NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases, and Salts

Are you looking for NCERT Solutions for your preparation? Look no further. Extramarks offers NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases, and Salts that students can utilise for their preparation. These solutions include detailed step-by-step answers to the questions of this chapter that students will find very useful. These solutions can be accessed from the links provided below.

NCERT Solutions for Class 7 Science Chapter 5 

Access NCERT Solutions for Class 7 Science Chapter 5 – Acids, Bases, and Salts

Chapter 5 of the Class 7 Science NCERT textbook introduces students to the concepts of Acids, Bases, and Salts. It talks about the properties of acids and bases, how to identify acids and bases using indicators, the different types of indicators used, and much more. Since Acids, Bases and Salts is one of the important chapters that students will further learn in higher grades, they should really try to build a strong base with this chapter. A thorough reading of the chapter along with the NCERT Solutions for Class 7 Science Chapter 5 provided by Extramarks will be sufficient for students to build a strong understanding of this important topic.

Chapter 5 – Acids, Bases, and Salts

Acids, Bases, and Salts are a vital segment of Chemistry in Science. Without these three substances, Chemistry is not complete. Chapter 7 introduces students to these concepts by giving a lot of practical examples that students will be able to relate to. The different topics covered in the chapter have been discussed below.

Acids and Bases

I am sure that you must have had a glass of lemon juice to beat this scorching summer. How does it taste? It is sour, isn’t it? That is because it contains acid. An acid is a substance that tastes sour, and it also turns the blue litmus into red and helps in neutralising bases. Can you remember some more food items that taste sour? Some common examples are; Citrus fruits, apples, plums, curd, pineapple and many more. These items are acidic in their chemical aspects. The food items that taste bitter and give a soapy feeling when touched are basic. But not all acidic and basic substances can be eaten. For this reason, we use the indicators for testing the acidic and basic nature of the substances. Some natural indicators are turmeric, China rose petals, litmus, etc.

Natural Indicators Around Us

Indicators help us find out which substance is acidic and which is basic. An indicator is any substance that changes colour when added to or touched with acidic or alkaline substances. There are several naturally occurring indicators for this purpose.

Litmus: A Natural Dye

The most commonly used natural indicator is litmus which is extracted from Lichens. A litmus indicator turns red when added to an acidic substance, and it turns blue when in contact with a basic substance. A litmus turns purple when added to neutral substances. You can get litmus in both solution form and stripes of paper. In this chapter, two natural indicators are explained. They are china roses and turmeric. 

In this chapter, various scientific experiments have been used to explain these concepts. Teachers might explain these concepts through practical experiments in the chemistry lab of your school.

Neutralisation

Chemistry and its experiments have always been interesting. For that reason, students might have curiosity about what happens when an acid is mixed with a base? In this section, we will discuss that. The term neutralisation refers to a chemical reaction in which an acidic substance is mixed with a basic substance quantitatively. In simple language, it is the reaction between an acid and a base. The process of neutralisation produces salt and water. Besides, heat is also released. In the latter section, we will also learn about phenolphthalein, an indicator, and its uses.

Neutralisation in Everyday Life

We might not realise it, but neutralisation takes place every day in our lives, and this is what we will learn about in this unit. Some of the regularly occurring neutralisation processes include:

  • Indigestion
  • Ant bite
  • Soil Treatment
  • Factory waste

Have you ever wondered why we take an antacid tablet when we suffer from gastric problems or acidity? Well, it is because antacid tablets are bases or basic in nature. So when it reacts with the excess acid present in our stomach, the process of neutralisation gets triggered. Thus, it relieves us from the pain. 

Salts get produced when an acid and a base neutralise each other. Salt can be either acidic, basic, or natural. 

Exercise Solutions: 11 Questions (2 short questions and 9 Long questions)

Class 7 Science Chapter 5 Acid, Bases and Salts contain 11 questions, out of which 9 are long questions and 2 are short questions.

Key Features of NCERT Solutions for Class 7 Science Chapter 5

Some of the key features of NCERT Solutions for Class 7 Science Chapter 5 are listed below.

  • The solutions can be accessed by students at any time by clicking the links provided above.
  • The solutions include detailed explanations wherever required so that students can comprehend them easily.
  • Subject matter experts prepare these solutions giving utmost attention to quality and accuracy so that students can rely on them for their preparation.

Q.1 State differences between acids and bases.

Acids

Bases
Acids are sour in taste. Bases are bitter in taste
Acids are non-soapy to touch. Bases are soapy to touch.
Acids turn blue litmus red. Bases do not change colour of blue litmus.
They do not change colour of red litmus. They turn red litmus blue.
Acids do not change the colour of turmeric indicator. Bases turn the colour of turmeric indicator to red.
Acids give magenta colour with china rose indicator. Bases give green colour with china rose indicator.
Examples of acids are citric acid, lactic acid, tartaric acid, etc. Examples of bases are sodium hydroxide, magnesium hydroxide, calcium hydroxide, etc.

Q.2 Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Ammonia is basic in nature as it turns red litmus blue. Bases turn red litmus blue.

Q.3 Name the source from which litmus solution is obtained. What is the use of this solution?

Litmus is obtained from Lichens.
Uses of Litmus solution

1. Litmus solution is used as an indicator. It is used to find the nature (acidic/basic/neutral) of the solution.
2. Acid solution turns blue litmus solution red.
3. Basic solution turns red litmus solution blue.

Q.4 Is the distilled water acidic/basic/neutral? How would you verify it?

Distilled water is neutral in nature. The same can be tested by using red and blue litmus paper. Acidic solution turns blue litmus paper red while basic solution turns red litmus paper blue. Distilled water neither turns blue litmus paper red nor red litmus paper blue. Therefore, distilled water is neutral.

Q.5 Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue.
(ii) Sodium hydroxide turns blue litmus red.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.
(v) Tooth decay is caused by the presence of a base.

(i) Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. (F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T)
(v) Tooth decay is caused by the presence of a base. (F)

Q.6 Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drink 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?

Since, soft drinks are edible; Dorji can decide acidic, basic and neutral soft drinks by tasting them. Acidic soft drink will be sour in taste whereas basic soft drink will be bitter in taste. Neutral soft drink will has neither sour taste nor bitter.

Acidic, basic and neutral soft drinks can also be decided by using blue and red litmus paper.

Dorji can pour a few drops of one soft drink on red and blue litmus paper. If red litmus turns blue, then it will be a basic soft drink and if blue litmus changes to red, then it will be an acidic soft drink. If colour of both the litmus papers remains same, then it will be a neutral drink.

The same process can be repeated with the other soft drinks also.

Q.7 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 it into the water bodies.

(a) Hydrochloric acid present in our stomach helps in the digestion of food. But excess of it causes acidity. To relieve from acidity, antacid tablets are taken as it contains base such as magnesium hydroxide that neutralises the acid present in the stomach.

(b) Formic acid is present in ant’s sting. When an ant bites, it injects the solution of formic acid into skin. The effect of sting can be neutralised by rubbing calamine solution on the stung area. Calamine solution being basic in nature neutralises the formic acid.

(c) The factory wastes contain acids. If such water is released into a water body, it can harm aquatic animals like fishes. Factory wastes should be treated with calcium hydroxide to neutralise acid before it is disposed off in water.

Q.8 Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Put a drop each of hydrochloric acid, sodium hydroxide and sugar solution on the turmeric indicator. The solution which changes the colour of turmeric indicator to red will be basic that is sodium hydroxide.

Now add a few drops of sodium hydroxide solution in remaining two solutions i.e. both in hydrochloric acid and sugar solution. After that, put some drops of these mixtures on turmeric indicator separately.

Drop that changes the colour of turmeric indicator will be neutral in nature i.e. sugar solution. Mixture of basic solution and neutral solution will be basic in nature and change the colour of turmeric indicator to red.

Drop that does not change the colour of turmeric indicator will be acidic in nature i.e. hydrochloric acid. This is because hydrochloric acid being acidic in nature neutralises the sodium hydroxide solution.

Q.9 Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

The nature of the solution will be either basic or neutral. This is because both basic solution and neutral solution do not change the colour of blue litmus paper.

Q.10 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 change colour 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 the indicator.

Which of these statements are correct?
(i) All four
(ii) a and d
(iii) b and c
(iv) only d

The correct option is (iv) only d.

Q.11 Describe the process of neutralisation with the help of an example.

The reaction between the acid and the base is known as neutralisation reaction. In the neutralisation reaction, salt and water are produced with the evolution of heat.
Acid + Base → Salt + Water + Heat

Example:
Hydrochloric acid (acid) reacts with sodium hydroxide (base) to form sodium chloride (salt) and water. Heat is evolved in this process.

Hydrochloric Acid(Acid)+Sodium Hydroxide(Base)→Sodium Chloride(Salt)+Water+Heat

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FAQs (Frequently Asked Questions)

Here are some important properties of base:

  • A base is a substance which tastes bitter. 
  • It gives a soapy feeling in a liquid solution. .
  • A base turns the red litmus paper into blue. 
  • It neutralises acids. 
  • It also promotes chemical reactions. 
  •  An example of one of the common bases is Sodium Hydroxide (NaOH).

Chapter 5 of Class 7 Science discusses three crucial elements of Chemistry- Acids, Bases, and Salts. In this chapter, the students will get a brief explanation of the various indicators that are used to test acids and bases. It also covers important concepts such as neutralisation.