acids bases and salts class 7 easy study material

ACIDS, BASES AND SALTS CHAPTER-5 GRADE 7-CHEMISTRY

acids bases and salts class 7 notes

In our daily life, we are using many vegetables and fruits which are sour. Have you ever wondered, why these are sour to taste?

Lemon, orange, vinegar, curd-like that many sour things we include in our diet. At the same time, some food items are sweet, bitter, and salty. Let's learn the chemistry behind these.

ACIDS

Substances that are sour to taste contain acids in it. Those substances are acidic in nature. The word acid itself means sour. Fruits and vegetables contain natural acids.

citrus fruits

NATURAL ACIDS-acids which occur in nature. It is also called organic acids.

Acetic acid	vinegar
Formic acid	ant's sting
Citric acid	citrus fruits like lemon, orange, etc.
Lactic acid	curd, buttermilk
Oxalic acid	spinach, tomato
Ascorbic acid   (vitamin C)	citrus fruits, gooseberry
Tartaric acid	tamarind, grapes, unripe mango

MINERAL ACIDS- acids that are made from inorganic minerals. Hence it is also called inorganic acids. Examples are given in the table below.

Hydrochloric acid	HCl
Sulphuric acid	H2SO4
Nitric acid	HNO3
Phosphoric acid	H3PO4

Sulphuric acid is called the King of chemicals.

BASES

There are certain substances that are bitter to taste and soapy to touch. Such substances are called bases. The nature of such substances is basic.

Examples: baking soda, Calcium hydroxide(lime water), Sodium hydroxide, Potassium hydroxide, Magnesium hydroxide

baking soda

INDICATORS

Substances that are used to test whether a given sample is acidic or basic are called indicators.

Indicators can show different colors with an acidic or a basic substance.

Indicators can be of two types:

• Natural indicators- turmeric, litmus solution or litmus paper, china rose petals, red cabbage juice
• Synthetic indicators- phenolphthalein, methyl orange

LITMUS

It is a commonly used indicator. Litmus is extracted from lichens. In distilled water, it has a purple color. It turns red when added to acids and it turns blue when added to bases.

Litmus solution or litmus paper is available for testing. Commonly we are using red litmus paper and blue litmus paper.

On dipping a blue litmus paper in acid, it turns red.

On dipping a red litmus paper in acid, it remains red(no color change).

On dipping a red litmus paper in the base, it turns blue.

On dipping a blue litmus paper in the base, it remains blue(no color change).

lichens

Neutral solutions

Substances that are neither acidic nor basic are called a neutral solution. They do not show any color change with red or blue litmus papers.

Example- distilled water, salt solution, sugar solution

TURMERIC 

turmeric

Turmeric indicator can be made at home by applying a paste of turmeric on a piece of white paper and drying it. When you apply a drop of soap solution on it, it turns red. This indicates that soap is basic.

with acid- yellow color

with base- red color

CHINA ROSE 

China rose (hibiscus)

For making china rose indicator, take some china rose petals and mix it with warm water and keep it aside for some time. The colored solution obtained can be used as an indicator.

With acid- magenta (dark pink)

With base- green

SYNTHETIC INDICATORS

Phenolphthalein- Color change

With acid - colorless

With base - pink

Methyl orange- color change

With acid- red

With base- yellow

NEUTRALISATION

The reaction between an acid and a base to obtain salt and water is called neutralization.

Acid + Base → salt + water

Example: On adding Hydrochloric acid to Sodium hydroxide, Sodium chloride and water are formed. In this Sodium chloride is the salt formed. Heat is also produced during this reaction.

Hydrochloric acid + Sodium hydroxide →Sodium chloride + water

HCl + NaOH →NaCl + H2O

NEUTRALISATION IN EVERYDAY LIFE

                                1. INDIGESTION

antacid-gelucil tab

When we have indigestion problems, we usually take this kind of medicine. The hydrochloric acid present in our stomach helps indigestion. But when there is more amount of this, it causes acidity. 

To reduce acidity, we are taking mild bases like milk of magnesia which contains Magnesium hydroxide. These bases are called antacids and it can neutralize the effect of excess acid and relieve stomach pain.

2. ANT BITE

ant 

When an ant bites our body, it injects formic acid and it causes irritation and pain. 

On rubbing moist baking soda (sodium hydrogen carbonate) or calamine lotion (zinc carbonate), the effect of an acid can be neutralized.

3. SOIL TREATMENT

soil treatment

When the soil is too acidic, we must add bases like quick lime or slaked lime. Organic matter like leaf waste and decayed vegetables are added when the soil is more basic. This way we can neutralize the soil for the better growth of the plant. 

4.FACTORY WASTE

factory waste

The factory wastes are neutralized with bases if they contain more acid in it. If it is disposed directly to the water bodies, it will affect the aquatic life. There should be proper pollution checks in this area to save our natural resources.