Class 10 Science · Chapter 2

Acids, Bases and Salts

352 Class 10 Science questions on Acids, Bases and Salts from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 10 of 18

1. Q181 CBSE 2025
   1. (i)Give ​the ​relation between hydrogen ion concentration of an aqueous solution and its pH.
   2. (ii)Concentrated acids should not be diluted by ​adding water to ​acid. Why ?
   3. (iii)​Why do same molar concentrations of hydrochloric acid and acetic acid not produce same amounts ​of hydrogen ions ?
   Show answer

   Higher hydrogen-ion concentration means lower pH; diluting acid is exothermic, so acid goes into water; hydrochloric acid ionises fully, acetic acid partly.

   (i) The pH of a solution decreases as its hydrogen-ion concentration increases: the higher the concentration of hydrogen ions, the lower the pH (below $7$ acidic, $7$ neutral, above $7$ basic); in symbols, $\text{pH}=-{\log }_{10}[{\text{H}}^{+}]$. (ii) Dissolving an acid in water is highly exothermic. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns, and the glass container may break due to excessive local heating; so the acid is added slowly to water, with constant stirring. (iii) Hydrochloric acid is a strong acid and ionises completely in water, whereas acetic acid is a weak acid and ionises only partially, so the same molar concentration of acetic acid produces far fewer hydrogen ions.

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2. Q182 CBSE 2025
   Give reason ​:

   1. (i)Crystals of washing soda change to white ​powder on exposure to air.
   2. (ii)Plaster of Paris should be stored ​in moisture-proof containers.
   3. (iii)Baking soda can be used on bee ​sting area to ​get ​relief.
   4. (iv)Distilled water does ​not conduct electricity.
   5. (v)Farmers treat the soil ​of their fields with quick lime.
   Show answer

   Washing soda loses water of crystallisation, Plaster of Paris sets with moisture, distilled water has no ions, and bases neutralise acids.

   (i) Washing soda crystals, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$, lose most of their water of crystallisation on exposure to air and change to the white powder ${\text{Na}}_2{\text{CO}}_3\cdot {\text{H}}_2\text{O}$. (ii) Plaster of Paris takes up moisture and sets into a hard mass of gypsum, ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$, so it must be kept dry until it is used. (iii) A bee sting leaves an acid, which causes pain and irritation; baking soda is a mild base that neutralises it. (iv) Distilled water contains practically no ions, and ions are needed to carry a current through water. (v) Quick lime is a base; it neutralises the excess acidity of the soil and makes it suitable for crops.

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3. Q183 CBSE 2025
   Seawater contains many salts dissolved in it. Common salt ​is ​separated ​from these salts. Deposits of solid salt are also ​found in several parts of the world. ​These large crystals are ​often brown due to impurities. ​This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.

   1. (a)Write balanced chemical equations to show the products formed during electrolysis of brine.[1]
   2. (b)List two uses of any one product obtained during electrolysis of brine.[1]
   3. (c)(i)A mild non-corrosive basic salt ‘A’, used for faster cooking, is strongly heated to produce a compound ‘B’, that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated.[2]
   4. (c)(ii)OR : Define water of crystallisation. Give two examples of salts that have water of crystallisation.[2]
   Show answer

   Brine electrolysis gives $\text{NaOH}$, ${\text{Cl}}_2$ and ${\text{H}}_2$; A is baking soda, B is sodium carbonate; water of crystallisation is fixed water in a salt.

   (a) $2\text{NaCl(aq)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{Cl}}_2\text{(g)}+{\text{H}}_2\text{(g)}$ - chlorine is given off at the anode, hydrogen at the cathode and sodium hydroxide solution is formed near the cathode. (b) Sodium hydroxide is used (i) in the manufacture of soaps and detergents and (ii) for de-greasing metals; paper making and artificial fibres are equally acceptable. (c)(i) A is sodium hydrogencarbonate, baking soda, ${\text{NaHCO}}_3$; B is sodium carbonate, ${\text{Na}}_2{\text{CO}}_3$, which after recrystallisation is washing soda, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$. The equation is $2{\text{NaHCO}}_3\stackrel{\Delta }{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$. (c)(ii) Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt; two examples are copper sulphate pentahydrate ${\text{CuSO}}_4\cdot 5{\text{H}}_2\text{O}$ and washing soda ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$.

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4. Q184 CBSE 2025
   Acid-base indicators can be ​used to ​distinguish between an acid and a base. Universal indicator, a mixture of ​several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution ​is measured by pH paper, ​which is ​a paper impregnated with a universal indicator. Answer the following questions :

   1. (a)Solution P is a strong acid while solution Q is a strong base. On the pH scale, where would you place the solutions P and Q ?[1]
   2. (b)A solution has a pH of 7. Name a compound you would use to (i) increase its pH, and (ii) decrease its pH.[1]
   3. (c)(i)When the pH of a solution is decreased from 4 to 2, what effect does it produce on its hydronium ion concentration ? State the colour change shown by the pH paper.[2]
   4. (c)(ii)OR : A person is feeling pain and irritation in the stomach due to indigestion. What could be the pH of the fluid in the stomach ? Write the common name of the medicines people use for remedy. Give the chemical name of “milk of magnesia” often used for this purpose.[2]
   Show answer

   P is near pH 0 and Q near pH 14; the hydronium ion concentration becomes 100 times greater, turning pH paper orange to red.

   (a) P, being a strong acid, is placed at the extreme left of the scale, close to 0 (about pH 0 to 2); Q, being a strong base, is placed at the extreme right, close to 14 (about pH 12 to 14). (b) (i) To increase the pH, add a base such as sodium hydroxide, $\text{NaOH}$; (ii) to decrease the pH, add an acid such as hydrochloric acid, $\text{HCl}$. (c)(i) The hydronium ion concentration rises from $10^{-4}$ mol L${}^{-1}$ to $10^{-2}$ mol L${}^{-1}$, that is, it becomes $100$ times greater; the pH paper changes colour from orange (at pH 4) to red (at pH 2). (c)(ii) The fluid in the stomach is strongly acidic, of pH about 1.2 to 2. The medicines used for relief are called antacids, and the chemical name of milk of magnesia is magnesium hydroxide, ${\text{Mg(OH)}}_2$.

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5. Q185 CBSE 2025
   Common salt is ​a very important chemical compound for our daily life. It's chemical name is sodium chloride and it is ​used ​as ​a raw material in the manufacture ​of caustic soda, washing soda, baking soda ​etc. It is also used ​in the preservation of pickles, butter, meat etc.

   1. (i)Name the acid and the base from which common salt can be obtained.[1]
   2. (ii)State the nature (acidic/basic/neutral) of sodium chloride. Give reason for the justification for your answer.[1]
   3. (iii)(A)What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained.[2]
   4. (iii)(B)OR : How is washing soda obtained from sodium chloride? Give chemical equation of the reactions involved in the process.[2]
   Show answer

   Common salt is neutral and comes from $\text{HCl}$ and $\text{NaOH}$; brine electrolysis gives chlorine, hydrogen and sodium hydroxide; the ammonia-soda route gives washing soda.

   (i) Acid: hydrochloric acid $\text{HCl}$; base: sodium hydroxide $\text{NaOH}$, which neutralise as $\text{NaOH}+\text{HCl}\to \text{NaCl}+{\text{H}}_2\text{O}$. (ii) Neutral, pH $=7$, because sodium chloride is the salt of a strong acid ($\text{HCl}$) and a strong base ($\text{NaOH}$), so neither ${\text{Na}}^{+}$ nor ${\text{Cl}}^{-}$ reacts with water. (iii)(A) The brine decomposes - this is the chlor-alkali process: $2\text{NaCl}(aq)+2{\text{H}}_2\text{O}(l)\to 2\text{NaOH}(aq)+{\text{Cl}}_2(g)+{\text{H}}_2(g)$. Chlorine gas is given off at the anode, hydrogen gas at the cathode, and sodium hydroxide solution is formed near the cathode. (iii)(B) By the ammonia-soda route: $\text{NaCl}+{\text{H}}_2\text{O}+{\text{CO}}_2+{\text{NH}}_3\to {\text{NH}}_4\text{Cl}+{\text{NaHCO}}_3$; then $2{\text{NaHCO}}_3\stackrel{\text{Heat}}{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$; then ${\text{Na}}_2{\text{CO}}_3+10{\text{H}}_2\text{O}\to {\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$, which is washing soda.

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6. Q186 CBSE 2024
   When 2 mL of ​sodium hydroxide solution is added to few pieces of ​granulated zinc in ​a test tube and then warmed, the ​reaction that ​occurs ​can ​be ​written in the form of a balanced chemical equation as :

   1. (a)$\text{NaOH}+\text{Zn}\to {\text{NaZnO}}_2+{\text{H}}_2\text{O}$
   2. (b)$2\text{NaOH}+\text{Zn}\to {\text{Na}}_2{\text{ZnO}}_2+{\text{H}}_2$
   3. (c)$2\text{NaOH}+\text{Zn}\to {\text{NaZnO}}_2+{\text{H}}_2$
   4. (d)$2\text{NaOH}+\text{Zn}\to {\text{Na}}_2{\text{ZnO}}_2+{\text{H}}_2\text{O}$
   Show answer

   (b) $2\text{NaOH}+\text{Zn}\to {\text{Na}}_2{\text{ZnO}}_2+{\text{H}}_2$

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7. Q187 CBSE 2024
   Juice ​of ​tamarind turns ​blue litmus to red. It is because ​of the presence of ​an ​acid called :

   1. (a)methanoic acid
   2. (b)acetic acid
   3. (c)tartaric acid
   4. (d)oxalic acid
   Show answer

   (c) tartaric acid

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8. Q188 CBSE 2024
   Select a ​pair ​of natural ​indicator ​from ​the following :

   1. (a)Litmus and methyl orange
   2. (b)Turmeric and Litmus
   3. (c)Phenolphthalein and methyl orange
   4. (d)Methyl orange and Turmeric
   Show answer

   (b) Turmeric and Litmus

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9. Q189 CBSE 2024
   An aqueous solution of a salt ​turns blue litmus to ​red. ​The salt ​could be the one obtained by ​the reaction of :

   1. (a)${\text{HNO}}_3$ and $\text{NaOH}$
   2. (b)${\text{H}}_2{\text{SO}}_4$ and $\text{KOH}$
   3. (c)${\text{CH}}_3\text{COOH}$ and $\text{NaOH}$
   4. (d)$\text{HCl}$ and ${\text{NH}}_4\text{OH}$
   Show answer

   (d) $\text{HCl}$ and ${\text{NH}}_4\text{OH}$

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10. Q190 CBSE 2024
    The ​acid ​produced in ​our stomach during digestion and the base ​used to ​neutralise the ​excess acid ​during indigestion respectively are :

    1. (a)$\text{HCl}$, ${\text{Mg(OH)}}_2$
    2. (b)$\text{HCl}$, ${\text{Ca(OH)}}_2$
    3. (c)Amino acids, ${\text{Ca(OH)}}_2$
    4. (d)Lactic acid, ${\text{Mg(OH)}}_2$
    Show answer

    (a) $\text{HCl}$, ${\text{Mg(OH)}}_2$

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11. Q191 CBSE 2024
    A ​few drops of ​turmeric solution are added ​to a colourless ​liquid. If the liquid ​becomes ​red, the ​liquid may be ​:

    1. (a)Hydrochloric acid
    2. (b)Distilled water
    3. (c)Ammonium hydroxide
    4. (d)Lemon juice
    Show answer

    (c) Ammonium hydroxide

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12. Q192 CBSE 2024
    Bleaching powder ​can be prepared ​by ​reacting ​:

    1. (a)Baking power with chlorine
    2. (b)Washing soda with chlorine
    3. (c)Baking soda with chlorine
    4. (d)Slaked lime with chlorine
    Show answer

    (d) Slaked lime with chlorine

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13. Q193 CBSE 2024
    A chemical ​compound ​used ​in ​glass, soap ​and paper ​industries is

    1. (a)Washing Soda
    2. (b)Baking Soda
    3. (c)Bleaching Powder
    4. (d)Common Salt
    Show answer

    (a) Washing Soda

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14. Q194 CBSE 2024
    Four solutions, namely ​glucose, alcohol, hydrochloric acid and sulphuric acid filled in four separate ​beakers are connected one ​by one in ​an electric ​circuit with a bulb. The ​solutions in which the bulb will glow when current ​is ​passed are :

    1. (a)Glucose and alcohol
    2. (b)Alcohol and hydrochloric acid
    3. (c)Glucose and sulphuric acid
    4. (d)Hydrochloric acid and sulphuric acid
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    (d) Hydrochloric acid and sulphuric acid

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15. Q195 CBSE 2024
    The salt ​present ​in tooth ​enamel is ​:

    1. (a)Calcium phosphate
    2. (b)Magnesium phosphate
    3. (c)Sodium phosphate
    4. (d)Aluminium phosphate
    Show answer

    (a) Calcium phosphate

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16. Q196 CBSE 2024
    An aqueous solution ‘A’ turns ​phenolphthalein solution ​pink. When another ​aqueous solution ‘B’ is added to the pink ​solution, the pink colour ​disappears. Now when a few drops of solution ‘A’ are ​added to this reaction, the mixture appears pink again. The ​respective changes in the nature of the solution are ​from :

    1. (a)acidic → basic → basic
    2. (b)basic → acidic → acidic
    3. (c)acidic → basic → acidic
    4. (d)basic → acidic → basic
    Show answer

    (d) basic → acidic → basic

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17. Q197 CBSE 2024
    Identify the ​pair of ​natural indicators ​from the ​following :

    1. (a)Turmeric and methyl orange
    2. (b)Phenolphthalein and methyl orange
    3. (c)Litmus and turmeric
    4. (d)Litmus and methyl orange
    Show answer

    (c) Litmus and turmeric

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18. Q198 CBSE 2024
    The acid ​present ​in ​nettle ​sting ​is ​:

    1. (a)Acetic acid
    2. (b)Methanoic acid
    3. (c)Tartaric acid
    4. (d)Citric acid
    Show answer

    (b) Methanoic acid

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19. Q199 CBSE 2024
    The ​chemical ​formula ​of ​Gypsum is ​:

    1. (a)${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$
    2. (b)${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$
    3. (c)${\text{CaSO}}_4\cdot {\text{H}}_2\text{O}$
    4. (d)${\text{CaSO}}_4\cdot 5{\text{H}}_2\text{O}$
    Show answer

    (b) ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$

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20. Q200 CBSE 2024
    An ​aqueous solution of sodium chloride ​is ​prepared in distilled ​water. ​The pH of this solution ​is :

    1. (a)$6$
    2. (b)$8$
    3. (c)$7$
    4. (d)$3$
    Show answer

    (c) $7$

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