide. | Reacts with oxides and hydroxides to form water and salts. |
Question 17.
Which among the following substances can turn blue litmus red? List them.
- Orange juice
- Rice soup
- Black tea
- Bilimbi (Irumban puli) juice
- Grape juice
- Tomato juice
- Coconut water
Answer:
Orange juice
Black tea
Bilimbi (Irumban Puli) juice
Grape juice
Tomato juice
Question 18.
Now, let’s do experiments by diluting some acids and bases in the laboratory.
a) Which acids and bases can be taken?
b) Which indicators are to be taken?
c) Observe and tabulate the colour changes that occur when various indicators are added to them.
Answer:
a) Hydrochloric acid. Sulphuric acid, Sodium hydroxide. Potassium hydroxide
b) Red Litmus Paper, Blue Litmus Paper, Methyl Orange, phenolphthalein.
Question 19.
Fill a quarter of a test tube with vinegar (dilute acetic acid). Put three or four small strips of magnesium ribbon into it. Note down your observation. Close the mouth of the test tube with your thumb for a while. What do you feel? Which is the gas that bubbles up and pushes at your thumb?
Answer:
Bubbles are formed around the magnesium strips. If you close the mouth of the test tube with your thumb, you will feel pressure building up against your thumb. This is due to the gas being produced in the reaction. The gas that bubbles up and pushes against your thumb is hydrogen gas (H2).
Question 20.
How many general properties of acids have you identified from the experiments done so far? Record in the Science Diary.
Answer:
- Sour taste
- Turn blue litmus red
- React with metals to form hydrogen
- React with carbonates to form carbon dioxide.
Question 21.
You have understood that acids react with metals. Based on this, can you explain the reason for the following situations?
- Metal containers are not used to store pickles.
- Earthen vessels are commonly used to cook dishes with curd and buttermilk.
Answer:
Pickles are acidic in nature. If they are stored in metal containers, they react with metal, can cause health problems and damage pickles. So they are kept in earthen vessels, glass vessels, ceramic vessels and china clay vessels.
Earthen pots are more suitable for preparing food containing buttermilk. Buttermilk contains acid,that result in corrosion of an aluminium vessel.
What are the uses of vinegar at home?
Answer:
- Flavour Enhancer
- Used in pickling to preserve vegetables and fruits.
- Used to wash fruits and vegetables to remove pesticides and bacteria.
Question 22.
You already know the use of formic acid. Some acids and their uses are listed in the table below. Complete the list.
Answer:
Question 23.
Analyse the table and find out the following.
a) Which is the base used to make soap?
b) Which are the bases used in medicines?
Answer:
a) Sodium hydroxide, Potassium hydroxide
b) Aluminium hydroxide, Magnesium hydroxide
Question 24.
Add either soap solution or baking powder solution to the following substances.
- Paper rubbed with turmeric
- Turmeric water
- Observe the colour change.
Answer:
On adding the soap solution or baking powder solution to the turmeric water, the yellow colour of. the turmeric water changes to red or reddish-brown.
Question 25.
Is it possible to make use of coloured parts of plants to identify acids and bases? Which are the coloured parts of plants that you know? List them.
Answer:
Red spinach, Blue coloured clitoria (Sanghupushpam), Red cabbage, Beetroot, Lavender Roots.
Question 26.
Prepare either paper strips rubbed with each of the above vegetables, their juices or the coloured liquids obtained by boiling them in water. Test them with the acids available at home. Repeat the experiment with the bases also available at home. Write down the observations.
Answer:
Acids and Bases Class 7 Notes Extra Questions and Answers
Question 1.
The substances which turn blue litmus to red are?
Answer:
Acids
Question 2.
What are indicators? Write the names of indicators used in the laboratory.
Answer:
Indicators are substances that help to identify acids and bases by changing their colour. Litmus Paper, Methyl Orange, phenolphthalein.
Question 3.
How does milk turn acidic when it becomes curd?
Answer:
Curd contains a bacteria called Lactobacillus. The lactic acid that is produced when these bacteria nourish themselves with milk, gives curd its sour taste.
Question 4.
Tabulate the list of food items and acids present in them.
Answer:
| Food item | Main acid present |
| Buttermilk | Lactic acid |
| Curd | Lactic acid |
| Vinegar | Acetic acid |
| Lemon | Citric acid |
| Tamarind | Tartaric acid |
| Apple | Malic acid |
| Gooseberry | Ascorbic acid |
| Tomato | Oxalic acid |
Question 5.
How are alkalies useful to us?
Answer:
- In the manufacture of soap and detergents.
- For neutralising acids and in chemical reactions.
- In the manufacture of fertilisers.
- In the paper and pulp industry.
- For water treatment.
- In the textile industry.
- As cleaning agents.
- In medicine and in food processing.
Question 6.
The pickles we commonly use are acidic in nature. Are they stored in metal containers?
Answer:
Pickles are acidic in nature. If they are stored in metal containers, they react with metal can cause health problems and damage pickles. So they are kept in earthen vessels, glass vessels, ceramic vessels and china clay vessels.
Question 7.
Is an aluminium vessel or an earthen pot more suitable for preparing food containing buttermilk?
Answer:
Earthen pots are more suitable for preparing food containing buttermilk. Buttermilk contains acid,that result in corrosion of an aluminium vessel.
Question 8.
What could be the reason for the red colour appearing on clothes when the turmeric stain on them is washed with soap?
Answer:
Turmeric is a natural indicator. In the presence of alkali, it turns red colour. This is due to the basic characteristics of soap solution.
Question 9.
What precautions should we take to avoid accidents while handling chemicals?
Answer:
- Avoid spilling on body parts
- Don’t touch with hands
- Don’t smell
- Don’t taste
- Use a dropper while taking out acid from a bottle
- Use a holder while using a test tube
Question 10.
Strong acid spills on the body can cause burns. Why?
Answer:
Strong acids can absorb water and liberate heat. They can cause bums if they get spilled on the body. The first aid is pouring cold water on the affected area for a long time.
Question 11.
The table below shows the change in the colour of blue litmus paper in different substances.
| Substances | Colour change of blue litmus |
| Lemon juice | Turns red |
| Sugar solution | No colour change |
| Salt solution | No colour change |
| Tamarind water | Turns red |
| Pure water | No colour change |
| Buttermilk | Turns red |
| Vinegar | Turns red |
A. Analyse the table and write your inference.
B. Write a natural indicator we can use instead of blue litmus.
C. Name the acids which present in the given substances that turned blue litmus red.
Answer:
A. Lemon juice, tamarind water, buttermilk, and vinegar all turn blue litmus paper red, indicating they are acidic in nature. Sugar solution, salt solution, and pure water do not change the colour of blue litmus paper, indicating they are neutral and neither acidic nor basic.
B. A natural indicator that can be used instead of blue litmus paper is red cabbage juice.
C. Lemon Juice: Contains citric acid.
Tamarind Water:Contains tartaric acid.
Buttermilk: Contains lactic acid.
Vinegar: Contains acetic acid.
These acids are responsible for the acidic nature of these substances, causing the blue litmus paper to turn red.
Question 12.
Following are the findings of some experiments with acids.
A piece of paper rubbed with hibiscus changes colour when dipped in lemon juice.
Buttermilk, vinegar, lemon juice and tamarind have a common taste.
Bubbles form when zinc is added to vinegar.
Bubbles form when acid spills on a marble floor.
A) Examine the findings and write the general properties of acids.
B) Glass containers are suitable for storing pickles. What may be the reason?
C) Complete the table.
Answer:
A) General properties of acids
Sour taste
- Turn blue litmus red
- React with metals to form hydrogen
- React with carbonates to form carbon dioxide.
B) Glass containers are suitable for storing pickles because glass is non-reactive and does not react with the acids present in pickles.
Question 13.
A) Lemon juice – Citric acid
Tamarind – ………….(a)……………
Orange – Citric acid
Butter milk – ………..(b)………….
Vinegar – …………(c)………..
lime water – Calcium hydroxide
Soap solution – ………..(d)…………
Baking soda – …………(e)…………..
B) The substances which turn blue litmus to red are?
C) The substances that help to identify acids and alkalies are?
Answer:
a) Tartaric acid
b) lactic acid
c) acetic acid
d) Sodium hydroxide / Potassium hydroxide
e) Sodium bicarbonate
B) Acids
C) Indicators
Question 14.
A)Some substances have a caustic taste. Why? Write examples for such substances.
B) Why do some acids cause burns?
C) Some acids were spill on a table. How will you neutralise it?
Answer:
A) The alkaline content in these substances gives a caustic taste, e.g., soap, washing soda, lime water.
B) Some acids have the ability to absorb water and radiate heat; it is the ability that causes bums when acids fall on our skin, every cell has water content; the acid falling on the skin absorbs water from the cells and liberates heat, thereby causing serious bums.
C) To neutralize an acid, an alkali is added. Use some slaked lime as an alkali.
Question 15.
A) Find the acids and alkalies present in the following:
Tamarind, butter, orange, lemon, lime water
B) How alkalies can be distinguished by touching them?
C) The lemon piece is rubbed with a rusted iron knife to clean it; why?
Answer:
A) Tamarind-tartaric acid
Butter milk-lactic acid
Soap solution-sodium hydrochloride
Baking soda-sodium bicarbonate
Orange-citric acid
Lemon-citric acid
Lime water-calcium hydroxide
A) The aqueous solutions of alkalis have a slippery nature. So, if a solution has a slippery nature, then it can be understood that it is an alkali.
B) Lemon juice contains citric acid. Rust is an alkali. Therefore, rust and citric acid react with each other and remove the rust.
Question 16.
Balu tried to make a fire extinguisher with vinegar and magnesium ribbon. He directed the gas coming from the extinguisher towards a lighted candle. The candle flame burns with a low noise instead of extinguishing the flame.
A. Name the gas formed here.
B. Write any two features of this gas.
C. What change should be made in this experiment to work the fire extinguisher properly?
Answer:
A. The gas formed when vinegar (acetic acid) reacts with magnesium ribbon is hydrogen gas.
B. Hydrogen gas is a highly flammable and lightest element. It is colourless, odourless, and tasteless.
C. To make a fire extinguisher that works properly, Balu should use a chemical reaction that produces carbon dioxide (CO2) gas instead of hydrogen. Balu should use baking soda instead of Magnesium ribbon to produce carbon dioxide.
Question 17.
The following table shows the observation results of an experiment conducted in the class.
a) What properties do Sample -1 and Sample – 2 have?
b) Name two natural indicators that can be used in this experiment.
c) Find the odd one from the following
i) buttermilk
ii) soap water
iii) Vinegar
iv) Lime water
Answer:
a) The sample -1 indicates the presence of base.
Properties:
- Turns to pink when phenolphthalein is added
- Slippery
- Red litmus turns blue
- Has alkaline taste
The sample- 2 indicates the presence of acids Properties:
- Sour taste
- Turn blue litmus red
- React with metals to form hydrogen
- React with carbonates to form carbon dioxide.
b)
• Red cabbage juice
• Beetroot juice
c) ii) soap water
Question 18.
Some observations related to acids and alkalis are given below.
Solution -1
| No change in colour while adding Phenolphthalein. The colour changed into pale pink while adding Methyl orange. The colour did not change- when the solution was added to the cloth rubbed with turmeric. |
Solution – 2
| Formed pink colour while adding Phenolphthalein. Formed pale yellow colour on adding Methyl orange. Formed red colour when the solution was added to the cloth rubbed with turmeric. |
A) List out the chemical properties of solution I & solution 2 in the given table
B) Write down any two general properties of solution 2.
C) Find out the right pair from the following.
Automobile battery-: hydrochloric acid
Manufacturing of soap: caustic soda
Preparation of pickle: sulphuric acid
Manufacture of paint: caustic soda
Answer:
B) Slippery or Soapy Feel.
Turns Red Litmus Paper Blue
C) Manufacturing of soap: caustic soda.
Question 19.
A) The observation result of an experiment is given below. Identify the gases formed
B) Write the methods to identify the gases produced in this chemical reaction.
C) Name any two acids used in the laboratory instead of vinegar.
Answer:
A) i) Hydrogen
ii) Carbon dioxide
B) i) Collect a small sample of the gas in a test tube and bring a lit match or splint near the mouth of the test tube. If the gas is hydrogen, then it will bum with pop sound, ii) Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn milky.
C) Hydrochloric Acid, Sulphuric Acid
Question 20.
Observe the list of substances that are collected in the Science Corner.
• Vinegar
• Sodium Chloride
• Hydrochloric acid
• Sodium hydroxide
• Calcium hydroxide
A) Which alkali in this list is used to make soap?
B) Which of the following containers would you choose for making soap? a) Steel Bucket b) Plastic Bucket.
Give a reason for choosing these containers.
Answer:
A) Sodium Hydroxide
B) Steel bucket
Steel does not react with sodium hydroxide
C) Sodium Silicate helps in the hardening of the soap.
Stone Powder acts as fdler(increases the volume) in soap.
Acids and Bases Class 7 Notes
- Science Kit is a collection of materials that are used to conduct science experiments.
- Indicators are substances that help to identify acids and bases by changing their colour. Litmus paper is an indicator.
- All food items with a sour taste have acids in them.
- Hydrochloric acid, Nitric acid, Sulphuric acid, and Acetic acid are some of the strong acids used in the laboratory.
- Calcium hydroxide (Lime), Sodium hydroxide (Caustic soda), and Potassium hydroxide (Caustic potash) are some of the strong bases used in the laboratory.
- A large amount of heat is liberated when caustic soda dissolves in water during the preparation of soap.
- Add sodium silicate and stone powder one by one to increase the hardness and quantity of the soap.
- Colour and perfume can be added to the soap to make it more attractive and fragrant.
- Turmeric is a natural indicator. In the presence of alkali it turns red colour.