Basic Science Solutions for Class 7 Science Chapter 2 Acids, Bases And Salts are provided here with simple step-by-step explanations. These solutions for Acids, Bases And Salts are extremely popular among Class 7 students for Science Acids, Bases And Salts Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 7 Science Chapter 2 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 7 Science are prepared by experts and are 100% accurate.

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Acidic: Tomato juice, lemon juice and vinegar (they turn blue litmus red)
Alkaline: Toothpaste and soap solution (they turn red litmus blue)

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Sulphuric acid (H2SO4), nitric acid (HNO3) and phosphoric acid (H3PO4) are examples of mineral (or inorganic) acids.

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Acids are substances that taste sour and corrode metals. They react with bases and get neutralised to form salt and water. An acid furnishes H+ ions when dissolved in water.

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Bases are substances that taste bitter and are slippery to the touch. They neutralise acids and form salt and water on reaction with acids. A base furnishes OH ions when dissolved in water.

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An alkali is a base that dissolves in water. When a base dissolves in water, it furnishes OH ions. Examples: Sodium hydroxide and calcium hydroxide.

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A substance that has neither acidic nor alkaline character is termed chemically neutral or neutral substance.

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Fossil fuels like coal and natural gas, apart from carbon, contain impurities like sulphur and nitrogen. On burning the fossil fuels, these elements react with oxygen in air to form acidic oxides like sulphur dioxide, sulphur trioxide, nitric oxide and nitrogen dioxide. They are formed in accordance with following reactions:

S + O2 → SO2    (formation of sulphur dioxide)

2SO2 + O2 → 2SO3    (formation of sulphur trioxide)

N2 + O2 → 2NO      (formation of nitric oxide)

2NO2 + O2 → 2NO2     (formation of nitrogen dioxide)

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Following are the characteristics of bases:

1. They have a bitter taste.
2. They are slippery to touch (like soap).
3. They furnish OH ions when dissolved in water. (Soluble bases are called alkalis.)
4. They turn red litmus blue.

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Properties of Acids:

• Acids are  corrosive in nature. They damage the surface of metals when they make contact with them. Sour food items are not kept in metal containers because, such food items react with metal container and form metal salts and hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2
H2SO4 + Fe → FeSO4 + H2
• When an acid is added to water, heat is generated. Almost all acids are readily soluble in water.
• Acids turn blue litmus red and show no effect on phenolphthalein and turmeric juice.
• Acids are sour in taste.
• Acids undergo neutralisation reaction i.e., they react with bases and get neutralised to form salt and water.
• Acids react with bicarbonates and carbonates to cause effervescence, releasing CO2 gas.

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Carbonate salts contain a metal ion and a CO32- (carbonate)ion. Bicarbonates contain a metal ion with a hydrogen carbonate ion, i.e., HCO3-. These carbonates and bicarbonates react with acids to form a metal salt and carbon dioxide. This release of CO2 causes effervescence in the reaction mixture.

2K2CO3 + 2HCl → 2KCl + H2O + CO2

A simple activity at home can demonstrate how an acid causes effervescence on reaction with a carbonate or a bicarbonate.
Take some baking soda powder in a transparent glass jar. Drop a few drops of vinegar or lemon juice on the powder in jar. Both vinegar and lemon juice are acidic in nature and contain acetic acid and citric acid, respectively. When acid drops on baking soda, which has sodium bicarbonate (NaHCO3) as its major constituent, bubbles are observed. These bubbles are formed due to the release of CO2 formed during the reaction. Now, to check whether only acid causes such an effect, you can drop a few drops of water on unreacted baking soda and can observe that there is no reaction. This activity demonstrates the effect of acids on carbonates and bicarbonates.

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When rainwater in clouds get mixed with sulphur dioxide and oxygen present in atmosphere, this mixture (i.e., sulphuric acid) is called acid rain.

It is mainly due to burning of coal, which contains sulphur as impurity and emits sulphur dioxide on burning. This sulphur dioxide in the atmosphere reacts with oxygen to form sulphur trioxide; it then reacts with the water in the clouds to form sulphuric acid.


S + O2 → SO2
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4

Harmful Effects of Acid Rain:
• It damages metal structures like bridges, windows, door frames, railings, buildings and monuments made up of marble and cement.
• It increases the acidity of water bodies like ponds, lakes and oceans causing great damage to aquatic life.
• It increases the acidity of soil and decreases its fertility.

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Uses of Bases:

(a) Lime or calcium hydroxide [Ca(OH)2] is used for whitewashing.
(b) NaOH and KOH are used in the manufacturing of soaps and detergents. Sodium hydroxide is sometimes used to clear drain blockages.
(c) Ammonia (NH3) is used in the manufacturing of fertiliser like ammonium nitrate (NH4NO3) and ammonium sulphate (NH4)2SO4.
(d) Magnesium hydroxide [Mg(OH)2] (milk of magnesia) is used in antacids (a medicine that neutralises hyperacidity in our body).
(e) Oxides of iron, copper, chromium and cobalt are colourful and are used in manufacturing coloured glasses.

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1. The sour things we eat contain acids.
2. Ammonium hydroxide is an alkali.
3. An acid is neutralised by a base.
4. An antacid generally contains a base.
5.

Indicator Colour
  Acid Base
Litmus Red Blue
Phenolphthalein Colourless Red
Turmeric juice Yellow Reddish-brown
Red cabbage juice Red Green
China rose juice Red Green

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(b) Oxides of nonmetals dissolve in water.
Acids are formed when oxides of non-metals dissolve in water.
Example: CO2 + H2O → H2CO3

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(d) sodium hydroxide
Acids are neutralised when they react with bases. Sodium hydroxide (NaOH) is a strong base that neutralises hydrochloric acid (HCl).

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(b) alkaline
A soap solution furnishes OH ions in water. Therefore, it is alkaline.

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A B
(a) Hydrochloric acid (iv) As bathroom acid
(b) Ascorbic acid (v) Vitamin C
(c) Sulphuric acid (i) In storage batteries
(d) Lactic acid (ii) Found in Yoghurt
(e) Acetic acid (iii) In making vinegar

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A B
(a) Sodium iodate (v) A supplement to common salt
(b) Calcium sulphate (iii) Present in plaster of Paris
(c) Bleaching powder (iv) A disinfectant
(d) Ammonium sulphate (ii) Used as a fertiliser
(e) Sodium benzoate (i) A food preservative

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1. Yes. Most salts are neutral.
2. Yes. Soluble bases are called alkalis.
3. No. Calcium chloride, on heating, loses water of hydration and may undergo dissociation at very high temperatures to form calcium metal and chlorine gas.
4. Yes. Lemon juice will give carbon dioxide with marble also.
5. Yes. Sulphur when burnt in air produces acetic acid.



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(d) salt and water
Reaction of an acid with a base is called a neutralisation reaction. In this reaction, salt, containing ions from reacting acid and base, is formed with water as a by-product.



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