Acids, Bases and Salts
Science Class Seven
Summary: Quick Reading
(1) Substances that taste sour contain acid. Or substances that contain acid taste sour.
(2) The chemical nature of substances that contain acid is called acidic. For example tamarind, lemon, orange, hydrochloric acid, sulphuric acid, etc.
(3) Substances that taste bitter and feel soapy in touch contain base.
(4) The chemical nature of substances that contain base is call basic. For example baking soda, baking powder, soap, etc.
(5) All citrus foods contain acid. In other words substances that contain acid are sour in taste. Example tamarind, orange, lemon, vinegar, unripe mango, amla, etc.
(6) Acid found in citrus food are called natural acid. This means acid found in nature are known as natural acid.
(7) Acetic acid is found in vinegar, formic acid is found in ant’s sting, citric acid is found in citrus foods, such as lemon, orange, etc. lactic acid is found in curd, ascorbic acid found in amla and other many citrus fruits, tartaric acid found in tamarind, grapes, and unripe mango, etc.
(8) Base such as calcium hydroxide is found in lime water, ammonium hydroxide is found in window cleaner, sodium hydroxide and or potassium hydroxide is found in soap, magnesium hydroxide is found in milk of magnesia.
(9) The word acid came from the Latin word "Acere" which means acid.
(10) Substances which are used to test acid or base are called indicators or acid-base indicators. Example: litmus, China rose, turmeric, etc. These are naturally occurring indicators.
(11) Indicators show the presence of acid or base by changing colours.
(11) Litmus is the most commonly used indicator. Litmus is obtained from a plant called Lichens.
(12) Litmus solution is mauve in colour originally.
(13) Litmus solution turns red when added into acid.
(14) Litmus solution turns blue when added into base.
(15) Litmus paper comes in two colour blue and red.
(16) Blue litmus paper turns red when dipped in an acid or acidic solution.
(17) Red litmus paper turns blue when dipped in a base or a basic solution.
(18) Solution which is neither acidic nor basic is called a neutral solution for example distilled water.
(19) Litmus paper does not change its colour when dipped in a neutral solution.
(20) Turmeric is another indicator.
(21) The colour of turmeric solution or turmeric stain on a cloth or paper turns reddish brown with a base. This is the cause when soap is applied over the vegetable or curry stain on a cloth turns reddish brown.
(22) Turmeric paper or solution or stain does not change its colour with acid.
(23) China Rose is another natural indicator. Solution of China Rose petals can be prepared by keeping china rose petals in warm water for some time.
(24) The China rose solution is pink in colour originally.
(25) China Rose solution turns red (dark magenta) with acid and turns greenish with base.
(26) Phenolphthalein is another indicator which is used to test acidic and basic nature of the substances in laboratory.
(28) Phenolphthalein is a colourless liquid.
(29) Phenolphthalein gives pink colour with base and remains colourless with acid.
(30) Neutralisation is a process in which acid and base mixed together in a particular ratio to form salt and water. In this process acid and base neutralised each other.
Example: When Hydrochloric acid and Sodium Hydroxide are mixed together, water and common salt (Sodium chloride) are formed.
Hydrochloric acid (HCl) + Sodium Hydroxide (NaOH) ⇒ Sodium chloride (NaCl) + Water (H2O)
(31) In the process of neutralisation heat is also evolved along with salt and water. Since heat is evolved in the process of neutralisation, it is called exothermic reaction also.
(32) Reaction in which heat is evolved is called an Exothermic Reaction.
(33) The process of neutralisation is known as neutralisation reaction also.
(34) Indigestion: When a person eats more than usual, the stomach starts forming more acid to digest the extra food. In this situation because of formation of excessive acid, the person who overeaten feels burning sensation and pain in stomach. This situation is called indigestion. Indigestion is a painful situation. To get relief from indigestion, doctors prescribe antacid tablets or solution.
An antacid contains base which neutralises the extra acid produced in the stomach and the sick person gets relief.
To get relief from indigestion, Digene, Milk of magnesia, etc. are prescribed. These tablets or solution contains base. Antacids are available in the market in the form of tables and syrup.
(35) Ant bite: While biting ant injects formic acid in the skin of victim. Because of injecting of forming acid, the victim feels pain at the place of biting.
To get relief from the pain of ant bite, moist baking soda or calamine solution is rubbed over the place of biting. Baking soda and calamine solution are base which neutralises the acid injected during the ant bite and victim gets rid of pain.
(36) Soil treatment : Because of excessive use of fertilisers many times soil either turns acidic or basic. This reduce the fertility of soil resulted in the form of less yield or no yield.
To neutralise the acidity soil is treated with base like slaked lime (Calcium Hydroxide) or quick lime (Calcium oxide). The adding of base to the soil neutralises acidic nature of soil and it becomes fertile again.
In the case of excessive basic nature of soil, it is treated with organic matter by adding it to the soil. Organic matter neutralises the basic nature of the soil.
(37) Factory Waste: Factory waste contains acid. Thus if it is flushed in the water without any treatment, it will increase the acidity of water which will kill the aquatic animals and other organism found in water.
Thus, before flushing the factory waste in water it is treated with basic substances in order to neutralise it.
(38) Acid Rain: In factories and vehicles because of burning of fuel carbon dioxide, sulphur dioxide, and nitrogen dioxide, etc. are expelled out and get mixed with air. These gases form carbonic acid, sulphuric acid and nitric acid respectively when dissolve in water. While raining these gases get dissolved with rain drop and fall on the earth along with rain drops. This is called acid rain. Acid rain is dangerous for buildings, monuments, animals and plants.
(39) Preparation of Lime Water: Lime water is prepared by adding quick lime into water. By adding of quick lime in water calcium hydroxide is formed along with heat. This preparation of lime water is an exothermic reaction because heat is evolved in it.
(40) Making of turmeric paper: Turmeric paper can be made by applying of turmeric paste on paper strips or a sheet of paper.
(41) The full form of DNA is deoxyribonucleic acid. DNA is found in our body which decides the every feature of an individual body such as looks, colour, height, etc. Every person has unique DNA.
(42) Proteins are made of amino acids. Proteins build our cells and consequently our body.
(43) Fats contain fatty acids. Fat is the food storage in our body. Excessive presence fats in our body cause obesity.
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