What are Acids?

Acids are a molecule or other species which can donate a proton or accept an electron pair in reactions. The word “acid” is derived from the Latin word “acidus” which means sour.

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All acid elements have a few things in common i.e all are sour in taste, they turn blue litmus paper to red, and lose their acidity if they’re combined with alkaline substances.

The pH level of acids ranges from 0 – 6.

Some common examples of acids are Citrus fruits such as lemons, limes, oranges, grapefruit, etc. All these fruits contain citric acid. Hence, they taste sour or tart.

Citric acid is a weak acid but still, it produces hydrogen ions when mixed with water and that’s why the pH of lemon juice is 2. 

Another example of an acid is vinegar. Vinegar consists of acetic acid. Ever wondered why your skin becomes red and swollen after an ant bite or a mosquito bite?

Because these insects inject formic acid which causes such skin reactions. Nitric acid, sulfuric acid, hydrochloric acid, etc. are other common ones.

Properties of Acids

The properties of Acids are as follows;

  • Acids change the color of blue litmus to red
  • They change the color of Methyl Orange/Yellow to Pink
  • Acidic substances converts Phenolphthalein from deep pink to colorless
  • Are sour or tart in taste
  • The pH level of acids range from 0-6
  • Acids lose their acidity when combined with alkalines
  • They destroy the chemical property of bases
  • When reacting with metals they produce hydrogen gas
  • Acids produce carbon dioxide when reacted with carbonates.
  • Most acids are corrosive in nature which means that they tend to corrode or rust metals.

Classification of Acids

Acids are often classified on the basis of source, the presence of oxygen, strength, concentration and basicity.

Classification based on the source

This means that the acid is classified on the basis of their source or origin. They are mainly of two types: Organic acid and Mineral acid.

  • Organic Acid: This is the acid obtained from organic materials such as plants and animals. For e.g. Citric acid (Citrus fruits), Acetic acid (Vinegar), Oleic acid (Olive oil), etc.
  • Mineral Acid: Mineral acid is procured from minerals. They are also known as inorganic acids. They do not contain carbon. For e.g.  H2SO4, HCl. HNO3, etc.

Classification based on the presence of Oxygen

This means that the acids are classified on the basis of the presence of oxygen. These are of two types: Oxy-acid and Hydracids.

  • Oxy-acid: Acids that consist oxygen in their composition is known as Oxy-acids. For e.g. H2SO4, HNO3, etc.
  • Hydracid: Those that consist hydrogen combined with other elements and do not contain any oxygen in their composition and do not contain any oxygen in their composition are called Hydracids. For e.g. HCl, HI, HBr, etc.
what are acids
what are acids

Classification based on the Strength of the acid

Acids produce hydrogen ions when mixed with H2O, the strength of an acid depends on its concentration of the hydrogen ions present in a solution. A greater number of hydrogen ions means greater strength of the acid whereas, lower number of hydrogen ions means that the acid is weak. They are classified as :

  • Strong Acids: An acid which can be dissociated completely or almost completely in water is known as a strong acid. For e.g.  sulphuric acid, nitric acid, hydrochloric acid, etc

H+ + H2O <—-> H3O+

 HCl(aq)  <—-> H+(aq) + SO4-(aq)

 H2SO4(aq) <—> 2H+(aq) + SO4-(aq)

  • Weak Acids: An acid which doesn’t dissociate completely or dissociates negligibly in water is known as a weak acid. For e.g. Those that which we usually consume on daily basis i.e. citric acid, acetic acid, etc

CH3COOH(aq) <—–> CH3COO-(aq) + H+(aq)

HCOOH(aq) <—> HCOO-(aq) + H+(aq)

Classification based on its concentration

As we have studied above, the concentration of the acid depends on the number of hydrogen ions that it produces in water. Based on this the acid is classified as :

  • Concentrated Acid: When an aqueous solution has a relatively high percentage of acid dissolved in it, then it is a concentrated acid. For e.g. concentrated hydrochloric acid, concentrated sulphuric acid, concentrated nitric acid, etc,
  • Diluted Acid: When an aqueous solution has a relatively low percentage of acid dissolved in it, then it is a dilute acid. For e.g. dilute hydrochloric acid, dilute sulphuric acid, dilute nitric acid, etc.

Classification based on the basicity of the acid

Acid on dissociation in water produces hydrogen ion. The number of these hydrogen ions that can be replaced in an acid is the basicity of an acid.

  • Monobasic Acid: A monobasic acid is an acid which has only one hydrogen ion. Therefore, these acids combine with one hydroxyl group of the base to form salt and water.  For e.g. HCl, HCOOH, HBr, etc
  • Dibasic Acid: Dibasic acid is that which shares twp hydroxyl groups it is known as dibasic acid. Dibasic acid dissociates in 2 steps. They can provide 2 kinds of salts i.e. the normal salt and a hydrogen salt

H2SO4(aq) <—> H+(aq) + HSO-4(aq)

2NaOH(aq) + H2SO4(aq) <—-> Na2SO4(aq) + 2H2O(l)

  • Tribasic Acid: Tribasic acids are those which can combine with three hydroxyl groups. They have three replaceable hydrogen ions, and they produce 3 types of salts. For e.g. H3PO4

NaOH(aq) + H3PO4(aq) <—> NaH2PO4(aq) + H2O(l)

2NaOH(aq) + H3PO4(aq) <—> Na2HPO4(aq) + 2H2O(l)

Q: The characteristic properties of an acid is due to the presence of ___________

  1. hydride ions
  2. hydroxly ions
  3. hydronium ions
  4. oxide ions

Sol: The correct answer is option ‘c’. The acid in aqueous solution gives H+ ion which combines with water to form hydronium ions (H3O+). Hence, acid is characterised by the presence of hydronium ions.

Acids and Bases We Use In Everyday Life

Acids and Bases are encountered daily in chemistry and our everyday life. Both Acids and bases make the critical part and parcel of our livelihood. They play an efficient role inside or outside of our body. From the formation of the food to the decomposition of any substance, acids and bases play a crucial role in our everyday life. Let’s check their uses in our daily life.

Acids used in everyday life

The name acid gives us sensory images of – Sourness. They are the chemical substances; ranging in pH scale from 0 to 7. Acids are common chemicals and can be found everywhere even in our food. Let’s check its everyday uses.

1. Hydrochloric Acid (HCl)

Hydrochloric acid is the strong acid which is found inside our body in the gastric juice. It helps in the breakdown of all the potatoes and pizzas we eat and turns down the enzymes, which change the food particles into protein. HCl is also used in the formation of many organic compounds like Polyvinyl Chloride and some pharmaceutical drugs.

2. Acetic Acid

The most common form of acetic acid is vinegar. It is a popular home staple, which is found in most of the kitchens. People use it for cooking purposes, and this is what gives the salad a delicious taste and pickled vegetables and fruits, their- tart taste.

3. Ascorbic or Citric Acid 

Citric acids are found in fruits like oranges, lemon, and other citrus fruits. It is widely used as an acidifier and flavouring agent of food. Citric acids are also used in destaining the cloth.

4. Carbonic Acid

When it is too hot, surely most of us would try to find something refreshing to feel relieved like drinking soda or cold drinks. These are the carbonated drinks which, are made by adding carbon dioxide in water. When carbon dioxide reacts with water under a certain pressure, it makes carbonic acid, which causes a refreshing sensation.

5. Sulphuric Acid 

Sulphuric acid is a strong acid whose single drop can cause a hollow mark in your skin. Apart from its too dangerous property, it has numerous applications. The most common application is the Sulphuric acid found in the car batteries. It is also used in making fertilizers, cleaning products, and manufacturing of polymers. Iron and steel industries use sulfuric acid to remove oxide coatings. It is also used in some solution to unclog the drain.

6. Tartaric Acid

The food industry uses tartaric acid as an additive and flavoring agent. This acid is obtained mostly from fruits like grapes and is mainly used in the manufacturing of wine. It is also used as a food preservative and in settings of gel or jellies.

Bases used in Everday Life

Bases are the chemical compounds, which are soapy in touch and are not usually meant for human consumption. They have a wide range of applications in our daily life. Let’s check some of them.

1. Sodium Flouride (NaF)

We automatically feel the first base of our day after brushing our teeth. Toothpaste, which we mostly use contains sodium fluoride which is slightly basic in nature. This kills the bacteria present in the mouth, which instead prefer a slightly acidic environment, which is exactly the condition of your unbrushed mouth.

2. Sodium Hydroxide (NaOH)

Everyday we take a bath, but water all alone is not enough to make us feel refreshed. We use soap to clean our body, and these soaps contain sodium hydroxide as their main ingredients. Not only in soaps, all the cleaning products including detergents and washing powder also contain sodium hydroxide.

3. Sodium Bicarbonate 

Sodium bicarbonate, commonly known as baking soda, is the regular item in our kitchens. People use baking soda in cooking, baking cakes. Being a weak base, it is safe for human consumption. A solution of baking soda is commonly used for cleansing purpose. It is also used as fire extinguisher; because in high temperature, it releases carbon dioxide as a by-product.

4. Magnesium Hydroxide 

Magnesium hydroxide is the compounds that are used as anti-acid or for neutralizing the gastric acids. They are used in the antiperspirant deodorant.

5. Calcium Hydroxide 

Calcium hydroxide, commonly referred to as Hydrated/Slaked lime, is widely used in cement manufacturing. It is also used in neutralizing the acidity of the soil and treatment of sewage water. Calcium hydroxide is also an additive feed in improving animal nutrition. It is also used in dental procedures.

6. Ammonia (NH3)

Ammonia is one of the widely used bases in agriculture, industries, and homes. It is one of the ingredients of fertilizers. It is used in eliminating stains and tarnishes of soap from tubs, tiles, floors, and even jewellery.

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