Acids and bases- Some important indicators

Introduction:

The world around us works on scientific principles. Acids and bases are special classes of chemical compounds that exhibit various interesting reactions. Many natural occurring events could be explained with a decent understanding of acid and base reactions. Various citrus fruits contain citric acid, often referred to as Vitamin C. Vinegar, which is effectively used in food, is a type of acid known as acetic acid. Milk turns sour due to the development of lactic acid. Thus, many reactions around us could be explained with the help of acid and base relations. The article hence describes various acid-base mechanisms about the real-world reactions.

What is an acid?

Scientists have used the word acid for quite a long time. What does the word mean? The word acid is derived from the Latin word ‘acere’, which means sour. Thus acids are oftentimes simply described as sour-tasting (do not taste an acid) chemical compounds. A more scientific definition would be: An acid is a hydrogen-based compound that can donate a proton to another substance. The proton donated by an acid to another compound, that  is a hydrogen ion (H+). Even after the loss of the H+ ion, the acid remains energetically stable. An acidic compound turns blue litmus red and shows no effect on red litmus.

                                       H2O(l) ⇌ OH−(aq) + H+(aq) (Hydrogen ion)

What is a base?

In contrast to acids, bases possess a bitter taste (do not taste any base) and a somewhat slippery texture. A base is defined as a chemical compound capable of accepting the proton donated by the acid. Thus the base accepts the hydrogen atom donated by the acid. The bases which are soluble in water are referred to as alkalis. When a base reacts with another acid, the product is a base. Bases turn red litmus blue and show no effect on blue litmus.

                                          2H2O → H3O+ + OH– (Base)

Neutralisation reactions: reactions between an acid and a base

Neutralisation reactions are reactions between an acid and a base that lead to the production of salt and water. During a neutralisation reaction, the H+ ions of the acid react with OH– ions of a base to form water, and other ions indulged in the reaction form a salt.

Different theories related to acids and bases:

The different theories related to acids and bases attempt to define the nature of different acids and bases. The Arrhenius theory, the Bronsted-Lowry theory, and the Lewis theory of acids and bases are some theories to define the chemical compounds.

Arrhenius theory: This theory of acids and bases states that an acid generates H+ ions in the solution, whereas a base generates OH– ions in a solution.

Bronsted-Lowry theory: The Bronsted-Lowry theory states that acid can be defined as a proton donor, whereas the base can be defined as a proton acceptor.

Lewis theory of acids and bases: According to the Lewis theory of acids and bases acids are electron-pair acceptors, and bases are electron-pair donors.

The pH of acids and bases:

The acidity or basicity of a substance or simply the strength of an acid or base can be defined by the pH value of the acid or base. pH stands for the potential of hydrogen.

According to the pH value of various acids and bases, their strength can be measured on a pH scale of 0 to 14. The numeric value of the strength of an acid or base on a pH scale determines its acidity or basicity. The pH value is the most trusted way to measure the strength of an acid or base. On a pH scale, an acid is stronger if it has a lower pH value. In the case of a base or a base with a higher pH value is stronger than the others.

Properties of acids and bases:

Properties of acids:

• Acids are corrosive
• They are good conductors of electricity
• When reacted with bases, they produce salt and water
• The pH value of acid is always less than 7
• A lower PH value signifies an acid of greatest strength
• When an acid reacts with the metal, it produces hydrogen gas
• Acids are generally sour-tasting (do not taste an acid).

Examples: hydrochloric acid acetic (HCl), sulfuric acid (H2SO4)

Properties of a base:

• Bases have a soapy texture
• They taste bitter
• Bases produce hydroxide ions when they are dissolved in water
• Bases act as good conductors of electricity if they are in an aqueous solution
• The pH value of a base is more than 7
• The larger the pH value of a base, the greater the strength
• Some bases are soluble in water, and hence they are called alkalis.

Example: sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2)

Common Indicators of acids and bases:

Litmus paper: acids turn blue litmus red and have no effect on red litmus; bases turn red litmus blue and do not affect blue litmus

Methyl orange: acids turn methyl orange into red; bases turn methyl orange into yellow

Phenolphthalein: acids do not change the colour of colourless phenolphthalein; bases turn Phenolphthalein pink or red.

Red cabbage water: acids turn red cabbage water to red or pink; bases turn red cabbage water to blue, green or yellow.

Conclusion

In conclusion, acids and bases are special chemical compounds that cause many environmental reactions around us. An acid reacts with a base to produce salt and water, participating in a neutralisation reaction. The strength of an acid or base can be defined by its numerical value on the pH scale; indicators can be used to differentiate an acid from a base.