Important Questions Class 7 Science Chapter 5

Important Questions Class 7 Science Chapter 5 – Acids, Bases, and Salts

Class 7 Science Chapter 5 is one of the most important chapters, which teaches about Acids, Bases, and Salts found in the substances we use daily and how they are formed. Acids are sour. Examples of acidic substances are lemon, curd, vinegar, etc. Bases like baking soda are bitter in taste and soapy to the touch. Salt is formed as a result of acid and base neutralisation reactions. Furthermore, this chapter covers some important topics: acids and bases, natural indicators around us, neutralisation, and neutralisation in everyday life

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A comprehensive list of Science Class 7 Chapter 5 Important Questions is taken from the NCERT textbook, NCERT exemplars, etc., for students to help revise the topics thoroughly and score well in the examination. Our question bank of Important Questions Class 7 Science Chapter 5 is a useful tool for students to solve a lot of exam-oriented questions. The question bank comes with detailed self-explanatory solutions that will help students revise the chapter fully while solving the questions.

Important Questions Class 7 Science Chapter 5 – With Solutions

Chapter 5, Class 7, Science Important questions are extremely helpful for students preparing for CBSE examinations. The Extramarks team understands that regularly solving questions will help students revise the subject and also retain their knowledge of the topics.

Hence, our team of expert science teachers have prepared a comprehensive list of Science Class 7 Chapter 5 Important Questions including textbook exercise questions and answers, MCQs, short answer questions, and long answer questions taken from the NCERT textbook, NCERT exemplars, etc. Students should solve these important questions while revising the chapter to clarify all the doubts.

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The below-given list consists of a few questions and their answers from our Class 7 Science Chapter 5 Important Questions:

Question 1. State the differences between acids and bases with examples.

Answer 1.  

  • Acids: The acidic chemical substances are called acids. These substances taste sour—for example, curd, lemon juice, vinegar, and tamarind.
  • Bases: The nature of such substances is basic. These substances taste bitter and feel soapy on touching, for example, baking soda and milk of magnesia.

Question 2. The appropriate method of preparing an acid solution in water is, 

(a) Add water to acid.

(b) Add acid to water.

(c) Add water to acid in a shallow container.

(d) Mix acid and water simultaneously

Answer 2. (b) Add acid to water.

Explanation: Adding water to a concentrated acid releases a huge amount of heat due to an exothermic reaction and leads to explosions. Hence, adding acid to water is the correct way to make a solution of acid.

Question 3. Give any two names of the indicators that occur naturally.

Answer 3.  

  • Litmus
  • China Rose

Question 4. Explain the neutralisation process with the help of an example.

Answer 4. A basic solution is mixed with an acidic solution in the neutralisation process.

The resulting solution is neither acidic nor basic,, as both the acidic nature of the acid and the basic nature of the base are destroyed. Water and salt are produced in this process with the evolution of heat.

Below is an example of neutralisation

Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)

Question 5. State whether the below-given statements are true or false. Correct the false statements.

(a) A compound, if acidic, will turn all indicators red.

(b) All the substances are either acidic or basic.

(c) Common salt dissolved in water turns blue litmus red.

(d) Lime water turns red litmus blue.

(e) Phenolphthalein is a natural indicator.

(f) Calamine can be used to treat ant stings.

(g) Lemon water is basic.

Answer 5. 

  1. False. Acidic compounds will not turn all indicators red.
  2. False. All substances are classified as acidic, basic or neutral.
  3. False. As it is a neutral solution, the colour of the litmus paper will not change.
  4. True
  5. False. Phenolphthalein is an artificial indicator.
  6. True
  7. False. Lemon water is acidic.

Question 6. Consider the following statements:

(a) Both acids and bases change the colour of all indicators.

(b) If an indicator gives a colour change with an acid, it does not give a change with a base.

(c) If an indicator changes colour with a base, it does not change colour with an acid.

(d) The change of colour in an acid and a base depends on the type of indicator.

Which of these statements is correct?

(i) All four 

(ii) a and d 

(iii) b, c and d 

(iv) only d

Answer 6. (iv) Only d

Explanation : 

(a) Not all indicators cause acidic or basic substances to change colour. For example, the phenolphthalein indicator used in the neutralisation process is colourless in acid but changes to pink in bases.

(b) Indicators can give a colour change for both acid and base. For example, When a litmus solution is added to an acidic solution, it turns red, and when added to a basic solution, it turns blue.

(c) An indicator that changes colour when exposed to a base can or cannot change colour when exposed to acid.

For example, the turmeric indicator changes to red in the base but does not show any colour change in the acid.

(d) Hence, the change of colour in an acid and a base depends on the type of indicator and is the correct answer.

Question 7. Fill the blanks in the below-given sentences

(a) Turmeric and litmus are _________ acid-base indicators.

(b) Lemon juice and vinegar taste ___________ because they contain ___________.

(c) When an acidic solution is mixed with a basic solution, they _________ each other forming _________ and water.

(d) Phenolphthalein gives _________ colour with lime water.

Answer 7. 

(a) Natural

(b) Sour, acids

(c) Neutralise, salt

(d) Pink

Question 8. Explain two neutralisation reactions related to daily life Situations.

Answer 8. The two neutralisation reactions related to our daily life situation are,

  • Indigestion: Excessive hydrochloric acid in the stomach causes indigestion. To neutralise the effect of excessive acid and relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide.
  • Ant bite: When an ant bites, it injects formic acid into the skin. Rubbing the moist baking soda, which contains sodium hydrogen carbonate or calamine solution containing zinc carbonate, can neutralise the effect of the acid.

Question 9. Mark true or false for the below statements. Correct the false statements.

(a) Nitric acid turns red litmus blue.

(b) Sodium hydroxide turns blue litmus red.

(c) Sodium hydroxide and hydrochloric acid neutralise each other and

produce water and salt. 

(d) Indicator shows different colours in acidic and basic solutions. 

(e) Tooth decay is caused due to the presence of a base. 

Answer 9. 

(a) False. Nitric acid is acidic. Substances with an acidic nature will turn the blue litmus paper red.

(b) False. Sodium hydroxide is basic. Substances of a basic nature will turn the red litmus paper blue. If we use blue litmus paper, it will not change the colour.

(c) True.

(d) True.

(e) False. Tooth decay is caused due to the degradation of food particles that get stuck in the teeth, and the bacteria (Streptococcus) consume them to convert the glucose, fructose, and sucrose of the food items into lactic acid. The high level of lactic acid accumulated in the teeth leads to the fermentation of more sugars and creates plaque and cavities, which, when not taken care of for a long time, can cause tooth decay.

Note: The presence of a base substance neutralises the acid and protects it from tooth decay.

Question 10. Look at the given reaction.

Hydrochloric acid + Sodium hydroxide (base) → Sodium chloride (salt) + 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 10. Yes, we can get solid chloride from the solution by evaporation process.

The water evaporates and forms sodium chloride crystals by heating the sodium chloride solution.

Question 11. Match the substances in Column I with those in Column II.

                        Column I           Column II
  • Tartaric acid
(i) Soap
  • Calcium hydroxide
(ii) Curd
      (c)  Formic acid (iii) Unripe mangoes
      (d) Sodium hydroxide (iv) Ant’s sting
      (e) Lactic acid (v) Lime water

Answer 11. The matched substances are given below,

                        Column I           Column II
  1. Tartaric acid
(i) Unripe mangoes
  1. Calcium hydroxide
(ii) Lime water
      (c)  Formic acid (iii) Ant’s sting
      (d) Sodium hydroxide (iv) Soap
      (e) Lactic acid (v) Curd

Question 12. Frame a sentence using the following words – baking soda, ant bite, moist, effect, neutralised, rubbing.

Answer 12. The effect of an ant bite can be neutralised by rubbing the moist baking soda.

Question 13. Ammonia can be found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Answer 13. Ammonia is basic. Hence, it turns red litmus blue.

Ammonia is classified as a weak base, as its molecules don’t completely break down into ions in water.

Question 14. 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) Slaked lime

(c) Quick lime

(d) Calamine solution

Answer 14. (a) Organic matter

Explanation: When the soil is too basic, the fertility of the soil is reduced, and plants do not grow well. We must add organic matter to replenish soil fertility, as it releases acids that react and neutralise the excess base in the soil.

Question 15. Which of the following is an extract of ‘Litmus,’ a natural dye?

(a) China rose (Gudhal)

(b) Beetroot

(c) Lichen

(d) Blueberries (Jamun)

Answer 15. (c) Lichen

Explanation: Litmus is extracted from lichen algae living among the strands of multiple fungi species. Litmus paper is commonly used as an acid-base indicator.

Question 16. What is acid rain?

Answer 16.Due to excess air pollutants such as carbon dioxide, sulphur dioxide and nitrogen dioxide released into the air, the raindrops dissolve all of these pollutants to form carbonic acid, sulphuric acid and nitric acid, Acid rain can cause damage to plants, and animals, buildings, and historical monuments.

Question 17. What are salts? Explain with the help of an example.

Answer 17. Salt and water are produced in the neutralisation reaction between acid and base. Salt may be acidic, basic or neutral. For Example

Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)

From the above reaction, sodium chloride is produced in the form of salt.

Benefits of Solving Important Questions Class 7 Science Chapter 5

Important Questions Class 7 Science Chapter 5 consists of all types of questions, including MCQs, short and medium-format questions and answers, CBSE extra questions, and long-answer questions with step-by-step solutions to make students well-versed with various questions appearing in the CBSE examination.

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  • The questions and answers to all the Important Questions in Class 7 Science Chapter 5 are carefully chosen by our experienced Science teachers as per the CBSE syllabus and NCERT guidelines and by referring to various trusted sources, including NCERT textbooks, NCERT exemplar books, past years’ question papers, and other sources.
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Q.1 Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and the third is a sugar solution. How will you identify them when you are only provided with turmeric powder?


Turmeric solution turns red in contact with bases and is not affected by acids and neutral substances. So, we put turmeric indicator in some portions of all the three liquids labeled as A, B, and C respectively. ‘B’ would turn red, indicating that it is a base.

Then, one of the liquids ( A or C) is added to the solution of sodium hydroxide and turmeric powder. If the solution turns yellow, the added liquid is hydrochloric acid because acid neutralises the base. Otherwise, if no change is observed, the added liquid is the sugar solution.

Q.2 How does hydrochloric acid help in the digestion of food?



HCl plays an important role in the digestion of food in our stomach. HCl makes the medium acidic, so that gastric enzymes may act on the food. It also kills the disease causing germs that come along with the intake of food.

Q.3 Select the correct match.

(a). a – p, b – q, c – s, d – r

(b). a – q, b – s, c – p, d – r

(c). a – r, b – s, c – p, d – q

(d). a – r, b – p, c – s, d – q



(d). a – r, b – p, c – s, d – q

Q.4 The acidic soil is not good for healthy growth of plants. This type of soil is neutralized by adding

(a). ammonium chloride (NH4Cl) to the soil.

(b). calcium oxide (CaO) to the soil.

(c). sodium chloride (NaCl) to the soil.

(d). organic matter to the soil.



(b). calcium oxide (CaO) to the soil.

This soil is neutralized by adding calcium oxide (CaO), which is basic in nature.

Q.5 An example of synthetic indicator is

(a). litmus

(b). phenolphthalein

(c). turmeric

(d). china rose extract



(b). phenolphthalein

Phenolphthalein is a synthetic indicator, which is colourless and changes its colour to pink in basic medium.

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