Acid and Base Strength: pH Scale Overview

The strength of acid and base solutions is determined by their concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻), respectively. The pH scale acid and base is commonly used to express this strength. The pH scale ranges from 0 to 14, with lower values indicating acidic solutions, higher values indicating basic solutions, and 7 being neutral (pure water). 

Decoding Acid and Base: Universal Indicators

• Use of Indicators: To judge how strong a given acid and base is, we use a universal indicator, which is a mixture of several indicators. 
• Colour Differentiation: The universal indicator of acid and base shows different colours at different concentrations of hydrogen ions in a solution.

Exploring the pH Scale: Acid and Base Evaluation

• It is a scale for measuring hydrogen ion concentration in a solution, called pH scale.
  • The p in pH stands for ‘potenz’ in German, meaning power. 
• Scale Measurement: The pH scale can measure the acidity, ranging generally from 0 (indicating very acidic) to 14 (indicating very alkaline), providing a comprehensive assessment of acid and base levels in a solution.
  • Higher the hydronium ion concentration, lower is the pH value.
  • The pH of a neutral solution is 7 whereas values less than 7 on the pH scale represent an acidic solution.
  • As the pH value increases from 7 to 14, it signifies a rise in OH– ion concentration in the solution, indicating an escalation in the strength of base, emphasizing the fundamental relationship between pH levels and the varying strengths of acid and base in the solution. 
• Measurement: Generally paper impregnated with the universal indicator is used for measuring pH of acid and base.
• Strength: Acids that yield a higher concentration of H+ ions are categorized as strong acids, while those producing fewer H+ ions fall under the classification of weak acids, exemplifying the diverse characteristics between acid and base strengths.

Acid and Base Dynamics: Life and Environment

• Plants and animals: The significance of acid and base balance is evident in everyday life, particularly for plants and animals. The human body functions within a critical pH range of 7.0 to 7.8, emphasizing the essentiality of maintaining acid and base equilibrium. 
• Living organisms can survive only in a narrow range of pH change. 
  • When pH of rain water is less than 5.6, it is called acid rain. 
  • When acid rain flows into the rivers, it lowers the pH of the river water. 
  • Thus, the survival of aquatic life in such rivers becomes difficult.
• pH of the Soil: The significance of acid and base can be seen in plants that require a specific pH range for their healthy growth.
• pH in our Digestive System: Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach, showcasing the remarkable balance between acid and base necessary for effective and safe digestive processes.
• pH Change as the Cause of Tooth Decay: Tooth enamel, made up of calcium phosphate is the hardest substance in the body. 
  • It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. 
  • Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. 
  • Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.
• Self Defence by Animals and Plants Through Chemical Warfare: Bee-sting leaves an acid which causes pain and irritation. 
  • Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain.

Neutralisation: Balancing Act of Acid and Base

• Meaning: When an acidic solution is mixed with a basic solution, both the solutions neutralise the effect of each other. This interaction demonstrates the capacity of acid and base substances to counteract and balance their respective properties when combined.
  • The resulting solution is neither acidic nor basic. 
• Salt: In a neutralisation reaction a new substance is formed called salt. 
  • Salt may be acidic, basic or neutral in nature.
• Neutral: Thus, the reaction between an acid and a base is known as neutralisation. 
  • Salt and water are produced in this process with the evolution of heat.

              Acid + Base → Salt + Water (Heat is evolved)

• Example: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium Chloride (NaCl) + Water (H2O)

• + Water (H2O)

Neutralisation in Practical Situations: Acid and Base Harmony

• Indigestion: Our stomach contains hydrochloric acid which helps us in digesting food. 
  • But too much acid in the stomach causes indigestion. 
  • During indigestion the stomach produces too much acid and this causes pain and irritation. 
  • To get rid of this pain, people use bases called antacids such as milk of magnesia, which contains magnesium hydroxide which neutralises the effect of excessive acid.
• Ant Bite : Ant bites inject the acidic liquid (formic acid) into the skin. 
  • It can be neutralised by the rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate. This showcases the effective use of acid and base reactions to mitigate the effects of ant bites on the skin.

• Soil treatment: Plants do not grow well when the soil is either too acidic or too basic.
  • Soil Acidification: Excessive use of chemical fertilizers makes the soil acidic. 
  • Use of Quicklime: When the soil is too acidic, it is treated with bases like quicklime (calcium oxide) or slaked lime (calcium hydroxide). 
  • When the soil is basic, organic matter (compost) is added to it which releases acids and thus neutralises the basic nature of the soil. This process demonstrates the role of acid and base interactions in adjusting the soil’s pH levels for optimal conditions.
• Factory wastes: The wastes of many factories contain acids and the flow of these waste into the water bodies can kill fish and other organisms. 
  • The factory wastes are, therefore, neutralised by adding basic substances.