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Chapter 5

Acid, Bases, And Salts

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  • CBSE
  • Class 7
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  • Acid, Bases, And Salts

Topics Covered in this Chapter: Acids, Bases and Salts:

  1. Introduction

  2. Acids

  3. Bases

  4. Salts

  5. Natural Indicators

    1. Neutralisation in Everyday Life

    2. Frequently Asked Questions

    3. Conclusion

Introduction

Acids, bases and salts are present in our everyday life: table salt is a neutral salt, apples contain malic acid, soaps are made with bases. Acids, bases and salts exhibit their unique chemical and physical properties. Moreover, acids, bases and salts can be combined to create new chemicals.

Acids

The word ‘acid’ is derived from the Latin word ‘acere’ or ‘acidus,’ which means sour. Products containing acid usually have a strong sour taste. Acids present in food items are natural acids. Some food items, which have acid in their chemical composition are oranges, lemons, vinegar, curd etc. Lemon contains citric acid; vinegar contains acetic acid and so on. 

Acid is corrosive in nature. It turns blue litmus paper, a neutral testing paper, to red. There are different types of acids such as lactic acid, acetic acid, formic acid, oxalic acid, tartaric acid, ascorbic acid etc. 

Bases

Substances that contain bases are usually soapy to touch and taste bitter. Bases are also prevalent in everyday products such as ammonia, washing powder, soap, bleach, baking powder, toothpaste, paper glass etc. They are also present in various food items like bread, cake, pastries, cookies etc.

Bases turn red litmus paper to blue. There are different types of bases such as sodium hydroxide, lithium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide and rubidium hydroxide. Soluble bases are also known as alkalis. Alkaline solutions can conduct electricity.

Salts

Salts are a product of the neutralisation process. Salt does not have a definite chemical structure and contains acids and bases. Salt may contain either a strong acid and a weak base or a weak acid and a strong base. Similar to acids and bases, salts are also prevalent in everyday life. Some food items that contain salts are common salts, also known as sodium chloride. Common salt is present in all food items, especially the cooked ones for taste. Salts also help in fermentation and food preservation and are present in other essential substances like pesticides, medicines and photo paper.

It is essential to use indicators to identify whether an item is an acid or a base. 

Natural indicators that determine whether an item is an acid or a base are listed below:

  1. Litmus: One of the easiest and best ways of identifying acid and base is by using litmus. Litmus paper is a filter paper produced with a natural dye obtained from lichens. It is also available as a solution. Litmus paper comes in two colours, red and blue. The red paper turns blue when it comes in contact with a base, and the blue paper turns red when it comes in contact with an acid. 

  2. Turmeric: Turmeric is acidic. When it is mixed with any basic solution, it turns red from its natural yellow colour. A tablespoon of turmeric is enough to determine whether any solution or mixture is acidic or basic. If the item is acidic, the turmeric will not change its colour. A paper drenched in turmeric paste and a drop of soap is enough to create a turmeric indicator. Turmeric as an indicator works on vinegar, baking soda and citruses. In a neutral solution, the colour of turmeric remains the same as it is neither acidic nor basic. 

  3. China Rose: China rose is a natural indicator. The red colour that comes out of China rose dipped in water for thirty minutes is also a good indicator. The red colour solution changes colour when it comes in contact with an acid or a base. It turns an acidic solution into a dark pink colour. It also transforms a basic solution into green colour. However, China rose does not change colour when it comes in contact with neutral solutions. 

The natural indicators of acids and bases are available quite easily and are prevalent in our everyday life.

Neutralisation reactions occur in our everyday lives. The following are a few examples:

  1. Ant Bite: Ant bite is a very common thing. But the sting pains a lot as ants inject acid when they bite. Applying a basic solution like baking soda helps in easing the pain because the basic solution reacts with the acid quickly. This reaction neutralises the effect of the acid and reduces the pain. 

  2. Digestive Problems: Digestive Problems are a common health problem. When people eat a lot, they tend to face acidity because the amount of acid in the digestive system increases. The intake of an antacid made of milk of magnesia, which is a base, eases the pain. The antacid reacts with the acid and reduces the effect of the acid in the stomach. 

  3. Factory Waste Treatment: Factory waste is hazardous and acidic. If the factory workers do not treat it properly it could destroy all aquatic life. Before dispensing the factory waste in the sea, factory workers should treat it with a base to reduce the acidic effect.

  4. Soil Treatment: Fertilisers are acidic. The excessive use of fertilisers is harmful to the soil. With the use of fertilisers, the soil becomes acidic. Farmers use bases like quick lime and calcium hydroxide to neutralise the effect of acid in the soil.

1. Write the differences between Acids and Bases.

The major differences between acids and bases are:

  • Acids are sour whereas bases are bitter to taste. 
  • In the litmus test, acids turn blue litmus paper into red whereas bases turn red litmus paper into blue. 
  • In the turmeric test, acid does not change the colour of the turmeric paper whereas bases change the colour of the turmeric paper from yellow to red. 
  • In the China rose test, acids change the colour of the China rose solution from red to dark pink whereas bases turn the China rose solution into a green colour. 

2. Define natural indicators. Name the natural indicators of everyday life. 

Natural indicators are natural substances that are found in our everyday life and are used to determine acids and bases. They also test the pH level of the solutions since they have neutral pH. Indicators are important to classify substances as acids or bases. Some of the natural indicators include litmus, turmeric, China rose etc. These indicators can be efficiently used to indicate whether a particular substance is an acid or a base. However, they do not change colour when they come in contact with a neutral solution. 

3. Explain neutralisation reaction.

Neutralisation is the process of balancing acids and bases. In our daily life, this may include neutralising ant bites, reducing digestive problems, treating hazardous factory waste, and increasing the pH level of soil. Neutralisation is essential because acids and bases should be present in equal amounts. Otherwise, they may produce adverse effects. An example of this may be acidity in the human body. When there is a lot of food consumption the stomach excretes excessive acid, which may cause indigestion, acid reflux and several other problems in the body. To combat this problem, doctors generally prescribe antacids containing the milk of magnesia. Milk of magnesia is a base that neutralises the acid in the body and provides relief. 

4. What are salts? State the uses of salts.

Salts are products of neutralisation. Salts have no specific structure and consist of both acids and bases. Salts are either composed of a weak acid and a strong base or a strong acid and a weak base. Salt is a necessary requirement of our everyday life. Common salt or sodium chloride is an essential ingredient in cooking. Salts are also used in the fermentation of pickles, food preservation, medicines, chemical fertilisers etc. It is also present in photographic paper, films and other items.

Acids, Bases and Salts form a substantial part of the science curriculum. Therefore, students must learn the chapter carefully. They must also solve the question papers related to this chapter. MSVGo is an e-platform that provides detailed study materials of the CBSE curriculum. They also have an app that offers excellent video lectures related to the CBSE curriculum. So, if you are looking for a platform to guide you while studying this chapter, then MSVGo is the right platform for you. Join MSVGo to access exclusive content related to the Acids, Bases and Salts chapter now!

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