Question

what is an indicator? Name three indicators.​

Answer 1

Answer:

Indicators are substances that show a distinct change (colour or odour) simultaneous to a change in concentration of ions such as H+ and OH- ions. Examples: Methyl orange, phenolphthalein and litmus solution.

Answer 2

Indicators:

They are the materials that change colour (also odour) when added into an acid or an alkaline solution.

Indicators are also classified in the following ways,

• Natural Indicators
• Synthetic Indicators
• Olfactory Indicators
• Universal Indicators

⇒ Natural Indicators:

Some indicators are found in nature. Obtained from plants.

Example - litmus solution. It is a purple colour dye. It is obtained from lichen plants that belong to the division 'Thallophyta'.

• Here are some natural indicators with characteristic colour-

$\begin{array}{| c | c | c |}\cline{1-3} \bf Idicator & \bf Colour\ in& \bf Colour\ in\\ \cline{1-1} & \bf Acidic\ medium & \bf alkaline\ medium \\ \cline{1-3} \sf Litmus & Red & Blue \\ \cline{1-3} \sf Red\ cabbage(juice\ from\ leaves)& Red & Green\\ \cline{1-3} \sf Turneric \ juice& Yellow& Reddish\ brown\\ \cline{1-3} \sf Flowers\ of\ Hydrangea\ plant & Blue& Pink \\ \cline{1-3} \end{array}$

⇒ Synthetic Indicators:

The indicators that are made in the laboratory or industry. They are not natural. Some examples are - $\sf{\blue{Methylene\ blue}}$, $\sf{\red{Methyl\ red}}$, $\sf{\orange{methyl\ orange}}$.

• Here are some synthetic indicators with characteristic colour-

$\begin{array}{| c | c | c |c|}\cline{1-4} \bf Idicator & \bf Colour\ in& \bf Colour\ in & \bf Colour\ in\\ \cline{1-1} & \bf Acidic\ solution& \bf basic\ solution& \bf Neutral\ solution\\ \cline{1-4} \sf Phenolphthalein& Colourless& Pink& Colourless \\ \cline{1-4} \sf Methyl\ orange& Red & Yellow& Orange\\ \cline{1-4} \end{array}$

⇒ Olfactory Indicators:

The indicators changes the odour in acidic and basic medium.

Some indicators are Vanilla and onion.

⇒ Universal Indicators:

It gives different colours at various concentrations of Hydrogen ion in a solution.