Define Indicator in chemistry- class 10 notes

Define Indicator -Class 10 

Indicator is most important topic of NCERT  Acids bases salt  chapter 2  in Class 10.  Questions are frequently asked in the CBSE  board  and  ICSE Board exam from  definition of indicator  . 

“Chemistry  – Define Indicator  : class 10 notes “ will be very beneficial for the students who are engaged in the preparation of  upcoming board exam.

In this topic, the following terms will be illustrated.

Contents :

* 1. Definition of Indicator

* 2. Type of Indicator :  Natural Indicator ,  Synthetic Indicators ,  Olfactory Indicator , Universal Indicator

* 3. pH scale color chart , Importance of pH in our life

Definition of indicator :

• A  substance which is used to detect acidic or basic medium is called indicator.

• When indicator is kept in acidic or basic medium , its colour or smell is changed.

Types of indicators:

1. Natural Indicator:

• It occurs naturally. e.g  Litmus, Turmeric, Red cabbage etc.

Litmus:

• It is natural indicator whose neutral colour is purple.
• It is extracted from lichen .
• It is used in form of liquid as well as paper strip.
• It turns red in acidic medium and blue in basic medium.

 Turmeric:

• It is also neutral indicator.
• It is yellow in neutral condition.
• It remains same in acidic medium.
• It turns red in basic medium.

 Red cabbage:

• Its neutral colour is red.
• It remains red in acidic medium.
• It turns green in basic medium.

Other natural indicator are some flowers like Hydrangea, Petunia, Geranium etc

NATURAL INDICATOR
Indicator	Neutral Colour	Colour In acidic Medium	Colour In Basic  Medium
Litmus	Purple	Red	Blue
Turmeric	Yellow	Yellow	Red
Red cabbage	Red	Red	Green

 2. Synthetic Indicators:

• The indicators which are  prepared in laboratory  are called synthetic indicators.

Methyl orange:

Structure of Methyl orange

• Its neutral colour is orange.
• It turn red in acidic medium.
• It turns yellow in basic medium.

 Phenolphthalein:

Phenolphthalein

• It is colorless in  neutral state.
• It remains colorless in acidic medium.
• It turns pink  in basic medium

Synthetic Indicaror	Neutral Colour	Colour In acidic Medium	Colour  In Basic  Medium
Methyl orange	Orange	Red	Yellow
Phenolphthalein	Colourless	Colorless	Pink

 3. Olfactory Indicator:

• Those substances whose smell change in acidic or basic medium are called olfactory indicators.

• The term ‘ olfactory ‘ means ‘ relating to the sense of smell’  .
• Onion and vanilla extract are olfactory indicators.
• Characteristics smell of onion and vanilla are remain same in acidic medium .
• Characteristics smell of onion and vanilla can not be detected in basic medium.

 4. Universal Indicator:

• Those substance which is used to detect acidic and basic medium with strength of Hydrogen ions (pH ) is called universal indicator.

• Universal indicator is a mixture of many different indicators which gives different color at different pH value  of medium.

• The colour produced by universal indicator when mixed with given solution  is used to find  pH value of solution by matching the colour with the colour on pH colour chart.

ph scale color chart
Colour of solution	pH Value	Nature of medium
Dark red	0	Acidic Medium
Red	1
Red  (pink )	2
Orange red	3
Orange	4
Orange yellow	5
Greenish yellow	6
Green	7	Neutral Medium
Greenish blue	8	Basic Medium
Blue	9
Navy blue	10
Purple	11
Dark purple	12
Violet	13
Dark violet	14

Indicator list 

 

Importance of pH in Everyday Life

Our body works within the pH range of 7.0 to 7.8.  Living organisms can survive only in a narrow range of pH change.  When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

 

pH in our digestive system

* Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach.

* During indigestion the stomach produces too much acid and this causes pain and irritation.

* To get rid of this pain, we use bases called antacids.  These antacids neutralize the excess of acid .

* Milk of magnesia   Is often used for this purpose.  Chemical name of Milk of magnesia  is Magnesium hydroxide  Mg (OH)₂ .

 

pH change as the cause of tooth decay

* Tooth decay starts when the pH of the mouth is lower than 5.5.

* Tooth enamel, made up of calcium hydroxyapatite.  calcium hydroxyapatite is a crystalline form of calcium phosphate  which is the hardest substance In the body.

* Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining In the mouth after eating.

* It  is corroded when the pH in the mouth is below 5.5.

* The best way to prevent this is to clean the mouth after eating food.

* Using toothpastes, which are generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.

 

Self defence by animals and plants through chemical warfare

* Bee-sting leaves an acid which causes pain and Irritation.

* Use of a mild base like baking soda on the stung area gives relief.

* Stinging hair of nettle leaves inject methanol acid causing burning pain.

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