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Acids Bases and Salts - Class 10 Science Textbook Solutions

 Acids Bases and Salts 
1. Two solutions A and B have pH values of 5 and 8 respectively. Which solution will be basic in nature?
Solution B.
2. If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done?
The hand should be washed immediately with plenty of water and a paste of sodium hydrogen carbonate (a base) must be applied to neutralise the acid.
3. If someone is suffering from the problem of acidity after overeating; which of the following would you suggest as a remedy?
Lemon juice, Baking soda solution or Vinegar.
Baking soda solution because it is basic in nature and hence neutralises the excess acid present in the stomach.
4. Arrange the following in the increasing order of acidic strength. Acetic acid, water and hydrochloric acid

Water < acetic acid < hydrochloric acid.
5. Why does tooth decay start when the pH of mouth is lower than 5.5 ?
: Tooth starts decaying when the pH of our mouth is lower than 5.5. This is because below this pH value, the medium of the mouth becomes more acidic due to which tooth enamel corrodes at a faster rate.
6. Two solutions X and Y have pH values of 3.0 and 9.5 respectively. Which of these will turn litmus solution from blue to red and which will turn phenolphthalein from colourless to pink?
X will turn blue litmus to red because it is acidic in nature having pH value less than 7. Y will turn phenolphthalein from colourless to pink because it is basic in nature having pH value. greater than 7.
7. Why aqueous ammonia solution considered a base although ammonia does not contain hydroxyl (OH-) ion ?
Ammonia dissolves in water as follows:

The hydroxyl ions produced in the solution are responsible for basic character of ammonia.

8. A knife, which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution. The colour of the solution changes to red, what is the nature of the fruit ?
The fruit is acidic as it turns blue litmus solution to red.

9. Explain why an aqueous solution of ammonium chloride is acidic in nature.
Ammonium chloride (NH4Cl) is the salt of a strong acid, hydrochloric acid (HCl), and a weak base ammonium hydroxide (NH4OH), so an aqueous solution of ammonium chloride is acidic in nature.

10. What are the products formed when an acid reacts with a base ?
acid reacts with a base to form salt and water.

11. Fresh milk has a pH of 6. When it changes into curd (yogurt), will its pH value increase or decrease ? Why?
When milk changes into curd (yogurt), its pH value decreases. This is because during curd formation, lactic acid is produced which makes it acidic.

12. A white chemical compound becomes hard on mixing proper quantity of water. It is also used in surgery to maintain joints in a fixed position. Name the chemical compound
Plaster of Paris (calcium sulphate hemihydrate).

13. Which one of these has a higher concentration of H+ ions ?

Answer: 1 M HCl has a higher concentration of H+ ions because it is a stronger’ acid than CH3COOH.

14. In addition to sodium hydrogencarbonate, baking powder contains a substance ‘X’. Name the substance ‘X’.
Tartaric acid.

15. What is the commerClal name of calcium sulphate hemihydrate ?
Plaster of Paris.

16. Name the substance obtained by the action of chlorine on dry slaked lime.
Bleaching powder.

17. Write two methods of preparation of baking soda along with the chemical equation.
Preparation Method:

18. Why does the milkiness disappear on passing excess of carbon dioxide to lime water ?
When carbon dioxide is passed in excess, calcium carbonate (which appears milky) gets converted into calcium hydrogencarbonate which is soluble. Hence, the milkiness disappears.

19. An aqueous solution turns red litmus solution blue. Excess addition of which solution would reverse the change ammonium hydroxide solution or hydrochloric acid?
Hydrochloric acid because adding excess acid to the base would turn blue litmus solution red.

20. Plaster of Paris should be stored in moisture proof container. Explain why?
Plaster of Paris reacts with moisture and gets hardened due to formation of gypsum so it is stored in moisture proof container.

21. Why is the electrolysis of a concentrated solution of sodium chloride known as chlor-alkali process?
It is because of the products formed : chlor for chlorine and alkali for sodium hydroxide.

22. Write the modern definition of acid and base. Give one example of each.

acid : Those substances which give hydrogen ions (H+) or hydronium ions (H3 O+) on dissoClation in aqueous solution are called acids, e.g. HCl (aq) ⇌ H+ + C1–
Base : Those substances which give hydroxide ions (OH–) on dissoClation or ionisation in aqueous solution are called bases, e.g. NaOH (aq) ⇌ Na+ + OH–

23. Explain the method of preparation of bleaching powder.
Bleaching powder (CalCl2) is prepared by action of chlorine on dry slaked lime.

24. What is pH value ? Describe its importance in our daily life:
pH Scale : It is a scale used for measuring hydrogen ion concentration. The p in pH stands for potenz which means power in German.
It has values ranging from 0 (very acidic) to 14 (very alkaline). Thus, pH is a number which indicates the acidic or basic nature of a solution.
Importance in everyday life :
(1) Plants and Animals are pH sensitive : Living or ganisms can survive only in a narrow range of pH change, our body works normally within a pH range of 7 to 7.8.
(2) pH in Our Digestive System : HCl present in the stomach helps is the digestion of food. During indigestion the stomach produces too much acid, it couses pain and irritation.

Acids Bases and Salts Extra Questions Short Answer Type

1. What is an olfactory indicator ? Name two such indicators.
Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extract are olfactory indicators.

2. Name the acid present in the following:
(i) Tomato
(ii) Vinegar
(iii) Tamarind

(i) Cltric acid
(ii) Acetic acid
(iii) Tartaric acid.

3. List in tabular form two differences between an acid and a base based on their chemical properties.

 4. What happens when a cold and concentrated solution of sodium chloride reacts with ammonia and carbon dioxide ? Write the equation of the reaction which takes place.
When a cold and concentrated solution of sodium chloride reacts with ammonia and carbon dioxide, sodium hydrogencarbonate (baking soda) and ammonium chloride is formed.

5. Name the gas evolved when dilute HCl reacts with sodium hydrogen carbonate. How is it recognised ?
Co2 gas is evolved. The reaction is as follows:

When the produced gas is passed through lime water, lime water turns milky which confirms that the evolved gas is CO2.

6. The pH of soil A is 7.5 while that of soil B is 4.5. Which of the two soils should be treated with powdered chalk to adjust its pH and why?
Answer: Soil B having pH 4.5 should be treated with powdered chalk to adjust its pH. Soil B is too acidic. Its acidity can be reduced by adding powdered chalk (CaCO3), which is a base.

7. Write down the molecular formula and chemical name of Baking soda. Give the chemical equation of its preparation.
Baking Soda : Its chemical name is Sodium Hydrogen Carbonate (or Sodium Bicar bonate).
Its molecular formula is NaHCO3.
Preparation :

 8. The conditions preferred by some plants are shown in the table below:

(a) Which plants grow well over the largest range of pH values ?
(b) Which plant can grow in the most acidic soil ?
(c) Which plant can grow in the basic soil only?
(d) What is the pH range for onion to grow well ?

(a) Black currant and strawberry
(b) Potato (4.5 – 6.0)
(c) Mint (7.0 – 8.0)
(d) 6.0 – 7.0

(i) Name the products formed when sodium hydrogencarbonate is heated.
(ii) Write the chemical equation for the reaction involved in it.

(i) On heating sodium hydrogencarbonate (NaHCO3), it decomposes to form sodium carbonate (Na2.CO3), water (H2O) and carbon dioxide (CO2).

10. Name the acid present in an ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.
The acid present in an ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. To get relief, one should apply any available basic salt, e.g., baking soda (NaHCO3) on it.

11. What happens when nitric acid is added to an eggshell ?
Eggshells contain calcium carbonate. When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as

 12. When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction and also write a test to detect the gas formed.
When zinc reacts with dilute solution of strong acid, it forms salt and hydrogen gas is evolved.

When a burning splinter is brought near the mouth of the test tube, the gas burns with a pop sound.

13. What will be the action of the following substances on litmus paper ? Dry HCl gas, Moistened NH, gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.

14. A student prepared solutions of
(i) an acid and
(ii) a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two ?
In the absence of litmus paper, any indicator like methyl orange, phenolphthalein can be used. Natural indicator like turmeric can also be used.

15. Which acid is produced in our stomach ? What happens if there is an excess of acid in the stomach ? How can its effect be cured ?
Hydrochloric acid is produced in our stomach. The excess acid in the stomach causes indigestion which produces pain and irritation. This effect can be cured by using antacids. Antacids (a group of mild bases) react with excess acid in the stomach and neutralise it.

16.To the three solutions listed below, a few drops of phenolphthalein and blue litmus were added separately. SpeClfy the colour change in each case, if any:





17. A salt X when dissolved in distilled water gives a clear solution which turns red litmus blue. Explain this phenomenon.
Basic solutions turn red litmus paper blue. The salt of a weak acid and a strong base gives a basic solution. SO, the given salt X is the salt of a weak acid and a strong base. . Example : When sodium carbonate is dissolved in water, it gets hydrolysed to some extent and forms sodium hydroxide and carbonic acid.

Being a strong base, sodium hydroxide is fully ionised and gives a large amount of hydroxide ions (OH–). Carbonic acid is a weak acid which is only slightly ionised and hence, gives a small amount of hydrogen ions (H+). The H+ ions produced by carbonic acid neutralises only a small amount of OH-ions produced by sodium hydroxide and the rest amount of OH–ions are present in the solution. Hence, the Na2 CO3 solution is basic in nature. It turns red litmus blue.

18.With the help of a chemical equation, explain how a soda-acid fire extinguisher helps in putting out a fire.
Soda-acid fire extinguisher contaisn sodium bicarbonate and sulphuric acid, which are in separate containers in them. When knob of the fire extinguisher is pressed, then sulphuric acid mixes with sodium bicarbonate solution and produces a lot of CO, gas, which forms a blanket over the fire and cuts it off from the supply of the air to the burning substance and the fire stops.

 19. Give a method of preparation of Plaster of Paris and also give one use.
The compound prepared from gypsum on heating it at 100°C, is known as Plaster of Paris. Its chemical formula is CaSO4.12 H2O. Hence, its chemical name is calcium sulphate hemihydrate. The chemical equation for its preparation is as follows :

Plaster of Paris is used in hospitals mainly as plaster for supporting fractured bones in the right position. In dentistry, it is used for making casts.

20. What is meant by water of crystallisation ? Explain that the crystalline salts contains water of crystallisation.
Water of crystallisation is a fixed number of water molecules present in one formula unit of a salt. One formula unit of copper sulphate contains five water molecules (5H2O). The water molecules which form part of the structure of a crystal are called water of crystallisation. When hydrated salts are heated strongly, they lose their water of crystallisation.
On strong heating, blue copper sulphate crystals turn white (due to the loss of water of crystallisation).

21.(i) Write the formula and chemical name of bleaching powder.
(ii) Write the chemical equation to represent the action of atmospheric CO2 gas on bleaching powder when left exposed in open.
(iii) State for what purpose is bleaching powder used in water treatment plants.

(i) Chemical formula : CaOCl2
Chemical name : calcium oxychloride

(iii) Bleaching powder is used in water treatment plants for disinfecting drinking water to make it free of germs.

22. How would you distinguish between baking powder and washing soda by heating?
The chemical formula of baking powder is sodium hydrogencarbonate (NaHCO3); whereas; that of washing soda is sodium carbonate (Na2 CO3.10H2O).
Sodium hydrogencarbonate on heating gives CO2 gas which will turn lime water milky whereas no such gas is obtained from sodium carbonate.


23. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and
Baking powder (NaHCO3), salt A is commonly used in bakery products. On heating, it forms sodium carbonate (Na2CO3), B and CO2 gas, C is evolved. When CO2 gas is passed through lime water it forms calcium carbonate (CaCO3), which is slightly soluble in water making it milky.

 24. What are strong and weak acids ? In the following list of acids, separate strong acids from weak acids; Hydrochloric acid, Cltric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
In aqueous solutions, strong acids ionise completely and provide high concentration of hydronium ions. On the other hand, weak acids are partially ionised and an aqueous solution of same molar concentration provides a much smaller concentration of H3O+ ions.
Strong acids-Hydrochloric acid, sulphuric acid, nitric acid.
Weak acids-Cltric acid, acetic acid, formic acid.

25. What happens when dilute hydrochloric acid is added to the following and write balanced chemical equations :
(i) Bleaching powder
(ii) Zinc granules
(iii) Baking soda

26. Give suitable reason for the following statements :
(i) We feel burning sensation in the stomach when we overeat.
(ii) The crystals of washing soda change to white powder on exposure to air.
(iii) An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.

(i) When we overeat excess of acids is produced in the stomach which causes burning sensation.
(ii) Washing soda is sodium carbonate decahydrate which when exposed to air loses 10 molecules of water and changes to white powder.
(iii) Sodium chloride is a salt of strong acid HCl and strong base NaOH, so it is neutral.. Sodium carbonate is a salt of weak acid H2CO3 and strong base NaOH, so it is basic.

(i) How is plaster of Paris chemically different from gypsum ? How can they be interconverted ? Write two uses of Plaster of Paris.
(ii) What is the effect of temperature on plaster of Paris?

(i) Plaster of Paris is chemically CaSO4.1/2H2O, but gypsum is CaSO4.2H2O. On heating gypsum (CasO4.2H2O) at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4 . 12H2O).
On mixing with water, plaster of Paris changes to gypsum once again leaving a hard solid mass.
Uses :
(a) It is used for making ceiling designs.
(b) It is used for joining the fractured bones.
(ii) On heating plaster of Paris, it loses water molecules and becomes calcium sulphate.

28. Write chemical equation for the preparation of Washing soda and also give its one use.
Answer: Sodium Carbonate is a white crystalline solid. It is called Washing soda. Sodium Carbonate can be obtained by heating baking soda.


Use: It is used in glass, soap and paper industries.

Acids Bases and Salts Extra Questions Long Answer Type

1. (i) In the following schematic diagram for the preparation of hydrogen gas as shown in figure, what would happen if following changes are made ?
(a) In place of zinc granules, same amount of zinc dust is taken in the test tube. (b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
(c) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
(ii) How do metal carbonates and metal hydrogencarbonates react with acids ?

(i) (a) Hydrogen gas will evolve with greater speed.
(b) Almost same amount of gas is evolved.
(c) If sodium hydroxide is taken, hydrogen gas will be evolved.

ii) All metal carbonaes and hydrogencarbonates react with acids to form a corresponding salt, carbon dioxide and water.
Metal carbonate + acid → Salt + Carbonate dioxide + Water
Metal hydrogencarbonate + acid → Salt + Carbon dioxide + Water
For example, sodium carbonate reacts with dilute hydrochloric acid as follows:

2. A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disintifecting drinking water. Identify X, Y, G and Z. [NCERT Exemplar]
The gas evolved at anode during electrolysis of brine is chlorine (G).
When chlorine gas is passed through dry Ca(OH)2 (Y) produces bleaching powder (Z) used for disintifecting drinking water.

Since Y and Z are calcium salts, therefore X is also a calcium salt and is calcium carbonate :

3. A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and state why does it show such a behaviour. Give the reaction involved.
The substance which is used for making different shapes is Plaster of Paris. Its chemical
name is calcium sulphate hemihydrate (CaSO4 – 12H2O). The two formula unit of Caso share one molecule of water. As a result, it is soft.
When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.

4. Write the formulae of the salts given below:
Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
Identify the acids and bases from which the above salts may be obtained. How many families can you identify among these salts ?

The formulae of the given salts and the acids and bases from which these salts may be obtained are given in the following table :

hat Happens When ?

1. Write only the chemical reaction of the following:
(i) Effect of temperature on sodium bicarbonate.
(ii) Sodium bicarbonate with hydrochloric acid.

How to obtain ?

1. Write only the chemical reactions of the following:
(i) Sodium bicarbonate from sodium chloride
(ii) Plaster of Paris from gypsum

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