Bases and alkalis possess distinct physical characteristics that help identify them. These properties include:

1. Most bases are solid at room temperature except ammonia, which is a gas.
2. Soluble bases (alkalis) like NaOH and KOH dissolve in water to form slippery solutions.
3. Bases have a bitter taste (though tasting is not recommended in the laboratory).
4. Strong bases such as NaOH and KOH are corrosive to the skin and can cause burns.
5. Many insoluble bases, such as Cu(OH)₂ and Fe(OH)₃, are colored compounds.
6. Alkalis turn red litmus paper blue.

Bases and alkalis undergo various chemical reactions, such as neutralization and precipitation. Some common reactions include:

1. Reaction with Acids (Neutralization): Bases react with acids to form salt and water.
   $$ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} $$ $$ \text{Ca(OH)}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + 2\text{H}_2\text{O} $$
2. Reaction with Ammonium Salts: Alkalis react with ammonium salts on heating to liberate ammonia gas.
   $$ \text{NH}_4\text{Cl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{NH}_3 $$
3. Reaction with Trioxocarbonates (CO₃²⁻): Strong bases can decompose trioxocarbonates on heating to form metal oxides, water, and carbon dioxide.
   $$ \text{Na}_2\text{CO}_3 + 2\text{NaOH} \xrightarrow{\text{Heat}} 2\text{Na}_2\text{O} + \text{H}_2\text{O} + \text{CO}_2 $$
   $$ \text{CaCO}_3 + 2\text{NaOH} \xrightarrow{\text{Heat}} \text{Ca(OH)}_2 + \text{Na}_2\text{CO}_3 $$

   These reactions show that under certain conditions, strong alkalis can react with trioxocarbonates or bicarbonates, forming hydroxides or oxides along with the evolution of carbon dioxide.

4. Reaction with Metal Ions (Precipitation Reaction): Insoluble metal hydroxides are formed when alkalis react with soluble metal salts.
   $$ \text{FeCl}_3 + 3\text{NaOH} \rightarrow \text{Fe(OH)}_3 + 3\text{NaCl} $$ $$ \text{CuSO}_4 + 2\text{NaOH} \rightarrow \text{Cu(OH)}_2 + \text{Na}_2\text{SO}_4 $$

Bases and alkalis can be prepared through various methods depending on their solubility and reactivity.

1. Reaction of Metals with Water: Some reactive metals (like sodium and potassium) react with water to form their hydroxides and release hydrogen gas.
   $$ 2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2 $$ $$ 2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2 $$
2. Reaction of Metal Oxides with Water: Some metallic oxides dissolve in water to form alkalis.
   $$ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 $$ $$ \text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH} $$
3. Double Decomposition: Soluble hydroxides can be obtained by reacting soluble salts of alkalis with soluble hydroxides.
   $$ \text{FeCl}_3 + 3\text{NH}_4\text{OH} \rightarrow \text{Fe(OH)}_3 + 3\text{NH}_4\text{Cl} $$ $$ \text{CuSO}_4 + 2\text{NaOH} \rightarrow \text{Cu(OH)}_2 + \text{Na}_2\text{SO}_4 $$
4. By Electrolysis of Brine: Sodium hydroxide is industrially prepared by the electrolysis of concentrated sodium chloride (brine) solution.
   $$ 2\text{NaCl} + 2\text{H}_2\text{O} \xrightarrow{\text{Electrolysis}} 2\text{NaOH} + \text{Cl}_2 + \text{H}_2 $$

Bases and alkalis have numerous industrial, domestic, and medical applications. Some common bases and their uses are shown in the table below: