Be reactive

Q What is an indicator?A: A substance that changes colour depending upon whether it is acidic, neutral or alkaline

solution.

Q What is litmus?A: Litmus is an indicator made from lichen plant which turns red in acid and blue in alkaline

solutions.

Q What is universal indicator?A: Universal indicator is a mixture of four different indicators. It has range of colours like rainbow.

It shows how strong or weak the acid or alkali is. It comes in the form of paper or a solution.

Q Name some natural indicators.

Plant Original colour

Colour in acid

Colour in alkali

Red cabbage purple pink green

Hibiscus dark red red green

Rose pink pink green

Red spinach red pink yellow

Geranium red orange yellow

periwinkle yellow pink yellow

Coleus brown pink yellow

Q What is pH value?A: The degree of acidity or alkalinity of a substance can be expressed by its pH value. Acids have pH value of less than 7. Alkalis have pH value of more than 7. Neutral solutions have a pH of 7.

Q Make a table to show colour of indicator, their strength, pH value and give example.

pH value Colour of universal indicator

Strength Example

0 Red Strong acid1 Red Strong acid Hydrochloric acid2 Red Strong acid vinegar3 Red Strong acid Lemon juice, grape4 Pink Weak acid Acid rain5 Orange Weak acid Tap water6 Yellow Weak acid Rain water7 Green Neutral Pure water8 Turquoise Weak alkali Sea water9 Blue Weak alkali toothpaste10 Dark blue Weak alkali Milk of magnesia11 Violet Strong alkali ammonia12 Violet Strong alkali bleach13 Violet Strong alkali Lime water14 Violet Strong alkali Sodium hydroxide

Q What is pH Meter and pH Sensor? How it is used?A: pH meter and pH Sensor are used to get accurate pH values. In pH Meter, the electrode is simply dipped into a

solution and pH value is read from the meter. A pH sensor can also be connected to a computer and the pH values are read from the screen.

Q Give pH value of different parts in our body.A: The human body contains lots of liquids which have different pH value. Ex Liquid in stomach have 1.5 pH,

because they contain hydrochloric acid. Saliva has 6.2, blood has 6.5, intestinal juice has 8.4 and our skin has 5.5 pH values.

Q How is pH value of soil important for farmers?A: Different plant grows in different soil. For apple trees pH value should be 5 to 6 (slightly acidic) and for mint

plants 7 to 8 (neutral or slightly alkaline). If soil is too acidic then farmers can add lime (an alkali) to neutralise the soil.