When base react or dissolve in water it dissociate into hydroxide ions.

When a base reacts with water, the following processes occur:

1. Dissociation of the base:
- The base molecules break down into their respective ions when they come into contact with water.
- For example, if we consider the reaction of sodium hydroxide (NaOH) with water, it dissociates into sodium ions (Na+) and hydroxide ions (OH-).
- This dissociation process allows the base to participate in further reactions with the water molecules.

2. Proton transfer:
- The hydroxide ions (OH-) that are produced from the dissociation of the base act as proton acceptors.
- Water molecules act as proton donors, releasing a hydrogen ion (H+).
- The hydroxide ions accept the hydrogen ions, forming water molecules.

3. Formation of the conjugate acid:
- As a result of the proton transfer, the hydroxide ions accept the hydrogen ions and form water, while the water molecules donate the hydrogen ions.
- This leads to the formation of the conjugate acid of the base.
- In the case of sodium hydroxide, the conjugate acid formed is water.

4. Formation of hydroxide ions:
- The base also contributes to the production of hydroxide ions in the solution.
- The hydroxide ions produced from the dissociation of the base and the hydroxide ions formed from the proton transfer combine to increase the concentration of hydroxide ions in the solution.

5. Change in pH:
- The reaction of a base with water results in an increase in the concentration of hydroxide ions (OH-) in the solution.
- This increase in hydroxide ion concentration leads to a decrease in the concentration of hydrogen ions (H+), consequently increasing the pH of the solution.
- The pH scale ranges from 0 to 14, with values below 7 indicating acidity, 7 indicating neutrality, and values above 7 indicating alkalinity (basicity).

In summary, when a base reacts with water, it dissociates into ions, the hydroxide ions accept hydrogen ions to form water, and the base contributes to the production of hydroxide ions. This reaction results in the formation of the conjugate acid of the base and an increase in the pH of the solution.