Acid Bases and Salt Animation
Now discuss some common properties of acids with students such as corrosiveness, sour in taste, turns blue litmus paper to a red colour. Also discuss the reactions with other indicators like methyl orange, phenolphthalein and odour changing indicators. Some common physical properties of acids are containing hydrogen ions (H+) in aqueous solution, form salts with base, release H2 gas with metal, and for m CO2, H2O and salt with metal carbonates. Ask the students what happens if we suffer from hyperacidity? Explain that in this situation we should take something that nullifies the effect of the acid. The substance that neutralizes acid is called a base. Solution of a base in water forms an alkali. Discuss some common properties of bases such as corrosive nature, soapy feel, and bitter taste, turns red litmus paper to a blue colour and contains hydroxyl ion.
Ask the students to give some examples of bases such as sodium hydroxide or caustic soda or soap, calcium hydroxide or limewater, ammonium hydroxide or ammonia water, magnesium hydroxide or milk of magnesia etc. Conclude that acids and bases are chemicals which have opposite properties. They nullify each other and may be commonly used in our daily lives. Explain what makes a Strong Acid or Strong Base.
The molecule for a strong acid or base cannot exist intact in aqueous solution. It completely dissociates into ions in water. While weak acids or bases are incompletely dissociated in aqueous solutions and intact molecules of weak acid or base also co-exist with the dissociated ions. Discuss that common salt NaCl, a product of strong acid HCl and strong base NaOH has a pH of 7 and is neutral. Discuss Normal or Neutral Salts which are formed by a strong acid and a strong base. A salt that does not contain any replaceable hydrogen ions is called as a normal salt which is obtained by replacing all the H+ ions of an acid by metal ions or ammonium ions. Other examples of salts are NaCl, Na2SO4, Na3PO4, NH4Cl, K2CO3, CuSO4 etc.