Notes On Strength of Acids and Bases - CBSE Class 10 Science
Neutralization is a chemical reaction in which an acid reacts with a base to form salt and water. In this process, a hydrogen ion of the acid combines with a hydroxide ion of the base to form a water molecule. The anion of the acid combines with the cation of the base to form a salt. For example when hydrochloric acid reacts with sodium hydroxide the chlorine of hydrochloric acid combines with sodium of sodium hydroxide to form sodium chloride. The hydrogen of hydrochloric acid combines with the hydroxyl part of the sodium hydroxide and forms water.  HCl + NaOH → NaCl + H2O Strength of acids or bases: Based on extent of ionization acids and bases are classified into strong acids, weak acids and strong bases, weak bases. Strong acids or strong bases ionizes completly (100%) to form ions in the aqueous solution. Example: Hydrochloric acid ionizes completly to form ions. HCl (aq) → H+(aq) + Cl–(aq) Sodium hydroxide ionizes completly to form ions. NaOH (aq) → Na+ (aq) + OH– (aq) Weak acids or weak bases ionizes partially (<100%) to form ions in the aqueous solution. Example: Acetic acid ionizes partially in aqueous solution to form ions. CH3COOH (aq) ⇔ H+(aq) + CH3COO– (aq) Ammonium hydroxide ionizes partially in aqueous solution to form ions. NH4OH ⇔ NH4+ + OH– (aq) An acid or base is considered as strong or weak depending on the concentration of hydrogen and hydroxide ions within it. This concentration or the power of hydrogen differs from substance to substance and can be measured using a scale, called the pH scale.   A solution that has a pH value of less than 7 is acidic and a solution with a pH value of more than 7 is basic. A neutral solution is indicated by a pH value of 7 on the scale.  Strong acids will posses pH values between 0-2 and weak acids posses pH values more than 3. Strong bases will posses pH values between 12-14 and weak bases posses pH values less than 12. pH of some of the acids and bases: Acid/Base pH Hydrochloric acid  0.1 - 1.0 Sulphuric acid 1.0 - 1.2 Phosphoric acid 1.3 -1.5 Acetic acid (Vineger) 2.9 - 3.0 Carbonic acid 3.8 - 4.0 water 6.9 - 7.0 Ammonia 10.8 - 11.2  Sodium hydroxide 13 - 14 Applications of neutralization concept in daily life:  Antacids like Milk of Magnesia are mild bases that neutralize the acids in the stomach and aid digestion. If the pH lowers, the acidity in the mouth increases and leads to tooth decay.  Toothpastes are basic in nature and they counteract the acid in the mouth. Hydrangea produces pink flowers when the soil has a pH value of 6.8 or higher and blue flowers when the pH value is 6.0 or less. If the soil is acidic, then the applied pesticides, herbicides and fungicides will not be absorbed by the soil. In order to neutralize the soil, suitable bases are used. Generally, salts of calcium or magnesium, which are basic are used to neutralize soil acidity. When a bee stings, formic acid is released. That is what makes the skin burn. Baking soda, which is a base, neutralizes the formic acid and provides relief from the pain.

#### Summary

Neutralization is a chemical reaction in which an acid reacts with a base to form salt and water. In this process, a hydrogen ion of the acid combines with a hydroxide ion of the base to form a water molecule. The anion of the acid combines with the cation of the base to form a salt. For example when hydrochloric acid reacts with sodium hydroxide the chlorine of hydrochloric acid combines with sodium of sodium hydroxide to form sodium chloride. The hydrogen of hydrochloric acid combines with the hydroxyl part of the sodium hydroxide and forms water.  HCl + NaOH → NaCl + H2O Strength of acids or bases: Based on extent of ionization acids and bases are classified into strong acids, weak acids and strong bases, weak bases. Strong acids or strong bases ionizes completly (100%) to form ions in the aqueous solution. Example: Hydrochloric acid ionizes completly to form ions. HCl (aq) → H+(aq) + Cl–(aq) Sodium hydroxide ionizes completly to form ions. NaOH (aq) → Na+ (aq) + OH– (aq) Weak acids or weak bases ionizes partially (<100%) to form ions in the aqueous solution. Example: Acetic acid ionizes partially in aqueous solution to form ions. CH3COOH (aq) ⇔ H+(aq) + CH3COO– (aq) Ammonium hydroxide ionizes partially in aqueous solution to form ions. NH4OH ⇔ NH4+ + OH– (aq) An acid or base is considered as strong or weak depending on the concentration of hydrogen and hydroxide ions within it. This concentration or the power of hydrogen differs from substance to substance and can be measured using a scale, called the pH scale.   A solution that has a pH value of less than 7 is acidic and a solution with a pH value of more than 7 is basic. A neutral solution is indicated by a pH value of 7 on the scale.  Strong acids will posses pH values between 0-2 and weak acids posses pH values more than 3. Strong bases will posses pH values between 12-14 and weak bases posses pH values less than 12. pH of some of the acids and bases: Acid/Base pH Hydrochloric acid  0.1 - 1.0 Sulphuric acid 1.0 - 1.2 Phosphoric acid 1.3 -1.5 Acetic acid (Vineger) 2.9 - 3.0 Carbonic acid 3.8 - 4.0 water 6.9 - 7.0 Ammonia 10.8 - 11.2  Sodium hydroxide 13 - 14 Applications of neutralization concept in daily life:  Antacids like Milk of Magnesia are mild bases that neutralize the acids in the stomach and aid digestion. If the pH lowers, the acidity in the mouth increases and leads to tooth decay.  Toothpastes are basic in nature and they counteract the acid in the mouth. Hydrangea produces pink flowers when the soil has a pH value of 6.8 or higher and blue flowers when the pH value is 6.0 or less. If the soil is acidic, then the applied pesticides, herbicides and fungicides will not be absorbed by the soil. In order to neutralize the soil, suitable bases are used. Generally, salts of calcium or magnesium, which are basic are used to neutralize soil acidity. When a bee stings, formic acid is released. That is what makes the skin burn. Baking soda, which is a base, neutralizes the formic acid and provides relief from the pain.

#### Activities

Activity1: Colorado.edu has developed an interactive simulation about pH concept in three different levels namely macro, micro and cutom. And pH of different solutions and variation in pH with the dilution.This interactive similulation will also helpful to you in knowing the concentrations of hydronium and hydroxide ions and effect of change in their ratio on pH. Go to Activity Activity2: Bgfl.org has created a simulation regarding nature of different indicators in pressence of different compounds using the colour strip.It also helpful in finding ratio of mixing different concentration of acids and bases. Go to Activity

Previous