You have landed on the right page to get an Introduction to Acids and Bases. You consume a wide variety of foods daily. Curd, lemon juice, honey, sugar, and other similar foods could be used. Do all of these foods have the same flavour? Can you think of a cause for the flavour difference? What do they usually consist of?

Almost everything you use every day, whether food or soap, is an acid or a base. Neutral substances, on the other hand, are chemicals that are neither acidic nor basic in nature. Let’s take a closer look at acids and bases in this article.

Acids

Because acids are present in lemon juice, orange juice, and vinegar, they have a sour flavour. Such compounds have an acidic chemical composition. The word ‘acid’ comes from the Latin word acere, which means sour. The fruits we’ve identified are some of the most frequent acids found in nature. Some acids are extremely potent and dangerous to work with. One of them is nitric acid. It has the potential to produce severe burns.

Types of Acids

Acids are classified into two types, and they are:

1. Organic Acids
2. Mineral Acids or Inorganic Acids

Organic Acids

Organic acids are acids that exist naturally. They can be found in many different kinds of plants and animals. Acetic acid, formic acid, citric acid, and lactic acid are some of the most important organic acids found in nature.

1. Acetic acid is found in vinegar. It is used as a preservative in foods.
2. The sting of an ant contains formic acid. The formic acid injected into our skin during an ant’s sting causes the acute discomfort we experience.
3. Citrus fruits, such as lemons and oranges, contain citric acid.
4. Lactic acid is present in curd and sour milk.

Organic acids (also known as naturally occurring acids) are a type of acid that is relatively weak. Eating or drinking things containing naturally occurring acids is not dangerous. For example, we can eat oranges or drink orange juice which contains natural acids. Similarly, we can consume lemon juice because it contains an organic acid (or natural acid) that does not harm us.

Mineral acids are acids made from minerals found on the surface of the earth. Mineral acids are acids that have been synthesised by humans. Because they are utilised in science laboratories, mineral acids are sometimes known as laboratory acids. The three most common mineral acids are:

1. Hydrochloric acid,
2. Sulphuric acid, and
3. Nitric acid.

We also use mineral acids in our daily life. Hydrochloric acid, for example, is used to clean kitchen sinks and bathroom sanitaryware (like washbasin and toilet seat). Storage batteries for vehicles, buses, lorries, and inverters are made with sulphuric acid. Goldsmiths use nitric acid for cleaning gold and silver ornaments.

Mineral Acids

What are Concentrated and Dilute Acids?

Concentrated Acids

Concentrated acids are those that have the greatest quantity of acid dissolved in the least amount of water. Commercially available acids are usually concentrated acids. Concentrated acids such as hydrochloric acid and sulphuric acid are available.

Dilute Acids

Dilute acids have a relatively small amount of acid dissolved in a big amount of water. In comparison to a concentrated solution, a dilute solution contains less solute.

Strong Acids and Weak Acids

Strong acids and weak acids are the two types of acids.

Acids that undergo ionisation to a large extent in an aqueous solution are called strong acids. For example, hydrochloric acid \(\left( {{\rm{HCl}}} \right)\), nitric acid \(\left( {{\rm{HN}}{{\rm{O}}_{\rm{3}}}} \right)\) and sulphuric acid \(\left( {{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}} \right)\).

Bases that undergo ionization to a small extent only are called weak acids. For example, carbonic acid \(\left( {{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}}} \right)\) and acetic acid \(\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}} \right)\).

The mineral acids are strong. Carbonic acid is the only mineral acid that is a weak acid. Drinking strong acids is quite harmful. Drinking even weak solutions of strong acids is exceedingly dangerous. Organic acids are a type of acid that isn’t very strong. Weak acid solutions in the dilute form are quite safe to consume. Organic acids like acetic acid, citric acid, and tartaric acid are employed as food components since they are weak.

Acetic acid is found in many foods, such as pickles and tomato ketchup, in the form of vinegar. Vinegar helps to keep fruits and vegetables fresh. The baking powder used in making cakes and biscuits contains tartaric acid. Though carbonic acid is not an organic acid, it is a weak acid. Carbonic acid is used in fizzy soft drinks and soda water. It gives them a pleasant taste.

Properties of Acids

All acids show some properties, which are as follows:

1. Acids are sour in taste.
2. Acids change blue litmus paper red.
3. Acids are corrosive in nature. They can spoil cloth, paper and even metals. That is why they are stored in glass bottles.
4. They can cause severe burn injuries on the skin.
5. Acids are good conductors of electricity in solution form.
6. Acids dissolve in water, form a dilute solution and produce heat. So, while making a dilute solution of an acid, always add acid to water slowly and never pour water on acid.
7. All acids except nitric acid react with metals such as zinc, magnesium, iron, etc., to form salts and release hydrogen gas.
   \({\rm{Zn + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {\rm{ZnS}}{{\rm{O}}_{\rm{4}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}\)
8. Acids react with carbonates such as calcium carbonate or sodium carbonate to form salts and carbon dioxide.
   \({\rm{CaC}}{{\rm{O}}_{\rm{3}}}{\rm{ + 2HCl}} \to {\rm{CaC}}{{\rm{l}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O + C}}{{\rm{O}}_{\rm{2}}}\)
9. Acids react with bases to form salt and water along with the production of heat. The reaction of an acid with a base to form salt and water is called a neutralisation reaction.
   \(\begin{array}{*{20}{c}}
   {\mathop {{\rm{NaOH}}}\limits_{{\rm{Sodium}}\,{\rm{hy}}\,{\rm{droxide}}} }& + &{\mathop {{\rm{HCl}}}\limits_{{\rm{Hydrochloric}}\,\,{\rm{acid}}} }& \to &{\mathop {{\rm{NaCl}}}\limits_{{\rm{Sodium}}\,\,{\rm{choride}}} }& + &{\mathop {{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{Water}}} } \end{array}\)

In the above reaction, the acid and the base neutralise each other to form a neutral salt.

How are Acids formed?

Acids are formed in small amounts in nature. When required in large quantities, they are prepared by artificial methods. Acids are generally made by dissolving oxides of non-metals (e.g., carbon, sulphur and nitrogen) in water. These oxides are called acidic because when dissolved in water, they form acids.

\({{\rm{H}}_{\rm{2}}}{\rm{O + C}}{{\rm{O}}_{\rm{2}}} \to {{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}}\)

\({\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\)

Uses of Acids

Mineral acids find wide application in various industries and natural acids, mainly in food processing.

1. Our body requires some acids for various chemical processes taking place inside the body cells.
2. Hydrochloric acid is used as a bathroom cleaner in the tanning of leather, dyeing and textile industries.
3. Vinegar contains acetic acid, which is used as a food preservative. Food is pickled in vinegar. This prevents it from getting spoilt. Vinegar also adds flavour to foods.
4. Tartaric acid is used as a component of baking powder.
5. Citric acid is used as a flavouring agent and food preservative.
6. Nitric acid is used to make fertilisers, explosives, dyes, and pharmaceuticals.
7. Hydrochloric acid, fertilisers, medicines, detergents, and explosives are all made with sulphuric acid, which is utilised in lead storage batteries.

Bases

If we take some baking soda and taste it, it appears to have a bitter taste. And if we rub a solution of baking soda between our fingers, it feels soapy to touch (or slippery to touch). The substances (such as baking soda) which are bitter in taste and feel soapy to touch are known as bases. Bases are the chemical opposites of acids. When bases are added to acids, they neutralise (or cancel) the effect of acids. We can now define bases as follows:

A substance that can neutralise an acid to form a salt (and water) is called a base. Bases have a bitter taste. Bases turn red litmus to blue. Examples of bases are sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide.

A base that is soluble in water is called an alkali. All the bases we have given above are soluble in water, so all of them are alkalis.

1. Soap contains sodium hydroxide and potassium hydroxide.
2. Calcium hydroxide is found in lime water.
3. Magnesium hydroxide is found in the milk of magnesia.

Types of Bases

Bases can be classified into two types:

1. Strong bases and
2. Weak bases

1. Strong bases: A base that completely ionizes in water and thus produces a large number of hydroxides ions is called a strong base. Examples: Sodium hydroxide, potassium hydroxide.
2. Weak bases: A weak base produces a low concentration of hydroxyl ions in an aqueous solution. Examples: Ammonium hydroxide, lead hydroxide.

Properties of Bases

Bases are usually oxides and hydroxides of metals. Bases show some properties as follows:

1. Bases are bitter in taste and soapy to touch.
2. Bases turn red litmus paper blue.
3. Bases are corrosive in nature and cause burn injury to the skin.
4. Bases react with acids to form salts, which is a neutral substance. The reaction involved is the neutralisation reaction.
5. Bases are described by the presence of hydroxyl group \(\left( { – {\rm{OH}}} \right)\).
6. Bases soluble in water are called alkalis.

How are Bases formed?

Bases are generally formed in the following ways.

1. By the direct combination of a metal with oxygen
   \({\rm{2Mg + }}{{\rm{O}}_{\rm{2}}} \to 2{\rm{MgO}}\)
2. By the action of water or steam on some metals
   \({\rm{2Na + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{2NaOH + }}{{\rm{H}}_{\rm{2}}}\)
3. By the action of heat on some metal carbonates
   \({\rm{CaC}}{{\rm{O}}_{\rm{3}}} \to {\rm{CaO + C}}{{\rm{O}}_{\rm{2}}}\)

Uses of Bases

Uses of bases are as follows:

1. Bases are extensively used in laboratories and many industries.
2. Calcium hydroxide is used for whitewashing. It is also used to neutralise the acidity of the soil.
3. Sodium hydroxide (caustic soda) is used for manufacturing bleaching powder, paper, soaps, synthetic fibres, etc.
4. They are used for neutralising acids and acidic substances. For example, when you have hyperacidity, the doctor gives you an antacid. The antacid is generally a base, e.g., magnesium hydroxide, neutralising the acid.
5. Ammonia is used for manufacturing nitrogenous fertilisers like urea, ammonium sulphate and ammonium nitrate.
6. Coloured oxides of metals like iron, cobalt, chromium and copper are used for making coloured glass.
7. Metal oxides like magnesium oxide, calcium oxide and aluminium oxide melt only at very high temperatures. So, they are used for making refractory bricks. Refractory bricks can withstand high temperatures.

Summary

Acids and bases are crucial chemical molecules that we employ in a variety of ways. For example, our stomach produces an acid (hydrochloric acid) that is required for food digestion; baking soda (sodium hydrogen carbonate) used in bread baking is a base, and salt (sodium chloride) used in cooking is salt. Some acids and bases are found in nature, while others are created artificially in factories. Examples of acids and bases and their properties and applications were covered in this article.

FAQs

Q.1. How do you explain acids and bases?
Ans: Acids are those chemical substances that have a sour taste. Acids change the colour of blue litmus to red. Bases are the chemical opposites of acids. Bases are those chemical substances that have a bitter taste. Bases change the colour of red litmus to blue.

Q.2. What are acid and base?
Ans: An acid is defined as a substance which gives out hydrogen ions when dissolved in water.’ Acids are substances that taste sour and turn blue litmus paper into red.
A base is defined as a substance which gives out hydroxide ions when dissolved in water.’ Bases are substances that taste bitter, feel soapy on touch and turn red litmus paper into blue.

Q.3. What are the two types of acids?
Ans: The two types of acids are organic acids and inorganic acids.

Q.4. What is a simple definition of an acid?
Ans: An acid is defined as a substance which gives out hydrogen ions when dissolved in water.’
Acids that release a larger number of hydrogen ions in water are strong. Inorganic acids like hydrochloric acid, nitric acid and sulphuric acid are strong acids.
Acids that release a few hydrogen ions in water are week acids. Organic acids such as acetic acid, citric acid and tartaric acid are weak acids.

Q.5. Are acids found in the human body?
Ans: Yes, acids play essential roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for the synthesis of proteins required for the growth and repair of body tissues.

Q.6. Write any four properties of acids?
Ans: (i) Acids are sour in taste.
(ii) They are soluble in water.
(iii)All acidic solutions conduct electricity.
(iv) They turn blue litmus red.

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