Acids and Bases

• Acids are any substances that form an aqueous solution with a pH less than 7 and reacts with metals
• Bases are any substances with a pH greater than 7 and do not react with metals
• Neutralisation is the reaction between acids and bases to produce salt and water
• The pH scale measures how acidic or alkaline something is, ranging from 0-14
• A strong acid ionises completely. Undergoes complete disassociation in water
• Weak acids dont fully ionise and undergoes partial dissociation in water, establishing an equilibrium , and a solution of weak acid is only a weak electrolyte
• Reaction of an acid with a metal forms salt and hydrogen gas.
• Reaction of an acid and metal hydroxide forms salt and water
• Reaction of an acid with metal oxide forms salt and water
• Reaction of acid and metal carbonate produces salt, water and carbon dioxide
• Reaction of acid with metal hydrogen carbonate forms salt, water and carbon dioxide
• Lower the pH ==> Stronger the acid

  Higher the pH ==> Weaker the acid
• Lower the pH ==> Weaker the base

  Higher the pH ==> Stronger the base
• Hard water is the water containing high amount of minerals of calcium and magnesium
• Soft water is the surface water or chemically softened water
• The main difference between hard water and soft water is that hard water does not form lather with soap, but soft water forms bubbly lather with soap.
• Temporary Hardness is caused by the presence of calcium and magnesium ions in the water. In this case, the hardness in water can be removed by boiling the water.
• Permanent Hardness of water is when the soluble salts of magnesium and calcium are present in the form of chlorides and sulphides in water, we call it permanent hardness because this hardness cannot be removed by boiling
• Disadvantages of Hardness

  • Wastage of soap
  • Wastage of fuel
  • Formation of scales on metallic boilers
• Remove the hardness of water (temporarily)

  • By boiling : Soluble bicarbonates are converted into insoluble carbonates, which are removed by filtration.
  • By clarks method : Calcium hydroxide is Clark’s reagent. It removes the hardness of water by converting bicarbonates into carbonate.
• Common Properties of Acids:

  • They turn blue litmus red
  • They have a sour taste
  • They react with metals to release hydrogen
• Common properties of bases:

  • They turn red litmus blue
  • A base that dissolves in water is called an alkali
• Limitations of the Arrhenius Theory:

  • Limited to aqueous solutions
  • Narrow Definition of Acids and Bases
  • It is the hydronium ion not H+ that exists in the solution
• Hydronium ion formula = H3O+
• Arrhenius , Bronsted-Lowry theory, and Lewis theory are all examples of acid-base theory. They are all based on the idea that the strength of an acid-base reaction is determined by the concentration of the acid or base.
• Bronsted-lowry definition of acids and bases: An acid is any proton donor while a base is any proton acceptor.
• Conjugate acid/base pair is any pair of an acid and a base that differ by the presence of absence 1 proton
• A salt is is formed whenever a hydrogen from an acid is replaced by a metal or ammonium ion
• Neutralisation examples:

  1: Medicine: Antacids contain Sodium Hydrogen Carbonate.

  2: Farming: Calcium Oxide added to acidic soil.

  3: Environmental: Limestone added to acidified lakes

  4: Toothpaste: reacts with the acid produced by bacteria.
• pH indicators are a group of chemical dyes that changes color depending on the pH. Different indicators will change color at different pH's.
• Universal indicator is a dye that changes color in the presence of acid or alkali.
• Factor: Concentration of Hydrogen Ions (H⁺) or Hydroxide Ions (OH⁻)

  • Acidic Solutions:
  • Higher concentration of H⁺ ions
  • Lower pH values
  • Basic Solutions:
  • Higher concentration of OH⁻ ions
  • Higher pH values
• Factor: Temperature

  • Effect on Reaction Rates:
  • Temperature influences the rate of ionization of acids and bases
  • pH-Dependent Chemical Reactions:
  • Some chemical reactions involving protons (H⁺ ions) are temperature-dependent
• Factor: Strength of Acids and Bases

  • Concentration of Strong Acids and Bases:
  • Complete dissociation
  • Higher impact on pH
  • Weak Acids and Bases:
  • Partial dissociation
  • Less pronounced effect on pH
• Soluble ionic compounds are soluble in water because they are made up of ions that are free to move around in the water
• Insoluble ionic compounds are insoluble in water because they are not polar.
• Metals always form cations
• Non-metals always form anions
• Hydroxide ion is a negatively charged chemical compound that contains one hydrogen atom and one oxygen atom, written as OH-