Here in this post we provided NCERT Exemplar Problem Class 7 Science Acids, Bases and Salts Chapter 5 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Acids, Bases and Salts Class 7 Exemplar full Explanation:
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Multiple Choice Questions
1.) The correct way of making a solution of acid in water is to
a) Add water to acid.
b) Add acid to water.
c) Mix acid and water simultaneously.
d) Add water to acid in a shallow container.
Answer:- b) Add acid to water.
Adding acid to water is the correct process of making solution.
2.) Products of neutralisation reaction are always
a) An acid and a base.
b) An acid and a salt.
c) A salt and water.
d) A salt and a base.
Answer:- c) A salt and water.
Neutralisation reaction always gets salt and water as products.
3.) Turmeric is neutral indicator. On adding it’s paste to acid and base separately, which colour would be observed.
a) Yellow in both acid and base.
b) Yellow in acid and red in base.
c) Pink in acid and yellow in base.
d) Red in acid and blue in base.
Answer:- b) yellow in acid and red in base.
Turmeric paste is the natural indicator. Which gives yellow colour adding in acid and red colour in the base.
4.) Phenolphthalein is a synthetic indicator and it’s colours in acidic and basic solution, respectively are
a) Red and Blue
b) Blue and Red .
c) Pink and colourless.
d) Colourless and pink.
Answer:- d) colourless and pink.
Phenolphthalein gives colourless in acidic solution and pink colour in basic solution.
5.) When the soil is too basic, plants do not grow well in it. To improve its quality what must be added to the soil?
a) Organic matter
b) Quick lime
c) Slaked lime
d) Calamine solution
Answer:- a) organic matter
Organic matter release acids in the soil which neutralise the basic soil.
6.) ‘litmus’ a natural dye is an extract of which of the following ?
a) China rose ( Gudhal )
b) Beetroot
c) Lichen
d) Blue berries ( jamun)
Answer:- c) Lichen
Litmus is an extraction of Lichen.
7.) Neutralisation reaction is a
a) Physical and reversible change.
b) Physical change that cannot be reversed.
c) Chemical and reversible change.
d) Chemical change that cannot be reversed.
Answer:- d) chemical change that cannot be reversed.
Neutralisation reaction is the chemical change that cannot be reversed . It always salt and water as products.
8.) A solution changes the colour of turmeric indicator from yellow to red. The solution is
a) Basic
b) Acidic
c) Neutral
d) Either neutral or acidic
Answer:- a) Basic
Basic solution change the colour of turmeric indicator from yellow to red.
9.) Which of the following set of substances contain acids ?
a) Grapes , lime water
b) Vinegar , soap
c) Curd , milk of magnesia
d) Curd, vinegar
Answer:- d) curd, vinegar
Curd and vinegar contains acid among the above.
10.) On adding phenolphthalein indicator to a colourless solution. No change is observed. What is the nature of this solution?
a) Basic
b) Either acidic or basic
c) Either acidic or neutral
d) Either basic or neutral
Answer:- c) Either acidic or neutral
Colourless solution may be either Acidic or neutral therefore no colour observed on adding phenolphthalein indicator.
11.) Which of the following is an acid – base indicator?
a) Vinegar
b) Lime water
c) Turmeric
d) Baking soda
Answer:- c) Turmeric
Turmeric indicator is an acid base indicator. Remaining are acids , bases and neutral substances.
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Very Short Answer Questions
12.) Look at the given reaction
Hydrochloric acid + sodium hydroxide (base) → sodium chloride + water
Sodium chloride formed in this reaction remains in solution form. Can we get solid sodium chloride from this solution?
Suggest a method (if any) .
Answer:- The given reaction is-
Hydrochloric acid+ sodium hydroxide (base)
↓
Sodium chloride+ water
Is an neutralisation reaction.
The product of these reaction is always a salt and water. Sodium chloride i.e salt from these solution can be obtained by the process of Evaporation. One of the method for evaporation is to keep in direct sunlight or heat the solution . After that we can get sodium chloride (Nacl) or salt from the solution.
13.) State whether the following statements are true or false . Correct the false statements.
a) All substances are either acidic or basic.
Answer:- False.
All substances are not only acidic or basic they can be neutral also.
b) A compound if acidic will turn all indicators red.
Answer:- false.
A acidic compound cannot turn all indicators red.
c) Lime water turns red litmus blue.
Answer:- True.
d) Common salt dissolved in water turns blue litmus red.
Answer:- False.
Common salt dissolved in water will not change any colour of the litmus paper.
e) Phenolphthalein is a neutral indicator.
Answer:- False.
Phenolphthalein is a man made indicator.
f) Calamine can be used to treat ant’s sting.
Answer:- True.
g) Lemon water is basic in nature.
Answer:- False.
Lemon water is Acidic in nature.
14.) Paheli is suffering from indigestion due to acidity. Is it advisable to give her orange juice in this situation and why ?
Answer:- For the proper digestion of food hydrochloric acid (HCl) is present in stomach in some amount . It is necessary for the digestion of the food. But whenever the level of acid increases in the stomach indigestion occurs. For the cure on indigestion we can take antacid. Cold raw milk is the best antacid for indigestion. We should neutralise the acid in the stomach, But orange juice cannot take after indigestion as it is Acidic in nature.
• Short Answer Questions
15.) Look at the figure. 5.1 which shows solutions taken in the test tubes A, B, C and D . What colour us expected when a piece of red litmus paper is dropped in each test tube ? Nature of the solutions is given on the table for your help.
Test tube | Nature of solutions | Change in colour of red litmus |
A | Neutral | |
B | Basic | |
C | Acidic |
|
D | Neutral |
Answer:-
Test tube | Nature of solution | Change in colour of red litmus |
A | Neutral | No change |
B | Basic | Turn blue |
C | Acidic | No change |
D | Neutral | No change |
16.) While playing in park . A child was stung 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:- when the wasp stung it injects Acidic liquid in the body. On injecting that Acidic liquid severe irrigation occurs. For neutralizing that acid an basic substance is needed . Baking soda is basic which can neutralise the wasp sting. While we cannot apply lemon juice because it is also Acidic in nature.
17.) Form a sentence using the following words – baking soda, ant bite , moist , effect , neutralised , rubbing .
Answer:- The appropriate sentence using the given words is –
The effect of an ant bite can be neutralised by rubbing moist baking soda.
18.) Match the following in Column I with those in column II .
Column I |
Column II |
a) Tartaric acid | i) Soap |
b) Calcium hydroxide | ii) Curd |
c) Formic acid | iii) Unripe mangoes |
d) Sodium hydroxide | iv) Ant’s sting |
e) Lactic acid | v) Lime water |
Answer:-
a) Tartaric acid → unripe mangoes
b) Calcium hydroxide → Lime water
c) Formic acid → Ant’s Sting
d) Sodium hydroxide → soap
e) Lactic acid → curd
19.) Fill in the blanks in the following sentences.
Answer:-
a) lemon juice and vinegar taste sour because they contain acids.
b) Turmeric and Litmus are naturalacid base indicator.
c) Phenolphthalein gives pink colour with lime water.
d) When an acidic solution is mixed with a basic solution, they neutralise each other forming salt and water.
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Long Answer Questions
20.) Boojho , paheli and their friend golu were provided with a test tube each containing China rose solution which was pink in colour. Boojho added two drops of solution ‘A’ in his test tube and got dark pink 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 changes on colour. Suggest the possible cause of the variation in their results.
Answer:- Each test tube contains China rose which is a indicator which turns Acidic solution into Dark pink colour and on addition of the basic solution China rose ( Gudhal ) turns green in colour, While on adding neutral solution it does not change any colour.
Thus the test tube A contains Acidic solution.
Test tube B contains basic solution, and
Test tube C contains neutral solution.
21.) Fill in the cross word given as figure 5.2 with the help of the clues provided.
Across :-
2) the solution which does not change the colour of either red or blue litmus.
4) phenolphthalein gives pink colour in this type of solution.
7) colour of blue litmus In lemon juice.
Down:-
1)It is used to test whether a substance is acidic or basic.
3) It is a natural indicator and gives pink colour in basic solution.
5)nature of ant’s sting.
6) it is responsible for increase in temperature during a neutralisation reaction.
22.) A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientists 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:- when we use too much of chemical fertilizers the quality of soil gets low. Soil does not remain able to grow high yield crops. High dose of chemical fertilizers make the soil acidic. When the soil is too Acidic or too basic plants do not grow well in that. When the soil is so basic, organic substances or compost is added to it. Due to the organic matter the quantity of acids in the soil is increases and it neutralizes the basic nature of soil.
When the soil which is too acidic, calcium oxide i.e quick lime or calcium hydroxide i.e slaked lime is added to soil . As these are bases which neutralise the acid in the soil and thus the soil gets treated.
23.) You are provided with four test tubes containing sugar solution, Baking soda solution, tamarind solution, salt solution. Write down an activity to find the nature. ( Acidic / basic / neutral) of each solution.
Answer:-
Four test tubes containing –
1) Sugar solution
2) Baking soda solution
3) TamarindSolution
4) Salt solution
For finding their nature Acidic / basic / neutral we can use litmus paper indicator in each test tube . We can use both red litmus paper and blue litmus paper to find out the nature of solutions. Acidic solution will turn red and basic solution it changesinto blue, neural solution will not change any colour of litmus paper.
24.) You are provided with three test tubes A,B and C as shown in figure 5.3 with different liquids. What will you observe when you put
a) A piece of blue litmus paper in each test tube .
b) A piece of red litmus paper in each test tube .
c) A few drops of phenolphthalein solution to each test tube.
Answer:-
Test tube | Effects on blue litmus | Effects on red litmus | Effects on phenolphthalein solution |
A | Turns red | Remain red | Colourless |
B | Remain blue | Turns blue | Pink colour |
C | Remain blue | Remain red | Colourless |
25.) Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village is flowing into the pond which probably caused the fish to die.
a) Explain why the fish were dying.
Answer:-factory waste should contain excessive level of acid or bases in the waste water. Fishes needs slightly basic or neutral water for living properly. But the factory waste water may contain excessive acid or base Due to which fishes are dying gradually.
b) If the factory waste is acidic in nature, how can it be neutralised?
Answer:- if the factory waste is Acidic in nature it can be neutralised by adding basic solution in the water.
26.) Explain two neutralisation reactions related to daily life situation.
Answer:- Neutralisation reaction is the reaction in which acid and base on mixingtogether gives salt and water.
Example in daily life situation on the neutralisation reaction are –
1) Ant Sting –
When an ant Stings it injects an acidic liquid in body . To neutralize the acidic liquid one should use the basic media such as moist baking soda on it. Baking soda is basic in nature which neutralise the ant stings acid.
2) Soil treatment –
When soil is too Acidic then it should be treated with the quick lime or slaked lime which are basic in nature neutralise the soil. If soil is too basic then compost or organic matter is added to soil with neutralise the basic soil.
3) Indigestion-
When the level of Hydrochloric acid is increased in the stomach indigestion occurs. For that antacid should be used which will be basic in nature will neutralise the HCl. For that milk of magnesia a basic substance can be used .