We use colored solution to detect acidity or basicity of substance in the lab. These substances can be prepared by mixing colored parts of plant body in ethanol (C2H5OH). The color in plant leave is due to the presence of pigments such as chlorophyll and chromoplast. Colored solution is used widely in chemistry to detect acidity and basicity.
pH value of some substances:
Milk of magnesium
HCl = H+ + Cl–
H2SO4 = 2H+ + SO– –4
This hydrogen of an acid can be replaced partially or completely b y metals like zinc and magnesium.
Example: Zinc + Sulphuric acid = Zinc sulphate + Hydrogen
Some common acid:
Name of the acid
Characteristic of Acid:
- Acids posses sour taste.
- Acids turn blue litmus into red.
- Acids neutralize base. HCl + NaOH = NaCl + H2O
- Hydrogen of an acid is displaced by metals. Zn + H2SO4 = ZnSO4 + H2
- Acid produces salt and water when treated with basic oxide CaO + 2HCl = CaCl2 + H2O
- Many carbonates evolve carbon dioxide when treated with acids. E.g. CaO + 2HCl = CaCl2 + H2O
Preparation of Acids
Acids can be prepared by following methods.
1. By direct combination of elements.
H2 + Br2 = 2HBR
2. By action of water on acid anhydride. When acid anhydride is treated with water, corresponding acids are produced.
CO2 + H2O = H2CO3
3. By oxidation of non-metals. When nitric acid acts on phosphorous, and sulphur, phosphoric and sulphuric acids are formed.
P + 5HNO3 = H3PO4 + 5NO2 + H2O