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 11 of 18

1. Q201 CBSE 2024
   Identify ​from the following a ​compound used ​in ​paper, glass and ​soap ​industries.

   1. (a)Sodium chloride
   2. (b)Bleaching powder
   3. (c)Baking soda
   4. (d)Washing soda
   Show answer

   (d) Washing soda

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2. Q202 CBSE 2024
   Consider ​the following compounds ​: ${\text{FeSO}}_4$ ; ${\text{CuSO}}_4$ ​; ${\text{CaSO}}_4$ ; ${\text{Na}}_2{\text{CO}}_3$ The compound having maximum number of ​water ​of crystallisation ​in its crystalline form in one molecule is ​:

   1. (a)${\text{FeSO}}_4$
   2. (b)${\text{CuSO}}_4$
   3. (c)${\text{CaSO}}_4$
   4. (d)${\text{Na}}_2{\text{CO}}_3$
   Show answer

   (d) ${\text{Na}}_2{\text{CO}}_3$

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3. Q203 CBSE 2024
   Tooth decay ​begins ​at ​the ​pH of :

   1. (a)5.1
   2. (b)5.8
   3. (c)6.5
   4. (d)8.0
   Show answer

   (a) 5.1

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4. Q204 CBSE 2024
   The name of the ​compound ‘A’ ​formed ​in the following ​reaction ​is ​: $\text{NaCl}+{\text{NH}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2⟶\text{‘A’}+{\text{NH}}_4\text{Cl}$

   1. (a)Sodium carbonate
   2. (b)Ammonium carbonate
   3. (c)Sodium hydrogen carbonate
   4. (d)Ammonium hydrogen carbonate
   Show answer

   (c) Sodium hydrogen carbonate

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5. Q205 CBSE 2024
   Which among ​the ​following has ​minimum number of ​water of ​crystallisation ​?

   1. (a)Washing soda
   2. (b)Gypsum
   3. (c)Ferrous sulphate
   4. (d)Copper sulphate
   Show answer

   (b) Gypsum

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6. Q206 CBSE 2024
   The pH ​of an aqueous solution of a ​salt is $9$. The ​types of ​acid ​and base from ​which this salt is ​formed are :

   1. (a)weak acid and weak base
   2. (b)weak acid and strong base
   3. (c)strong acid and weak base
   4. (d)strong acid and strong base
   Show answer

   (b) weak acid and strong base

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7. Q207 CBSE 2024
   A colourless ​gas $G$ is produced when egg-shells ​are ​treated with a solution $S$. ​The gas $G$ turns lime water milky. $S$ ​and $G$ ​respectively are :

   1. (a)${\text{H}}_2{\text{SO}}_4$ and ${\text{SO}}_2$
   2. (b)$\text{HCl}$ and ${\text{SO}}_2$
   3. (c)$\text{NaCl}$ and ${\text{CO}}_2$
   4. (d)$\text{HCl}$ and ${\text{CO}}_2$
   Show answer

   (d) $\text{HCl}$ and ${\text{CO}}_2$

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8. Q208 CBSE 2024
   The ​experimental set-up, shown in the diagram, is used ​for testing the conductivity of a solution filled in the beaker. If we ​have four solutions, namely solutions of A – sugar, B – common salt, C – lemon juice ​and D – alcohol and fill them in the ​beaker one by one ​to test their conductivity, in ​which case/cases will ​the bulb glow ? Give reason to justify your answer.

   Show answer

   The bulb glows in B and C, because common salt and lemon juice give ions that carry current.

   The bulb glows in cases B (common salt) and C (lemon juice). Common salt is an ionic compound that gives ${\text{Na}}^{+}$ and ${\text{Cl}}^{-}$ ions in water, and lemon juice contains citric acid, which gives ${\text{H}}^{+}$ ions in water. These ions carry the current through the solution, so the circuit is complete. Sugar (A) and alcohol (D) are covalent compounds that dissolve as molecules and give no ions, so no current flows through their solutions and the bulb does not glow.

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9. Q209 CBSE 2024
   1 gram of solid sodium chloride was ​taken in a clean and ​dry test tube and concentrated ​sulphuric ​acid was added to it.

   1. (i)Name the gas evolved in the reaction.
   2. (ii)What will be observed when ​this gas is tested with (I) dry, and (II) wet blue litmus paper ? Write your conclusion about the nature ​(acidic/basic) of ​this gas.
   Show answer

   Hydrogen chloride gas; dry blue litmus is unchanged, wet blue litmus turns red, so the gas is acidic only with water.

   (i) Hydrogen chloride ($\text{HCl}$) gas is evolved. (ii) (I) Dry blue litmus paper shows no change — it stays blue; (II) Wet blue litmus paper turns red. Conclusion: hydrogen chloride gas is acidic in nature, but it shows its acidic character only in the presence of water, which lets it form ${\text{H}}^{+}$ (${\text{H}}_3{\text{O}}^{+}$) ions.

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10. Q210 CBSE 2024
    Some metals react with acids to ​produce salt and ​hydrogen gas. Illustrate it with an ​example. How ​will you test ​the presence of this gas ?
    Show answer

    Zinc and dilute sulphuric acid give zinc sulphate and hydrogen; hydrogen burns with a pop sound near a flame.

    Example: zinc granules react with dilute sulphuric acid to form zinc sulphate (the salt) and hydrogen gas: $\text{Zn}+{\text{H}}_2{\text{SO}}_4\to {\text{ZnSO}}_4+{\text{H}}_2\uparrow$. Test: pass the gas through soap solution and bring a burning candle near a gas-filled bubble (or bring a burning matchstick near the gas). The gas burns with a pop sound, which shows that it is hydrogen.

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11. Q211 CBSE 2024
    Write ​the chemical name and molecular formula of ​Plaster of Paris. Why should it ​be ​stored in ​a moisture ​proof container ?
    Show answer

    Calcium sulphate hemihydrate, ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$; it absorbs moisture and sets into hard gypsum.

    Chemical name: calcium sulphate hemihydrate. Molecular formula: ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$. It is stored in a moisture-proof container because Plaster of Paris takes up water from moist air and changes back into gypsum, ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$, which sets into a hard solid mass; the plaster would then be useless for moulding.

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12. Q212 CBSE 2024
    What is ​a ​neutralisation reaction ? Write the chemical ​equation for a ​neutralisation reaction and write the ​name of ​the salt produced.
    Show answer

    Neutralisation is the reaction of an acid with a base to give a salt and water; NaOH and HCl give sodium chloride.

    A neutralisation reaction is the reaction between an acid and a base to give a salt and water. Example: $\text{NaOH}+\text{HCl}\to \text{NaCl}+{\text{H}}_2\text{O}$. The salt produced is sodium chloride (common salt).

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13. Q213 CBSE 2024
    A compound ​‘X’ on ​heating ​at 373 K loses water molecules and becomes ​‘Y’. Substance ‘Y’ is used ​by doctors for supporting ​fractured ​bones in ​the right position.

    1. (i)Identify ‘X’ and ‘Y’.
    2. (ii)How can we obtain ‘X’ from ‘Y’?
    Show answer

    X is gypsum and Y is Plaster of Paris; mixing Y with water gives X back.

    (i) X is gypsum, ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$ (calcium sulphate dihydrate), and Y is Plaster of Paris, ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$ (calcium sulphate hemihydrate): ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}\stackrel{373\text{K}}{\to }{\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}$. (ii) X is obtained from Y by mixing Y with water; it takes up water and sets into a hard solid mass of gypsum: ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$.

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14. Q214 CBSE 2024
    Two solutions X and ​Y give red ​and blue colour respectively with universal indicator.

    1. (i)In which solution is the hydrogen ion concentration more than the other? Justify your answer.
    2. (ii)If X and Y are mixed in proper ​amounts and the resultant mixture ​is tested with a universal indicator, it ​turns ​green. What ​is the nature of the salt formed? Justify your answer.
    Show answer

    X, being acidic, has the higher hydrogen ion concentration; the mixture at pH 7 gives a neutral salt.

    (i) Solution X has the higher hydrogen ion concentration. The red colour shows that X is acidic, with a low pH (below 7), while the blue colour shows that Y is basic, with a pH above 7; the lower the pH, the higher the concentration of ${\text{H}}^{+}$ ions. (ii) The salt formed is a neutral salt. The mixture turns universal indicator green, which means pH 7: the acid X and the base Y have neutralised each other, and the solution of the salt formed is neither acidic nor basic (like sodium chloride, the salt of a strong acid and a strong base).

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15. Q215 CBSE 2024
    Write the common name and the ​chemical name ​of the compound ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$. Write ​the method ​of its preparation. Give chemical ​equation for the reaction, when water ​reacts ​with ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$.
    Show answer

    It is Plaster of Paris, calcium sulphate hemihydrate; gypsum heated at 373 K gives it, and with water it sets back into gypsum.

    Common name: Plaster of Paris. Chemical name: calcium sulphate hemihydrate. Preparation: gypsum (${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$) is heated at $373$ K; it loses water and forms Plaster of Paris: ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}\stackrel{373\text{K}}{\to }{\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}$. Reaction with water: on mixing with water, Plaster of Paris changes back into gypsum, giving a hard solid mass: ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$.

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16. Q216 CBSE 2024
    A small amount of copper oxide ​was taken in a beaker and dilute hydrochloric acid was added with continuous stirring of the solution. Name the compound formed ​and ​state the colour of its solution. ​Write balanced chemical equation ​for the reaction that occurs. Based ​on the ​reaction, ​state the nature (acidic/basic) of copper oxide.
    Show answer

    Copper(II) chloride forms, giving a blue-green solution: $\text{CuO}+2\text{HCl}\to {\text{CuCl}}_2+{\text{H}}_2\text{O}$; copper oxide is basic.

    The compound formed is copper(II) chloride, ${\text{CuCl}}_2$, and its solution is blue-green (the black copper oxide dissolves). Balanced equation: $\text{CuO}+2\text{HCl}\to {\text{CuCl}}_2+{\text{H}}_2\text{O}$. Nature: copper oxide reacts with an acid to form a salt and water, as a base does, so copper oxide is basic in nature (a basic oxide).

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17. Q217 CBSE 2024
    Consider the following salts :

    1. (i)$\text{XCl}$
    2. (ii)${\text{NH}}_4\text{Y}$
    3. (iii)${\text{ZCO}}_3$ Answer the following questions giving ​reason in each case. (a) If ‘X’ is sodium, what is the pH of $\text{XCl}$ ? (b) If ‘Y’ is sulphate, what colour would the aqueous solution of ${\text{NH}}_4\text{Y}$ ​give when a ​few ​drops of universal indicator are added to ​it ? (c) If ​‘Z’ is calcium, what would be ​the change in colour in blue litmus paper when a drop of ${\text{ZCO}}_3$ is poured on ​it ?
    Show answer

    NaCl has pH 7; ammonium sulphate solution is acidic and turns universal indicator orange; calcium carbonate is basic, so blue litmus is unchanged.

    (a) pH = 7. $\text{NaCl}$ is the salt of a strong acid ($\text{HCl}$) and a strong base ($\text{NaOH}$), so its solution is neutral. (b) Orange - an acidic colour, not green. With Y = sulphate the salt is ammonium sulphate, $({\text{NH}}_4{)}_2{\text{SO}}_4$, the salt of a strong acid (${\text{H}}_2{\text{SO}}_4$) and a weak base (${\text{NH}}_4\text{OH}$), so its solution is acidic, with pH less than 7. (c) No change: blue litmus stays blue. ${\text{CaCO}}_3$ is the salt of a weak acid (${\text{H}}_2{\text{CO}}_3$) and a strong base (${\text{Ca(OH)}}_2$), so it is basic, and only acids turn blue litmus red.

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18. Q218 CBSE 2024
    1. (i)The pH of ​a sample of tomato juice ​is $4.6$. How is this juice likely to be in taste ? Give reason to justify ​your answer.
    2. (ii)How ​do we differentiate ​between a strong acid and a weak base in terms of ion-formation in aqueous solutions ?
    3. (iii)The acid rain can make the ​survival of aquatic ​animals difficult. ​How ?
    Show answer

    Tomato juice is sour (pH 4.6, acidic); strong acids ionise completely, weak bases partially; acid rain lowers pond pH and harms aquatic animals.

    (i) The juice is likely to be sour in taste. Reason: its pH, $4.6$, is less than $7$, so it is acidic, and acids taste sour. (ii) A strong acid ionises completely in aqueous solution and gives a large number of ${\text{H}}^{+}$ ions (e.g. $\text{HCl}$); a weak base ionises only partially and gives a small number of ${\text{OH}}^{-}$ ions (e.g. ${\text{NH}}_4\text{OH}$). (iii) Rain with pH less than $5.6$ is acid rain. When it flows into rivers and lakes, it lowers the pH of the water; aquatic animals can survive only within a narrow range of pH, so their survival becomes difficult.

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19. Q219 CBSE 2024
    What is ​meant by the ​term pH ​of a solution ? The pH ​of rain water collected from two cities ‘A’ and ‘B’ was found ​to be 6.1 and 5.3 respectively. The water of which city is more acidic ? Justify your answer. State with reason what ​would happen to the aquatic life ​of a pond in which the rain water of city ‘B’ flows.
    Show answer

    City B is more acidic, as its lower pH means more hydrogen ions; its acid rain lowers the pond's pH and harms aquatic life.

    pH is a number on a scale from $0$ to $14$ that measures the hydrogen ion concentration of a solution: a pH of $7$ is neutral, below $7$ acidic and above $7$ basic, and the higher the hydrogen ion concentration, the lower the pH. The rain water of city B (pH $5.3$) is more acidic than that of city A (pH $6.1$), because a lower pH means a higher concentration of hydrogen ions. City B's rain, with a pH below $5.6$, is acid rain; flowing into the pond it lowers the pH of the pond water, and since living organisms can survive only within a narrow range of pH, the survival of aquatic life becomes difficult and the plants and animals may be harmed or die.

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20. Q220 CBSE 2024
    Study the experimental ​set-up ​shown in the diagram and answer the questions that follow :

    1. (i)Name the gas evolved and write the change observed in the lime ​water. Write chemical equation of the reaction.
    2. (ii)If the same gas is passed ​in excess in the product of ​the above reaction, what ​change is ​observed in the contents of the test tube ? Write the chemical formula ​of the new product formed.

    Show answer

    The gas is carbon dioxide, which turns lime water milky; excess gas clears it, forming calcium hydrogencarbonate, ${\text{Ca(HCO}}_3{)}_2$.

    (i) The gas evolved is carbon dioxide: ${\text{Na}}_2{\text{CO}}_3(s)+2\text{HCl}(aq)\to 2\text{NaCl}(aq)+{\text{H}}_2\text{O}(l)+{\text{CO}}_2(g)$. It turns the lime water milky, because a white precipitate of calcium carbonate forms: ${\text{Ca(OH)}}_2(aq)+{\text{CO}}_2(g)\to {\text{CaCO}}_3(s)+{\text{H}}_2\text{O}(l)$. (ii) When the gas is passed in excess, the milkiness disappears and the contents become clear again, because the calcium carbonate changes into calcium hydrogencarbonate, which is soluble in water: ${\text{CaCO}}_3(s)+{\text{H}}_2\text{O}(l)+{\text{CO}}_2(g)\to {\text{Ca(HCO}}_3{)}_2(aq)$. The new product is ${\text{Ca(HCO}}_3{)}_2$.

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