NCERT Solutions Class 7 Science Chapter 4 - Acids, Bases and Salts

Acids, Bases, and Salts is the fourth chapter of Class 7 Science, providing a comprehensive understanding of these important chemical substances. This chapter covers key concepts such as acids and bases, the different types of natural indicators around us, and the process of neutralisation. Additionally, it explores the significance of neutralisation in everyday life, helping students understand its practical applications. For students seeking a deeper grasp of the subject, the NCERT Solutions Acids, Bases and Salts Class 7 offers detailed explanations, making it easier to solve textbook problems and enhance their learning experience.

1.0Download Class 7 Science Chapter 4 NCERT Solutions PDF Online

This article offers Acids, Bases and Salts class 7 solutions as per NCERT. Practicing these solutions will help students develop a strong foundation in Chemistry and gain clarity on how to approach related problems effectively, ultimately aiding in securing good scores in board exams. For a detailed understanding, students can download the NCERT Solutions for Class 7 Science Chapter 4 PDF solution below, curated by ALLEN’s experts.

2.0Class 7 Science Chapter 4 Acids, Bases and Salts Overview

Before getting into the details of NCERT Solutions For Class 7 Science Chapter 4 Acids, Bases and Salts. Let's take a brief look at the topics and subtopics covered in this chapter of the NCERT Class 7 Science book.

Topics covered in this chapter

• Acids and Bases
• Natural Indicators Around Us
• Neutralization
• Neutralization in Everyday Life

3.0NCERT Questions with Solutions for Class 7 Science Chapter 4 - Detailed Solutions

• State differences between acids and bases. Ans.

• Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature? Ans. Ammonia is basic in nature as it turns the colour of red litmus paper to blue.
• Name the source from which litmus solution is obtained. What is the use of this solution? Ans. Litmus solution is obtained from lichens. A natural dye extracted from lichens is dissolved in distilled water to obtain litmus solution. It is used as an indicator to distinguish between acids and bases.

• Is the distilled water acidic/basic/neutral? How would you verify it? Ans. Distilled water is neutral in nature. The same can be verified by using red and blue litmus papers. Neither will show a colour change with distilled water. This proves that distilled water is neutral.
• Describe the process of neutralisation with the help of an example. Ans. The reaction between an acid and a base is known as neutralisation reaction. In this reaction, both acid and base cancel each other's effect. Neutralisation reaction results in the formation of salt and water. During this reaction, energy in the form of heat is evolved. Acid + Base $⟶$ Salt + Water + Heat For example, when sodium hydroxide $(\mathrm{NaOH})$ is added to hydrochloric acid $(\mathrm{HCl})$, sodium chloride $(\mathrm{NaCl})$ and water $\left({\mathrm{H}}_2\mathrm{O}\right)$ are obtained. $\mathrm{NaOH}+\mathrm{HCl}⟶\mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}+$ Heat
• Mark ' T ' if the statement is true and ' F ' if it is false: (i) Nitric acid turns red litmus blue. (T/F) (ii) Sodium hydroxide turns blue litmus red. (T/F) (iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. (T/F) (iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F) (v) Tooth decay is caused by the presence of a base. (T/F) Ans. (i) (F) (ii) (F) (iii) (T) (iv) (T) (v) (F)
• Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom? Ans. Since the drinks are edible, Dorji can take the decision by tasting the drinks. Acidic drinks will be sour in taste whereas basic drinks will be bitter in taste and neutral drinks will have no taste. He can also use litmus paper to identify acidic, basic and neutral drink. 1.If Dorji has litmus indicator (solution or paper), then he can take its help. He should put one drop of each drink on blue litmus paper. If the colour of the litmus paper changes to red, then it is an acidic drink. 2.Out of the remaining drinks, some are basic and some are neutral. Again, he should put one drop of the remaining drinks on red litmus paper. If the colour changes to blue, then it is basic and the others are neutral. In this way, he can serve all the three customers their respective drinks.
• Explain why: (a) An antacid tablet is taken when you suffer from acidity. (b) Calamine solution is applied on the skin when an ant bites. (c) Factory waste is neutralised before disposing into the water bodies. Ans. (a) This is because during acidity, an excess of acid is produced in the stomach. An antacid contains a base, such as milk of magnesia. This base reacts with excess of acid and neutralize its effect, thus giving us relief. (b) When an ant bites, it injects formic acid into the skin. Calamine solution contains zinc carbonate which is basic in nature. Therefore, it is applied on the skin to neutralize the effect of formic acid. (c) Factory wastes contain acids. Therefore, these wastes, when thrown directly to water bodies, harm aquatic lives. Hence, these wastes are neutralized with basic chemicals before disposing to water bodies.
• 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? You have only turmeric indicator. Ans. 1. We will put a drop each of hydrochloric acid, sodium hydroxide, and sugar solution on the turmeric indicator. The liquid which changes the colour of turmeric indicator to red is basic in nature, that is, sodium hydroxide. 2.Now, we will put a drop of sodium hydroxide on a drop of each of the other two liquids separately. After that, we will put the drops of these mixtures on turmeric indicator. The drop which will change the colour of the turmeric indicator to red contains sugar solution. This is because the mixture of basic and neutral solution is basic in nature. 3.On the other hand, the drop which will not change the colour of turmeric indicator contains hydrochloric acid. This is because hydrochloric acid reacts with sodium hydroxide to form a neutral solution.
• Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain. Ans. The above solution could be a base or a neutral solution because: 1.Bases turn red litmus to blue but do not react with blue litmus. 2.Neutral substance also does not react with litmus solution.
• Consider the following statements: (a) Both acids and bases change 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) Change of colour in an acid and a base depends on the type of indicator. Which of these statements are correct? (i) All four (ii) a and d (iii) b and c (iv) only d Ans. (iv) Only d is correct.

Exercise -01

Multiple choice questions

• The Latin word acere means (1) sweet (2) bitter (3) both (1) and (2) (4) sour
• Which of the following is acidic in nature? (1) Lime juice (2) Human blood (3) Lime water (4) Antacid
• Which of the following is a property of an acid? (1) Sour taste (2) Sweet taste (3) Bitter taste (4) Salty taste
• The acid produced naturally in our stomach is : (1) tartaric acid (2) citric acid (3) hydrochloric acid (4) sulphuric acid
• Lactic acid is found in (1) Curd (2) Soap (3) Apple (4) Lime
• Sodium hydroxide is found in (1) lemon (2) soap (3) table of salt (4) amla
• Which of these is not a base? (1) soap (2) lime water (3) curd (4) ammonia
• The substances which change their colour on coming in contact with other substance are called (1) acids (2) bases (3) indicators (4) none of these
• Litmus is made from which of these? (1) Algae (2) Fungi (3) Lichen (4) Bacteria
• Acid turns blue litmus to (1) green (2) red (3) yellow (4) black
• Which is the correct set of acid properties? (1) sour, corrosive, changes blue litmus to red (2) sour, corrosive, changes red litmus to blue (3) sweet, slippery, change red litmus to blue (4) sour, slippery, changes blue litmus to red
• What is the colour of turmeric solution in presence of base? (1) Yellow (2) Red (3) Blue (4) Green
• The substances which react with acids to form salt and water, as the only products, are known as (1) bases (2) acids (3) salts (4) all of these
• Which of these is formed after neutralization reaction? (1) Acid (2) Base (3) Salt (4) Alkali
• Which of the following is true for acids and bases? (1) acids and bases do not react with each other (2) acids and bases neutralize each other (3) acids and bases make stronger acids (4) acids and bases make stronger base
• Which of the following colour is given by phenolphthalein in base? (1) green (2) pink (3) yellow (4) black
• Hydrochloric acid produced in the stomach is very important for (1) digestion of food (2) producing acidity in the stomach (3) both (1) and (2) (4) none of these
• Antacids made of magnesium hydroxide and aluminium hydroxide, are used for (1) relieving acidity in the stomach (2) for preparing bleaching powder (3) both (1) and (2) (4) none of these
• Manure is added when the soil is too (1) acidic (2) basic (3)neutral (4) none of these
• The sharp pain caused by the sting of red ants, nettle leaves and bees are due to (1) acetic acid (2) tartaric acid (3) ascorbic acid (4) formic acid

True or False

• Latin word acere means sour.
• Vitamin-C is also known as ascorbic acid.
• Acids feel slippery to touch.
• Acids are bitter to taste and soapy to touch.
• Ammonia water is found in soap.
• Acid turns blue litmus red.
• Turmeric is not used as indicator.
• China rose turns the colour of acidic solution to dark pink.
• Indigestion remedies are called antacids.
• Neutralization can also be used in making soap.

Fill in the blanks

• The acid found in lemons is acid.
• The sting of contains formic acid.
• The bases have a taste and touch.
• is used in the manufacturing of soap.
• The chemical formula of slaked lime is _.
• Reaction between acids and bases is called reactions.
• When acids and base react, the products formed are and .
• Phenolphthalein turns in colour in a base.
• A farmer treats the soil of his field with lime when the soil has nature.
• An ant bite can be treated by applying a solution.

Crossword puzzle

Across

• Litmus is extracted from .
• A laboratory indicator turns pink in basic solution.
• China rose indicator turns acidic solutions into .
• Sour in taste.

Down

• In neutralisation reaction a new substance is formed. This is called _.
• Our stomach contains acid.
• Acids and bases are ___ in nature, irritating and harmful to skin.
• Feel soapy to touch.

Answer Key

Multiple choice questions

True or False

• True
• True
• False
• False
• False
• True
• False
• True
• True
• False

Fill in the blanks

• citric
• ants
• bitter, soapy
• sodium hydroxide
• $\mathrm{Ca}(\mathrm{OH}{)}_2$
• neutralization
• salt and water
• pink
• acidic
• calamine

Crossword puzzle

Exercise -02

Very short answer type questions

• Name the acid present in curd.
• Classify the following substances into acidic and basic substances Tomato juice, soap solution, toothpaste, lemon juice, vinegar
• What is the nature of soap solution?
• What is the nature of distilled water?
• Which of these is neutral - hydrochloric acid, sodium hydroxide, sodium chloride?
• What is acid rain?
• What is an indicator?
• Which is the most commonly used natural indicator?
• If a liquid turns blue litmus red, is it an acid, base or salt?
• What are antacids?

Short answer type questions

• Tom rubs a solution between fingers and feels soapy, what is the nature of that solution?
• Name one each of acidic, basic and neutral substances.
• What are indicators? Why do we use it? Give examples.
• What are indicators? Name any three indicators and state the colour change which takes place in (i) acids (ii) bases
• When red litmus paper is dipped in a solution; it remains red, what is the nature of the solution?
• Give reason turmeric stain turns red when soap solution is applied to it.
• You are given three unlabelled bottles A, B and C, containing colourless solutions, such that one of them is acid, the other basic and the third neutral. How will you distinguish between them by using blue litmus as an indicator?
• What is neutralisation reaction? Give one example.
• How acidic soil can be treated?
• Why should industrial waste be treated before disposing it into the rivers? Long answer type questions
• Why most of the fruits or vegetables taste sour? Name the acid that is used as an eye wash. Also write any two physical properties of bases.
• Can turmeric paper be used to differentiate between an acid and a neutral solution? Explain your answer.
• What do you mean by a neutralization reaction? How can a neutralization reaction be used to prepare common salt?
• What do you understand by the term neutralisation? Describe an activity in which neutralisation of hydrochloric acid takes place with sodium hydroxide, using phenolphthalein as an indicator.
• Explain why (a) Farmers add slaked lime to acidic soil. (b) Soap solution or baking soda paste is applied on the part of the body stung by a bee. (c) Antacids are used for relieving acidity in the stomach. (d) Baking soda is used for preservation of milk.

Exercise-01 Solutions

Multiple choice questions

• Option (4) The word acid come from latin word 'acidus' meaning sour in taste.
• Option (1) Lime juice is acidic in nature because it releases ${\mathrm{H}}^{+}$ions in aqueous solution. It is an organic acid.
• Option (1) Acidic substances have sour taste.
• Option (3) Hydrochloric acid is produced naturally in our stomach.
• Option (1) Lactic acid is found in curd.
• Option (2) Sodium hydroxide is found in soap.
• Option (3) Curd is an acidic substance.
• Option (3) Indicators are chemicals which indicates by the means of a sharp change in colour, the nature of the solution.
• Option (3) Litmus is obtained from a plant called lichen.
• Option (2) Acid turns blue litmus to red.
• Option (1) Acids are sour in taste, corrosive and they change blue litmus to red.
• Option (2) Bases turn turmeric indicator to reddish brown.
• Option (1) Bases react with acid to form salt and water.
• Option (3) Salt and water are the products of neutralisation reaction.
• Option (2) Acids and bases neutralise each other.
• Option (2) Bases give pink colour in presence of phenolphthalein indicator.
• Option (1) Hydrochloric acid is very important for digestion of food in our stomach.
• Option (1) Antacids are used to relieve acidity in our stomach because they are mild bases which can neutralise excess amount of acid present in stomach.
• Option (2) Manure is added when soil is too basic.
• Option (4) The sting of red nettle leaves and ants, bees inject formic acid in our body which cause sharp pain and irritation.

True or false

• True Latin word acere means sour.
• True Vitamin-C is also known as ascorbic acid.
• False Bases feel slippery to touch.
• False Bases are bitter in taste and soapy to touch.
• False Sodium hydroxide is found in soap.
• True Acid turns blue litmus paper to red.
• False Turmeric is used as indicator.
• True China rose turns the colour of acidic solution to dark pink.
• True Indigestion remedies are called antacids.
• False Neutralization cannot be used in making soap.

Exercise-02 Solutions

Very short answer type questions

• Lactic acid is present in curd.
• Tomato juice, lemon juice, vinegar Acidic. Soap solution, toothpaste - Basic.
• The nature of soap solution is basic.
• Distilled water is neutral in nature.
• Sodium chloride is the neutral substance.
• The rain containing excess of acids is called an acid rain. Rainwater contains dissolved carbon dioxide. Hence, it is slightly acidic.
• It is a chemical which indicates the nature of a solution by the means of a sharp change in colour.
• Litmus is the most commonly used natural indicator.
• If a liquid turns blue litmus red, it is an acid.
• Antacids are the chemical substances used as a medicine, contain weak bases like baking soda to provide the relief in the case of acidity in our stomach.

Short answer type questions

• The nature of the solution is basic. Basic substances feel soapy to touch.
• Acidic substance : HCl (Hydrogen chloride) Basic substance : NaOH (Sodium hydroxide) Neutral substance: NaCl (Sodium chloride)
• Indicators are those substances which indicates the nature of solution either it is acidic, basic or neutral by sharp change in colour. Ex. Litmus, turmeric, China rose, methyl orange, phenolphthalein.
• Indicators are those substances which indicates the nature of solution either it is acidic, basic or neutral by sharp change in colour.

• When red litmus paper is dipped in a solution; it remains red, then it may be either acidic or neutral.
• Because soap is basic in nature and turmeric gives red colour in presence of bases.
• Bottle $C\to$ No change $\to$ Neutral Bottle $\mathrm{A}\to$ Change blue to red $\to$ Acid Bottle B $\to$ Blue remains blue $\to$ Base
• When an acid reacts with a base to produce salt and water, the reaction is called neutralisation reaction. $\mathrm{HCl}+\mathrm{NaOH}\to \mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}$
• In order to convert acidic soil into neutral soil farmers spray it with calcium oxide (quick lime) or calcium hydroxide (slaked lime). These chemicals neutralise soil acids and hence soil becomes neutral.
• The wastes of many factories contain acids. If these wastes are directly discharged in a river or a lake, they kill the fish and other living organisms. Thus, to prevent such a situation, the wastes are treated with lime which neutralises acids.

Long answer type questions

• Most of the fruits or vegetables taste sour because they contain acids. Boric acid is used as an eye wash. Physical properties of bases. (i) Bases are bitter in taste. (ii) Bases feel soapy to touch.
• Turmeric (haldi) is commonly used as a spice in kitchen. It is yellow in colour and stains a white cloth yellow. If the yellow stain is rubbed with soap solution, the colour of the stain changes to brownish red. Why does this happen? The soap solution always contains a small amount of chemical called sodium hydroxide. It is the sodium hydroxide which changes the colour of turmeric stain from yellow to brownish red. Now, if we rub stain, it again changes to yellow colour. The lemon contains another substance called citric acid, which neutralises the effect of sodium hydroxide.
• When acidic and basic substances react with each other. Salt and water is formed. This is called neutralisation reaction. When we mix hydrochloric acid with sodium hydroxide, sodium chloride i.e. salt is formed. $\mathrm{HCl}+\mathrm{NaOH}\to \mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O}$ This is called neutralisation reaction and it can also be used to prepare common salt.
• The reaction between an acid and a base is known as neutralisation reaction. It results in the formation of salt & water. During this reaction energy in the form of heat is evolved. Acid + Base $\to$ Salt + Water + Heat. Activity: To show that acid react with alkalis and a neutralisation reaction take place. Pour about 20 ml of sodium hydroxide solution in the beaker. To this solution, add phenolphthalein solution you will notice that solution turns deep pink. Fill the dropper with dil. HCl allow the acid to fall in the beaker drop by drop. Go on stirring the beaker. Observation. You will notice that at some stage, by the addition of one drop of acid the solution suddenly becomes colourless, which shows that sodium hydroxide solution has been completely neutralised by acid.
• (a) Plants grow well only in the neutral soil however, sometimes a neutral soil gets acidic due to excessive use of artificial fertilisers. The soil also gets acidic, if the roots of harvested crop are allowed to decay in it. This in turn reduces the fertility of the soil. In order to convert acidic soil into neutral soil farmers spray it with calcium oxide (quick lime) or calcium hydroxide (slaked lime). These chemicals neutralise soil acids and hence soil becomes neutral. (b) The stings of ants and bees contain formic acid. when these insects sting, they inject formic acid in our body which causes painful irritation & swelling. To reduce the effect of formic acid, the area around the sting is rubbed with a soap or baking soda solution or calamine which contains zinc carbonate. These substances neutralise the effect of formic acid to some extent & hence, help in relieving pain. (c) Our stomach walls produce, gastric juice which contains hydrochloric acid. The gastric juice helps in the digestion of food. However, when we eat very spicy food or have worries or tension, the stomach wall produces a large amount of HCl which leads to acidity in stomach. One has a burning feeling in the stomach & sour taste in the mouth. This condition is commonly called" acidity of stomach or indigestion". If not controlled it can damage the walls of stomach & can cause stomach ulcers. This extra acid can be neutralised by taking an edible base like baking soda. Antacids are edible base like baking soda. They neutralise the excess amount of acid produced by stomach walls and decrease the amount of acid which help us in relieving pain. (d) Preserving milk for a short period: Milk is brought to the cities from the villages by the vendors. In hot climates the natural bacteria present in the milk produces a large amount of lactic acid. To prevent the ill effect of lactic acid the milk vendor adds a small amount of baking soda to the milk. This neutralises lactic acid and the milk does not curdle.

4.0Benefits of Studying this Chapter 

1. Clear Understanding of Concepts: NCERT solutions explain key concepts such as acids, bases, and salts in simple language, helping students grasp these essential topics more effectively.
2. Step-by-Step Solutions: The solutions provide detailed, step-by-step explanations for all textbook questions, ensuring students can understand the logic behind each answer.
3. Helps with Homework and Exams: These solutions serve as a reliable reference for homework and exam preparation, ensuring students can answer questions confidently.
4. Improves Problem-Solving Skills: By working through NCERT questions and solutions, students enhance their analytical and problem-solving abilities.
5. Boosts Confidence: Mastering the concepts and questions in this chapter gives students the confidence to tackle more advanced science topics in higher classes.

By studying these solutions, students can ensure a thorough preparation for their exams and gain a deeper understanding of basic chemistry concepts.