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How Strong are Acids and Bases on pH Scale?

  • Last Updated : 29 Nov, 2021

Every chemical substance we come across has some form of nature, just as we humans do. However, when it comes to chemicals, we associate nature with acidic, basic, or neutral states. Acids, bases, and salts have an impact on chemistry as well as our daily lives. Acids have a sour flavour, bases have a bitter taste, while salts themselves have a salty taste.

Many acids and bases that we do not use in our daily lives are utilized in laboratories and industries, such as HCl, H2SO4, and NaOH, KOH, among others. The neutralization process results in the creation of salt and water when these acids and bases are mixed in the proper quantities. NaCl and KCl, for example, are naturally occurring salts found in seawater and natural rock deposits.

What are Acids?

The term acid is derived from the Latin word ‘acidus’ or ‘acere’, which means sour. The most common characteristic is their sour taste. An acid is a substance that renders ionizable hydronium ion (H3O+) in its aqueous solution. It turns blue litmus paper red

Acids can be present in a variety of things, including food, but their presence in several fruits is particularly notable. For example:-

  • Curd – Lactic Acid
  • Vinegar – Acetic Acid
  • Orange – Citric Acid
  • Tamarind – Tartaric Acid
  • Tomato – Oxalic Acid
  • Lemon – Citric Acid

Apart from these, several acids, such as hydrochloric acid, sulphuric acid, and nitric acid, are commonly employed in laboratories. In the stomach, we have certain fairly common acids, such as weak hydrochloric acid, which causes food indigestion. We normally experience indigestion and a burning feeling in our stomach when the contents of our stomach become excessively acidic. When acids react with metals, hydrogen gas is produced. All acids have hydrogen as a component.

Metal + Acid ⇢ Salt + Hydrogen

Properties of Acids

  • When an acid is dissolved in water, it produces hydrogen ions (H+).
  • Acids react with metals to form/release hydrogen gas.
  • Acid has a sour flavour and is caustic in nature.
  • Acids have a pH of less than 7.
  • When acids react with limestone (CaCO3), carbon dioxide is produced.
  • Blue litmus paper is generally converted to red litmus paper by acid.
  • They obliterate bases’ chemical properties.

Classifications of Acids 

On the basis of Origin:

  • Organic Acids – The acids that come from organic matter like plants and animals are known as Organic Acids. For Example, citric acid (Citrus fruits), Acetic acid (Vinegar), Oleic acid (Olive oil), etc.
  • Mineral Acids – The acids that come/are produced from minerals are known as Mineral Acis or Inorganic Acids. These acids do not contain carbon For Example H2SO4, HCl. HNO3, etc.

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

  • Strong Acids – A strong acid is one that can be totally or nearly completely dissociated in water. For Example, Sulphuric acid, Nitric acid, Hydrochloric acid, etc.

H+ + H2O ⇢ H3O+

HCl(aq)  ⇢ H+(aq) + SO4-(aq)

H2SO4(aq) ⇢  2H+(aq) + SO4-(aq)

  • Weak Acids – A weak acid is one that does not completely dissociate or dissociate very little in water. For Example, the acids that we consume on daily basis like citric acid, acetic acid, etc.

CH3COOH(aq) ⇢ CH3COO-(aq) + H+(aq)

HCOOH(aq) ⇢ HCOO-(aq) + H+(aq)

What are Bases?

Bases are ionic substances that when dissolved in water produce negative hydroxide (OH) ions. An ionic compound is one that contains a negative nonmetal ion and a positive metal ion that is held together by an ionic bond.

Properties of Bases

  • Bases are chemicals that, when dissolved in water, produce the hydroxide ion (OH).
  • Bases have a harsh taste and caustic properties. They frequently have a slick, soapy feel about them.
  • Bases are excellent conductors of electricity and have a pH of more than 7.
  • Soap molecules are formed when bases combine with oils and grease.
  • Red litmus paper is converted to blue litmus paper by bases.
  • Bases have a proclivity for corroding metal surfaces.
  • When they come into contact with acids, they respond quickly.

Classification of Bases

  1. Strong Bases – In the acid-base reaction, a strong base is described as a basic chemical substance that can remove a proton (H+) from (or deprotonate) a molecule of even a relatively weak acid (like water). Hydroxides of alkaline earth metals and alkali metals, such as Ca(OH)2 and NaOH, are two common examples of strong bases. A few of the bases, such as alkaline earth hydroxides, can be employed when the solubility requirement is ignored due to their poor solubility. “Several antacids were suspensions of the metal hydroxides like magnesium hydroxide and aluminium hydroxide,” says one proponent of the low solubility. For Example – Sodium hydroxide – NaOH, Lithium hydroxide – LiOH, Potassium hydroxide – KOH.
  2. Super Bases – Because their conjugate acids, amines, stable hydrocarbons, and dihydrogen, are extremely weak, Group 1 salts of hydrides, amides, and carbanions tend to be stronger bases. In general, these bases are made by mixing conjugate acid with pure alkali metals like sodium. They are known as superbases, and keeping them in water is nearly impossible because they are classified as stronger bases than the hydroxide ion. As a result, conjugate acid water is deprotonated. For Example – Sodium hydride (NaH), Sodium amide (NaNH2), and Butyl lithium (n-C4H9Li).
  3. Weak Bases – A weak base is one that does not completely ionize in an aqueous solution or one whose protonation is incomplete. At 25 °C, the equilibrium constant for the above-mentioned reaction is 1.8 x 10-5, implying that the degree of ionization or reaction is quite minimal.
  4. Lewis Bases – A Lewis base, also known as an electron-pair donor, is a molecule that has a high-energy pair of electrons that can be shared with a low-energy empty orbital in an acceptor molecule to form an adduct. Other possible acceptors (known as Lewis acids) include neutral molecules like BF3 and metal ions like Fe3+ or Ag+, in addition to the H+ molecule. Adducts containing metal ions, on the other hand, are known as coordination complexes. An electric stress state occurs when a neutral base forms a bond with a neutral acid, according to the original Lewis formulation. The electron pair that used to belong only to the base is now shared by acid and base.

pH

Soren Peter (Biochemist) was the first to coin the term pH in 1909. We utilize a universal indicator to determine the strength of acids and bases, which shows distinct colours at varying quantities of hydrogen ions in a solution. The pH value is commonly used to determine the strength of acid and base in a quantitative manner. The logarithm of H+ ion concentration is defined as pH, which stands for Power of Hydrogen. Any material or solution’s pH value indicates whether it’s acidic, neutral, or alkaline.

What is the pH scale?

A pH scale is a tool for determining acid and base concentrations. The scale goes from zero to fourteen, with zero being the lowest and fourteen being the highest. A litmus test reveals whether a substance is acidic or basic. The colour of the paper matches the pH scale numbers, indicating the sort of chemical being tested. 

What is pH value?

A pH scale is used to determine the pH value of a component. The pH scale ranges from 0 to 14, with 0 indicating extremely acidic and 14 indicating extremely alkaline. If a pH value of 7 is found in any solution, it indicates that the solution is neutral in nature. Values less than 7 suggest an acidic solution, whereas values more than 7 indicate an alkaline solution. The acidity of the solution increases as the pH value decreases from 7 to 1, i.e. a solution with a pH value of 2 is more acidic than a solution with a pH value of 3. The alkalinity of a solution increases from 7 to 14 (in the opposite direction of acidity), i.e. a solution with a pH of 11 is more alkaline than a solution with a pH of 9.

Strength of Acid: pH 

Acids are defined as substances with a pH less than 7.0. As the amount of H+ ion in the solution increases, the value decreases. Strong acids are compounds that rapidly release H+ ions or are completely ionizable in solution. As a result, strong acids have a lower pH value, close to 0 to 1. The higher the concentration of H+ ions in the solution, and hence the stronger the acid, the lower the pH value.

For example, Hydrochloric acid, Sulfuric acid, Nitric acid, Perchloric acid, Chloric acid, etc.

A weak acid is one that does not entirely ionize in solution. In low quantities, it releases the H+ ion, resulting in a pH range of 5 to 7. Formic acid (HCOOH), acetic acid (CH3COOH), and many more acids are examples.

Strength of Base: pH

The nature of certain substances is determined by their pH. Bases, on the other hand, are substances having a pH greater than 7.0. As the amount of H+ in the solution drops, the value continues to rise. Strong bases are chemicals that rapidly release the OH- ion in a solution. The H+ ion in the solution is scooped up by these ions, which raises the pH value of the solution. As a result, strong bases commonly have pH values of around 13 or 14.

For example – Lithium hydroxide, Sodium hydroxide, Potassium hydroxide, Rubidium hydroxide, Cesium hydroxide, etc.

The chemicals that do not completely dissociate are known as weak bases( have a pH value in the range of 7 – 10). As a result, the concentration of OH- ions decreases, and the pH value rises.  Methylamine and ammonia are two such examples.

Sample Questions

Question 1: How can one differentiate between an Acid and a Base?

Answer:

Acid and Bases can be differentiated by using a litmus paper. Litmus paper/solution turns red in acidic solutions and blue in alkaline solutions. 

Question 2: List some acids present in fruits and vegetables.

Answer:

 Orange – Citric Acid

Tamarind – Tartaric Acid

Tomato – Oxalic Acid

Lemon – Citric Acid

Question 3: Acids react with metals to release which gas?

Answer:

Acids react with metals to release hydrogen gas.

Question 4: Between Acids and Bases which is a good conductor of electricity?

Answer:

Bases are excellent conductors of electricity and have a pH of more than 7.

Question 5: What is the pH range of Acid and Base?

Answer:

Solutions with pH less than 7 are acidic in nature, whereas solutions with pH higher than 7 are basic in nature.

Question 6: Explain strong acid with pH range.

Answer:

 Strong acids are compounds that rapidly release H+ ions or are completely ionizable in solution. As a result, strong acids have a lower pH value, close to 0 to 1. The higher the concentration of H+ ions in the solution, and hence the stronger the acid, the lower the pH value.

For example – Hydrochloric acid, Sulfuric acid, Nitric acid, Perchloric acid, Chloric acid, etc.

Question 7: Explain a strong base with a pH range.

Answer: 

Strong bases are chemicals that rapidly release the OH- ion in a solution. The H+ ion in the solution is scooped up by these ions, which raises the pH value of the solution. As a result, strong bases commonly have pH values of around 13 or 14.

For example – Lithium hydroxide, Sodium hydroxide, Potassium hydroxide, Rubidium hydroxide, Cesium hydroxide, etc.


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