Acids, Bases, and Salts: Indicators

• Acids, bases, and salts are vital chemical compounds.
• Examples of them being used include stomach acid (hydrochloric acid) for food digestion, baking soda (sodium hydrogen carbonate) in baking bread, and common salt (sodium chloride) as a cooking ingredient.
• Indicators are chemicals that show if a substance is an acid or a base by changing color.
• Litmus, China rose, and turmeric are natural indicators.

Indicators for Testing Acids and Bases

• An indicator is a dye that changes color in the presence of an acid or a base.
• Indicators reveal whether a tested substance is acidic or basic through color change.
• Acid-base indicators can be natural or synthetic.

Litmus

• Litmus, a natural dye from plants called lichens, is a common lab indicator.
• Litmus turns red in acidic solutions and blue in basic solutions.
• Blue litmus paper turns red when an acid is added.
• Red litmus paper turns blue when a base is added.

China Rose Indicator

• China rose, also known as Gudhal in Hindi, is a natural indicator.
• China rose indicator is a light pink coloured solution extracted from the red flowers of China rose plant with water.
• China rose indicator turns magenta (deep pink) when an acid is added.
• China rose indicator turns green when a base is added.
• Baking soda is a base because a drop of its solution turns China rose indicator green.

Turmeric as Indicator

• Turmeric is a natural indicator.
• Turmeric is a bright yellow powder obtained from a plant, called haldi in Hindi, is a yellow dye.
• Turmeric turns red in basic solutions and is often used as turmeric paper indicator.

Activity 2: Turmeric Paper Preparation

• Take a spoonful of turmeric powder
• Mix with a little water to make a paste
• Deposit the turmeric paste on a blotting paper (or filter paper) and dry it.
• Cut strips to create turmeric paper

Turmeric Paper

• Turmeric paper is yellow in color.
• Turmeric paper remains yellow in acid solutions.
• Bases will turn the yellow turmeric paper to red.

Phenolphthalein Indicator

• Phenolphthalein is a synthetic indicator.
• Phenolphthalein indicator is colorless in acidic solutions.
• Phenolphthalein indicator gives a pink color in basic solutions.
• Phenolphthalein indicator will change from pink to colorless when added in the solution of an acid in the solution of a base.
• In neutralization, a base cancels the effect of an acid seen with phenolphthalein.

Acids

• Lemons have a sour taste due to the acid within them.
• The sour taste of lemons is due to citric acid.
• Raw mangoes, grapes, lemon juice, curd, sour milk, vinegar, and tamarind get their sour taste from the acids these materials contain.
• Acids in plant and animal materials are called organic acids.

Organic Acids

• Organic acids are naturally occurring acids and are not harmful to consume.
• Formic acid is in insect stings.
• Acetic acid is found in vinegar.
• Lactic acid is in curd.
• Citric acid is in citrus fruits.
• Tartaric acid is in tamarind.
• Oxalic acid is present in spinach.

Mineral Acids

• Mineral acids are acids prepared from minerals.
• Mineral acids are also known as laboratory acides.