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Chapter 5 – Acid, Bases, And Salts

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Many of the food items and things we use in our daily life have acids, bases, and salts in different forms. But how do we identify them? Our sense of taste is the first aid that comes to help.

Acid has a sour taste. The word acid comes from the Latin word acere, which means sour. Let’s see the acids contained in the food items:

 

Food ItemsType of Acid
VinegarAcetic Acid
Lemons, oranges, tomatoes, grapes, berries, pineapples, apples, bananas, pomegranatesCitric acid/ Malic acid/ Tartaric acid
Green leafy vegetables, beetsOxalic acid
CurdLactic acid

Bases have a bitter taste. They feel slippery to touch because they are soapy. Examples of bases we commonly use are:

 

ItemsTypes of bases
Paper, glass, detergent, toothpasteSodium carbonate
Baking Soda, Fire extinguisher,

Toothpaste

Sodium bicarbonate
PaperCalcium hydroxide
Limestone, Blackboard chalkCalcium carbonate
Sanitiser, disinfectantCalcium hydro chlorite

We have learned how acids and bases taste. But it may not be safe to taste everything. Therefore, we use a substance called Indicator to identify them.

Some of the most common natural indicators around us are Litmus, Turmeric, and China Rose petals, etc.

  1. Litmus is a dye extracted from a type of plant called ‘lichen.’ It has a mauve (purple) colour in distilled water.

    • Litmus turns red in an acidic solution, and blue in basic solutions.
    • There are two types of litmus paper – red litmus paper and blue litmus paper.
    • Blue litmus paper turns red when dipped in an acidic solution.
    • Red litmus paper turns blue when dipped in a basic solution.
  2. Turmeric (Haldi) is also a natural indicator. Turmeric does not change its yellow colour with acid but turns red when dipped in basic solution.
  3. China Rose is another natural indicator. Drops of China Rose water change the colour of an acidic solution to dark pink (Magenta) and turn a basic solution to green.

Let us understand the concept from examples of neutralisation in everyday life.

  • Acidity

We often experience a burning sensation in the stomach after eating very spicy food. This is due to the formation of excessive acid in our digestive system. Antacid, which has Milk of Magnesia consisting of Magnesium Hydroxide- a base, helps reduce this discomfort as it neutralises the excess acid.

  • Ant Bite

When an ant bites, it injects formic acid into the skin, causing pain. Rubbing with a basic substance such as baking soda (sodium hydrogen carbonate) or calamine solution (containing zinc carbonate) helps reduce the pain.

  • Soil Treatment

Excessive use of chemical fertilisers makes the soil acidic, which is harmful to the growth of plants. To neutralise the effect of excess fertilisers, bases like quicklime (calcium oxide) or slaked lime (calcium hydroxide) are mixed in the soil.

  • Factory Waste Treatment

Factory wastes are generally acidic. Therefore, basic substances are mixed with the wastes before releasing them into rivers to save aquatic lives.

From the examples cited above, we can observe that the process of neutralisation helps reduce the harmful effect of excess acid or base. The process involves a chemical reaction accompanied by the evolution of heat. We can represent it as:

    \begin{align*} \ce{Acid + Base &-> Salt + Water (Evolution of Heat)} \end{align*}

An example of the neutralisation reaction is:

\underset{\text{[Acid]}}{\ce{Hydrochloric acid (HCl) + }} \underset{\text{[Base]}} {\ce{Sodium Hydroxide (NaOH) = }} \underset{\text{[Salt]}} {\ce{Sodium chloride (NaCl) + }} Water (H2O)+ Heat

As we have seen above, salt is a substance produced during a neutralisation reaction. The chemical nature of salt can be acidic, basic, or neutral. To find out the nature of the salt, we use a synthetic indicator called Phenolphthalein. It is a pink coloured chemical dye. It turns colourless in acidic solutions and retains its pink colour in basic solutions.

Salt can be made of either a weak acid and strong base, strong acid and weak base, or a weak acid and weak base. Accordingly, it can be basic, acidic, or neutral.

Examples of salt in daily life and its uses:

    1. Common salt (Sodium chloride) in food.
    2. Food preservation, fermentation (as in pickles), baking, etc.
    3. Chemical fertilisers contain nitrogen, phosphorus, and potassium derived from salts such as ammonium chloride, ammonium nitrate, and ammonium phosphate.
    4. Pesticides – examples: copper sulfate, iron sulfate, etc.
    5. Medicines – widely used in iron pills, laxatives, antacids, disinfectants, etc.
    6. Industry – bleaching agent, photographic paper, films, etc.

We use acids, bases, and salts every day. You can conduct these simple experiments to determine if a food product or daily use product is made of an acid or base or salt. (Do remember to be careful and not taste some of the products directly.)

  1. What is the difference between acids, bases, and salts?
    An acid tastes sour and turns litmus paper to red. A base tastes bitter and turns litmus paper into blue, whereas a salt can be acidic, basic, or neutral.
  2. What are acid, base, and salt? Elaborate with examples.
    Acid is a sour-tasting substance found in our food, fruits, and vegetables, and various chemicals. Examples of acid are Acetic Acid in vinegar, Citric Acid in lemon and oranges, and Oxalic acid in green leafy vegetables.Bases are bitter-tasting compounds found in many materials we use in daily life. Examples include sodium bicarbonate in Baking Soda, sodium carbonate in detergents, calcium hydroxide in paper.Salt is a substance produced by the reaction of an acid with a base. Examples include sodium chloride in common or table salt used in food, sodium carbonate in washing soda, ammonium chloride, ammonium nitrate, potassium chloride in fertilisers.
  3. What are the characteristics of acids, bases, and salts?
    • Acid tastes sour. It turns blue litmus paper red. 
    • Bases taste bitter and turn red litmus paper blue. 
    • Salt is a crystalline substance that tastes salty. Its colour ranges from colourless to white.
  4. Is salt basic or acidic?
    A salt can be either a weak acid and strong base, strong acid and base, or a weak acid and weak acid and weak base. Accordingly, it can be basic, acidic, or neutral.

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High School Physics

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High School Chemistry

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  • Alcohols, Phenols and Ethers
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Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
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