NIOS Class 10 Science and Technology Chapter 8 Acids, Bases and Salts

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NIOS Class 10 Science and Technology Chapter 8 Acids, Bases and Salts

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Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 10 Science and Technology Chapter 8 Acids, Bases and Salts, NIOS Secondary Course Science and Technology Solutions for All Chapters, You can practice these here.

Acids, Bases and Salts

Chapter: 8


1. Put the following substances in an acid or base bottle.

(a) Milk of magnesia.

Ans: Bottle.

(b) Gastric juice in humans.

Ans: Acidic.

(c) Soft drinks.

Ans: Acidic

(d) lime water.

Ans: Bottle.

(e) Vinegar.

Ans: Acidic.

(f) Soap.

Ans: Bottle.

2. What will happen if you add a drop of the following on a cut unripe apple, curd, caustic soda solution and soap solution.

(i) Phenolphthalein.

Ans: Phenolphthalein: Colourless on unripe apple and pink in solutions of caustic soda and soap.

(ii) Litmus.

Ans: Litmus: Red on unripe apple and curd, and blue in solutions of caustic soda and soap solution. 


1. Name the substances in which the following acids are present: 

(a) Ethanoic acid.

Ans: Vinegar.

(b) Tartaric acid.

Ans: Tamarind.  

2. Which of these acids would be partially dissociated in their aqueous solution?

(a) HBr. 

(b) HCN.

(c) HNO3.

(d) C2H5COOH.

Ans: (b) and (d). 

3. An acid reacts with a substance X with liberation of a gas which burns with a ‘pop’ sound when a burning match stick is brought near it. What is the nature of X? 

Ans: Vinegar.

4. An acid reacts with a substance Z with the liberation of CO2 gas. What can be the nature of Z? 

(a) CaO.

(b) SO2. 

Ans: It may be either a metal carbonate or hydrogen carbonate.

5. Which of the following oxides will react with a base?

Ans: SO2.


1. Why does the colour of dry blue litmus paper remain unchanged even when it is brought in contact with HCl gas?

Ans: It is because HCl gas does not contain H+(aq) ions and is non acidic.

2. How does water help in dissociation of acids and bases?

Ans: (i) The heat released in the dissolution process helps in the dissociation process by overcoming the forces that hold the hydrogen atom or the hydroxyl group in the molecules of the acid or the base, or in breaking the chemical bond holding them.

(ii) Presence of water weaken the electrostatic forces between anion and cations.

3. Identify the nature of the following aqueous solutions (whether acidic, basic or neutral):

(a) Solution A: [H+] < [OH–].

Ans: Solution A – basic.

(b) Solution B: [H+] > [OH–].

Ans: Solution B – acidic.

(c) Solution C: [H+] = [OH–]. 

Ans: Solution C – neutral.


1. POH of a solution is 5.2. What is its pH. Comment on the nature (acidic, basic or neutral) of this solution.

Ans: Since pH + pOH = 14

 pH = 14 – pOH = 14 – 5.2

= 8.8.

Since pH > 7.0, it is basic in nature.

2. pH of a solution is 9. What is the concentration of H+ ions in it.

Ans: pH = –log[H+] = 9. 

∴ log[H+] = –9.


[H+] = 10–9 mol L–1.

3. What is the nature (whether acidic, basic or neutral) of the following solutions?

(a) Solution A: pH = pOH.

Ans:  Solution A — neutra.

(b) Solution B: pH > pOH. 

Ans: Solution B — basic (since [H+] < [OH–] in it).

(c) Solution C: pH < pOH.

Ans: Solution C — acidic (since [H+] > [OH–] in it).


1. Identify acid radical and basic radical in CaSO4. 

Ans: 1. Acid radical SO42–.

Basic radical Ca2+.

2. CuSO4 was prepared by reacting an acid and a base. Identify the acid and the base that must have been used in this reaction.

Ans: Acid: H2SO4 (corresponding to the acid radical SO4 2–) Base: Cu(OH)2 (corresponding to the basic radical Cu2+).  

3. Which one of the following is the correct formula of plaster of paris? CaSO4.H2O or 2CaSO4.H2O.

Ans: (a) Carbonates.

(b) potassium salts.


I. Mark the correct choice.

1. Lemon juice contains.

(a) Tartaric acid. 

(b) Ascorbic acid.

(c) Acetic acid.

(d) Lactic acid.

Ans: (a) tartaric acid. 

2. Aqueous solutions of acids conduct electricity. This shows that.

(a) They contain H+ ions.

(b) They contain OH– ion.

(c) They contain cations and anions.

(d) They contain both H+ and OH– ions. 

Ans: (c) They contain cations and anions.

3. Which of the following is not a strong acid?

(a) HCl

(b) HBr.

(c) HI.

(d) HF. 

Ans: (d) HF. 

4. Self dissociation of water produces. 

(a) a large number of H+ ions.

(b) a large number of OH– ions.

(c) H+ and OH– ions in equal numbers. 

(d) H+ and OH– ions in unequal numbers.

Ans: (c) H+ and OH– ions in equal numbers.

5. In any aqueous basic solution.

(a) [H+] > [OH–].

(b) [H+] < [OH–].

(c) [H+] = [OH–. 

(d) [H+] = 0.

Ans: (b) [H+] < [OH–].

6. In an aqueous solution of HCl which of the following species is not present? 

(a) H+.

(b) OH–.

(c) HCl. 

(d) Cl– 7.

Ans: (b) OH–.

7. Which of the following is not a raw material for manufacturing washing soda?

(a) Limestone.

(b) Ammonia.

(c) Slaked lime.

(d) Sodium chloride.

Ans: (b) Ammonia.

II. Mark the following statements as true (T) or false (F): 

1. Acids furnish H+ ions only in the presence of water. 

Ans: True.

2. Lime water turns blue litmus red. 

Ans: False.

3. HF is a strong acid. 

Ans: False.

4. H2 gas is produced when acids react with metal oxides. 

Ans: True. 

5. Corrosive action of acids is due to H+ ions present in them. 

Ans: True. 

6. When the pH of the rain water becomes more than 5.6 it is called acid rain.

Ans: True.

7. Aqueous solutions of all the salts are neutral in nature i.e. neither acidic nor basic in nature.

Ans: True.

III. Fill in the blanks:

1. Acids taste …………………. while bases taste …………………. 

Ans: sour and bitter.

2. Milk of magnesia turns …………………. litmus ………………….

Ans: Red and Blue. 

3. One mole of sulphuric acid would furnish …………………. mole/s of H+ ions and …………………. moles of SO4 2– ions.

Ans: Blue and yellow.

4. …………………. gas is produced when acids react with metal hydrogen carbonates

Ans: 2 and 1.

5. Lime water turns milky on passing CO2 gas due to the formation of …………………. 

Ans: H2.

6. The reaction between an acid and a base is known as …………………. 

Ans: Neutralisation.

7. Bee sting injects …………………. acid which causes severe pain and burning sensation. 

Ans: Formic acid.

8. In NH4NO3 the acid radical is …………………. and the basic radical is …………………. 

Ans: NO3- (nitrate) and NH4+ (ammonium).

9. Chemically baking soda is …………………..

Ans: sodium bicarbonate (NaHCO3).

B. Descriptive Questions. 

1. What is an acid?

Ans: An acid is a chemical substance that donates protons or accepts pairs of electrons. In simpler terms, acids are compounds that release hydrogen ions (H⁺) when dissolved in water. Acids often have a sour taste, can turn blue litmus paper red, and react with bases to form salts and water in a chemical reaction called neutralisation. 

2. Give two examples of acids found in food articles.

Ans: Two examples of acids founds in food articles are mentioned below:  

(i)  Citric acid found in citrus fruits like lemon, oranges.

(ii) Grapefruit.

3. What is a base?

Ans: A base is a type of substance that your child may begin learning about in secondary school chemistry.

4. Give two examples of bases.

Ans: Two examples of bases are mentioned below:

(i) Sodium hydroxide is working as base.

(ii) The lime water is the example of base.

5. What are indicators?

Ans: An indicator is a chemical compound that changes its colour in presence of an acid or base. Indicators are generally derived from plant pigments and are mildly acidic or basic in nature.

6. What is the colour of methyl orange indicator in

(i) Acidic medium. 

Ans: In acidic medium the colour of methyl orange is red.

(ii) Basic medium.

Ans: In basic medium the colour of it is yellow.

7. Why do solutions of acids and bases conduct electricity?

Ans: Acids, when dissolved in water release the H+ and bases when dissolved in water release the OH- ions. These ions are charged species and so act as charge carriers. In other words the conductivity of these solutions is due to the movement of these ions.

8. Differentiate between strong and weak acids and give one example of each.

Ans: The different between strong and weak  are mentioned below: 

9. Write down the reaction between zinc and sulphuric acid.

Ans: Balanced equation for the reaction between zinc and dilute sulphuric acid is: Zn+H2SO4(dil)→ZnSO4+2H2.

10. Which gas is evolved when an acid reacts with metal carbonates? Which other category of compounds would produce the same gas on reacting with acids?

Ans: When an acid is added to metal carbonate, it results in the formation of salt, Water ( H2O) along with the evolution of Carbon dioxide gas.

11. What type of oxides react with acids? Give one examples of this type of oxide and write down the balanced equation for the reaction.

Ans: Metal oxides have properties of bases. Metal oxides can react with acids. The reaction of metal oxide with acid is a neutralisation reaction.

The balanced chemical equation for the reaction between calcium oxide and hydrochloric acid is: 𝐶𝑎𝑂(𝑠)+2𝐻𝐶𝑙(𝑎𝑞)→𝐶𝑎𝐶𝑙2(𝑎𝑞)+𝐻2𝑂(𝑙).

12. What is the name given to the reaction between an acid and a base? What are the products formed in such reactions?

Ans: If an acid and base react with each other then this reaction is known as neutralise reaction. NaOH + HCl —> NaCl + H2O.

13. “Corrosive action of acids is not related to their strength”. Justify this statement.

Ans: The corrosive action of acids is not related to their strength – If we talk about this reaction then we will see that the surface of the body is affected by the moisture present in the air which is the action of hydrolysis or water.

14. Give one example each of the following.

(i) a strong base.

Ans: Examples are: hydrochloric acid, nitric acid and sulphuric acid. 

(ii) a weak base.

Ans: Examples of weak acids include: acetic acid (vinegar), lactic acid, citric acid, and phosphoric acid.

15. List three categories of substances that can react with a base. Give one example of each and write the chemical reaction involved in each case.

Ans:  NH4OH + HCl —-> NH4Cl + H2O.

2NaOH + CO2 —-> Na2CO3 + H2.

16. What happens when a dry strip of each of red litmus paper and blue litmus paper is brought in contact with HCl gas? In which case a change would be observed if the strips are moistened and then brought in contact with HCl gas and what would be the change?

Ans: The colour of litmus paper changes only in the presence of ions like hydrogen (H+) or hydronium (H3O+) ions. 

HCl can produce these ions only in the form of aqueous solution. Hence dry HCl gas does not change the colour of dry litmus paper.

17. A small palette of NaOH is kept on dry red litmus paper. Initially, no change is observed but after some time its colour starts changing to blue around the place where the palette of NaOH is kept. Explain these observations.

Ans: A dry litmus paper will not show any effect in the presence of NaOH because there is no moisture available. Sodium hydroxide (NaOH) is dry initially therefore it does not show any change. After sometimes by absorbing moisture it becomes wet, therefore it changes from red litmus to blue.

18. How does water help in dissociation of acids and bases? Explain.

Ans: There are hydrogen ion or H (+) and the hydroxyl ions (OH-) present in the water which react with the acid and base and makes the compound of oxide and produced the hydrogen gas.

19. What is ‘self dissociation of water’? Name the resulting species and give their concentrations at 25°C.

Ans: The “self-dissociation of water” refers to the process by which water molecules spontaneously dissociate or break apart into ions in a pure water solution. Water molecules can dissociate into a positively charged hydrogen ion (H⁺) and a negatively charged hydroxide ion (OH⁻). This process occurs naturally due to the slight tendency of water molecules to ionise, leading to a dynamic equilibrium between water molecules and its ions.

The resulting species and give their concentrations at 25°C.

(i) Hydronium ion (H3O+)

(ii) Hydroxide ion (OH-)

20. What is ionic product constant of water? Give its value at 25°C. Will the value change if an acid, base or a salt is dissolved in water?

Ans:  The ionic product constant express by the formula,

K(w)=[H3O+][OH-] , at 25 degree Celsius value is 1*10-14 mile 2 /l-2.

21. Give the relationships between the concentrations of hydrogen ions and hydroxyl ions in.

(i) Pure water. 

Ans: The concentration of hydrogen ions and hydroxide ions is equal. 

(ii) A neutral solution. 

Ans: The hydrogen ion (H+) and the hydroxyl ion (OH) concentrations are equal, and each is equal to 10−7. A pH of 7 is neutral.

(iii) An acidic solution.

Ans: An acidic solution has the greater number of hydrogen ions than the hydroxyl ions.

(iv) A basic solution.

Ans: In basic medium the hydroxyl ions concentration is more than the hydrogen ions.

22. What is pH? What happens to the pH if the hydroxyl ion concentration in the solution increases?

Ans: The pH is the logarithmic value of concentration of hydrogen ions in a solution. 

If the PH value is increasing then we can say that the concentration of hydrogen in that solution is increasing.

23. Predict whether a given aqueous solution is acidic, basic or neutral if its pH is.

(a) 7.0. 

(b) 11.9. 

(c) 3.2.

Ans: (a) 7.0. 

A given aqueous solution is neutral when pH = 7, basic when   pH = 11.9 an  acidic when pH = 3.2.

24. Calculate the pH of 1.0 ×10–4 molar solution of HNO3. 

Ans: – pH=-log(H+).

Or, pH= -log (10^-4).

Or, pH=4.

25. What is the pH of 1.0 × 10–5 molar solution of KOH?

Ans: pH=-log(H+).

Or, pH= -log (10^-5).

Or, pH=5.

26. What is the pH of 1.0 × 10–2 mol L–1 solution of NaCl?

Ans: pH=-log(H+).

Or, pH=-log (10^-2).

Or, pH=2.

27. What do you understand by the term ‘universal indicator’?

Ans: A universal indicator is a mixture of different types of indicators that exhibits different coloration at different pH levels. It is used to detect the acidic or basic nature of a substance or a solution. It can be in the form of a paper strip or a solution. Example: Methyl red, and Phenolphthalein.

28. What is acid rain?

Ans: Acid is the mixture of water and the toxic gas present in the air. It affects the monument or the marbles present in open area. H2O + SO2 —-> H2SO4.

29. What is the importance of pH for humans and animals, and our digestive system?

Ans: pH plays a very important role in the digestion of food in our stomach. In the stomach, the secretion of hydrochloric acid happens which changes the stomach pH between one to three and this pH range is responsible for the activation of the pepsin enzyme which will digest the food.

30. Which chemical causes pain and burning sensation when somebody accidentally touches ‘nettle plant’? 

Ans: Accidental touch of Nettle leaves creates a pain and burning sensation due to the injection of methanoic acid into the skin.

31. What is a salt? Give two examples.

Ans: salt (NaCl), mineral substance of great importance to human and animal health, as well as to industry. The mineral form halite, or rock salt, is sometimes called common salt to distinguish it from a class of chemical compounds called salts.

Two examples are mentioned below:

(i) NaOH + HCl —-> NaCl + H2O.

(ii)  Copper sulphate.  

32. How are salts obtained from an acid? Mention four types of substances that can be used for it.

Ans: The reaction of acid with the basic substance makes the salt. For example, various acid or basic substances like NaOH, HC, MgO, CaO, NH4Cl etc.

33. Give chemical formula of.

(i) Baking soda.

Ans: NaHCO3.

(ii) Washing soda.

Ans: Na2CO3 .10 H2O.

34. List the raw materials required for the manufacture of baking soda and describe the process with the help of suitable chemical equations.

Ans: Washing soda is manufactured by Solvey’s process. We have already learnt about the raw materials required and part of the process in the manufacture of baking soda. Sodium carbonate is obtained by calcination (strong heating in a furnace) of sodium hydrogen carbonate and then recrystallisation from water:

 2NaHCO3 heat ⎯⎯⎯→ Na2CO3 + H2O + CO2

 Na2CO3 + 10H2O ⎯→ Na2CO3.10H2O

 sodium carbonate         washing soda.

35. Distinguish between baking powder and baking soda. Why is baking powder preferred for making cakes?

Ans: The raw materials required to manufacture washing soda, Lime stone, Sodium chloride (NaCl) in the form of brine, Ammonia (NH3).

CaCO3(s) ⎯→ CaO(s) + CO2(g)

NaCl(aq) + CO2(g) + NH3(g) + H2O(l) ⎯→ NaHCO3(s)↓ + 


2NaHCO3⎯⎯→ Na2CO3 + H2O + CO2.

36. Give any two uses of baking soda.

Ans: Two use of baking soda are mentioned below: 

(i) In preparation of baking powder.

(ii) In making cold drinks.

37. What is washing soda? Give its chemical formula. How is it manufactured by Solvey’s method?

Ans: Washing soda is used for washing of clothes. It is mainly because of this chemical that the clothes washed by a washerman appear so white. Chemically, washing soda is sodium carbonate decahydrate, Na2CO3.10H2O.

Washing soda is manufactured by Solvey’s process. We have already learnt about the raw materials required and part of the process in the manufacture of baking soda. Sodium carbonate is obtained by calcination (strong heating in a furnace) of sodium hydrogen carbonate and then recrystallisation from water:

2NaHCO3 heat ⎯⎯⎯→ Na2CO3 + H2O + CO

Na2CO3 + 10H2O ⎯→ Na 2CO3.10H2O

sodium carbonate       washing soda.

38. Give two uses of washing soda.

Ans: Two use of washing soda are mentioned below: 

(i) It is used as a laboratory reagent.

(ii) It is used in removing stains.

39. What is the chemical formula of ‘plaster of paris’? How is it manufactured? What precaution is taken during its manufacture.

Ans: You must have seen some beautiful designs made on the ceiling. Emically  it is 2CaSO4.H2O or CaSO4+ 1/ 2 H2O  (calcium sulphate hemihydrate).and walls of rooms in many houses. These are made of plaster of paris, also called POP.  

Raw material: –

Gypsum or CaSO4.2H2O

CaSO4.2H2O ⎯⎯⎯⎯⎯→ CaSO4.1/2H2O + 3/2H2O. 

40. List any four uses of ‘plaster of paris’.

Ans: Four uses of ‘plaster of paris are mentioned below: 

(i) Used in making casts and patterns for moulds and statue.

(ii) Used as cement in ornamental casting and for making decorative materials.

(ii) Used as a fire proofing material and for making chalks.

(ii) Used in hospitals for immobilising the affected part in case of bone fracture or strain.

41. What is bleaching? Chemically, what is bleaching powder? Give its any four uses.

Ans: Bleaching, a process of whitening fabric by removal of natural colour, such as the tan of linen, is usually carried out by means of chemicals selected according to the chemical composition of the fibre. Chemical bleaching is usually accomplished by oxidation. 

The chemical formula of bleaching powder is CaOCl2. Its chemical name is ‘calcium hypochlorite’. It is a white powder, it is also called ‘chloride of lime’. It is also called bleaching powder which gives off the smell of chlorine.

(i) Used as an oxidising agent in chemical industries.

(ii) Used for disinfection of drinking water.

(iii) Used for bleaching washed clothes in the laundry.

(iv) Used for bleaching wood pulp in the paper manufacturing industry.

42. List the raw materials required and the method of manufacture of bleaching powder. Write the equation for the reaction involved.

Ans: Bleaching powder is prepared by passing dry chlorine gas over dry slaked lime. 

The reaction being essentially 2 C a ( O H ) 2 + 2 C l 2 → C a

( O C l ) 2 + C a C l2 + 2 H 2 O.

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