Indicators and pH

Indicators

Indicators are substances that change colour depending on the acidity or alkalinity of a solution.

Litmus is a common indicator; it turns red in acidic conditions and blue in alkaline conditions.
Universal indicator provides a wider range of colours, from red for strongly acidic, through green for neutral, to purple for strongly alkaline.
Phenolphthalein is colourless in acidic solutions and pink in alkaline solutions.

The pH scale is a measure of acidity or alkalinity, ranging from 0 to 14.

A pH value of 7 represents a neutral substance, like pure water.
Solutions with a pH less than 7 are acidic. The lower the pH, the stronger the acid.
Solutions with a pH greater than 7 are alkaline (or basic). The higher the pH, the stronger the alkali.
Each unit change in pH represents a tenfold change in acidity or alkalinity.

Acid-base reactions result in the formation of a salt and water, and a change in pH.

An acid reacts with a base to produce a salt and water, a process known as neutralisation.
Neutralisation reactions are exothermic; they release energy in the form of heat.
In an aqueous solution, acids donate protons (H+ ions), while bases accept protons.
Strong acids and bases ionise completely in water, whereas weak acids and bases ionise only partially.

Understanding pH and indicators has many real-life applications.

pH is an important factor in ecological systems and agriculture. Knowing the pH of soil, for example, can influence what types of plants can grow effectively.
In medicine, the pH of blood and other bodily fluids is closely regulated. Changes in pH can indicate disease or infection.
Many cleaning products are either acidic or alkaline, taking advantage of the pH-dependent reactivity to break down dirt and grime.
pH also plays a crucial role in certain aspects of cooking and food preservation.