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 12 of 18

1. Q221 CBSE 2024
   A chemical compound which ​is obtained ​from baking soda is ​used in glass, soap and paper industries. Identify the compound. How ​is this compound obtained in its crystalline form ? ​State whether this compound is acidic/basic/neutral ​in ​nature. Justify ​your answer.
   Show answer

   The compound is sodium carbonate; recrystallisation gives washing soda, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$, which is basic.

   The compound is sodium carbonate, ${\text{Na}}_2{\text{CO}}_3$, obtained by heating baking soda: $2{\text{NaHCO}}_3\stackrel{\text{heat}}{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$. Its crystalline form, washing soda, is obtained by recrystallisation: ${\text{Na}}_2{\text{CO}}_3+10{\text{H}}_2\text{O}\to {\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$. It is basic in nature, because it is the salt of a strong base (sodium hydroxide) and a weak acid (carbonic acid); its aqueous solution has a pH more than 7 and turns red litmus blue.

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2. Q222 CBSE 2024
   1. (i)Identify ​the ​acid and the base ​from which the following salts are obtained ​: (I) Sodium chloride (II) Ammonium sulphate
   2. (ii)Write the nature, acidic/basic/neutral, of each of the above mentioned salts, giving ​reason for ​your ​answer.
   Show answer

   Sodium chloride (from hydrochloric acid and sodium hydroxide) is neutral; ammonium sulphate (from sulphuric acid and ammonium hydroxide) is acidic.

   (i) (I) Sodium chloride is obtained from hydrochloric acid, $\text{HCl}$, and sodium hydroxide, $\text{NaOH}$. (II) Ammonium sulphate is obtained from sulphuric acid, ${\text{H}}_2{\text{SO}}_4$, and ammonium hydroxide, ${\text{NH}}_4\text{OH}$. (ii) Sodium chloride is neutral (pH $7$) because it is the salt of a strong acid and a strong base. Ammonium sulphate is acidic (pH below $7$) because it is the salt of a strong acid and a weak base.

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3. Q223 CBSE 2024
   Write chemical equation to show the preparation of baking soda. How ​is baking powder prepared from baking soda ​? Explain ​how baking powder ​makes the bread ​or cake soft ​and spongy. Write chemical ​equation for the reaction which ​occurs when baking power is heated.
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   Baking powder is baking soda mixed with a mild edible acid; on heating it releases carbon dioxide, which makes bread and cake rise.

   Preparation of baking soda: $\text{NaCl}+{\text{H}}_2\text{O}+{\text{CO}}_2+{\text{NH}}_3\to {\text{NH}}_4\text{Cl}+{\text{NaHCO}}_3$. Baking powder is prepared by mixing baking soda (sodium hydrogencarbonate) with a mild edible acid such as tartaric acid. When the dough or batter is heated, or the powder is moistened, the acid reacts with the sodium hydrogencarbonate and releases carbon dioxide; the gas forms bubbles that are trapped in the dough and expand, so the bread or cake rises and becomes soft and spongy. Reaction when baking powder (printed "baking power") is heated: ${\text{NaHCO}}_3+{\text{H}}^{+}\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{sodium salt of acid}$.

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4. Q224 CBSE 2024
   When ​electricity is passed ​through an aqueous solution of common salt, three products are obtained. Name them, specifying the electrode at ​which each of ​these products is obtained. ​Also ​give one ​use of each product.
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   Chlorine at the anode, hydrogen at the cathode, and sodium hydroxide near the cathode.

   The three products of the chlor-alkali process, $2\text{NaCl}(\text{aq})+2{\text{H}}_2\text{O}(\text{l})\to 2\text{NaOH}(\text{aq})+{\text{Cl}}_2(\text{g})+{\text{H}}_2(\text{g})$, are: (1) Chlorine gas, given off at the anode; used for water treatment (disinfecting drinking water and swimming pools). (2) Hydrogen gas, given off at the cathode; used as a fuel. (3) Sodium hydroxide solution, formed near the cathode; used to make soaps and detergents.

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5. Q225 CBSE 2024
   A compound which is prepared from gypsum has the property of ​hardening when water ​is ​mixed in right quantity with it ​:

   1. (i)Write common name and the chemical name ​of this compound.
   2. (ii)Give chemical ​equation ​for its preparation.
   3. (iii)List its ​two uses.
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   Plaster of Paris, calcium sulphate hemihydrate, is made by heating gypsum at 373 K and is used for supporting fractured bones and making toys.

   (i) Common name: Plaster of Paris; chemical name: calcium sulphate hemihydrate, ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}$. (ii) It is prepared by heating gypsum at 373 K: ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}\stackrel{373\text{K}}{\to }{\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}$. (iii) Any two uses: as plaster for supporting fractured bones in the right position; for making toys; for making materials for decoration; for making surfaces smooth.

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6. Q226 CBSE 2024
   (i) Five solutions A, B, C, D and E when ​tested ​with pH paper showed pH as 4, 1, 13, 7 and 10 respectively. Which solution is :

   1. (1)Strongly acidic
   2. (2)Strongly alkaline
   3. (3)Weakly acidic
   4. (4)Neutral and
   5. (5)Weakly alkaline ​? ​Arrange the solutions in increasing order ​of ${\text{H}}^{+}$ ​ion concentration. (ii) Write the name ​and formula of (1) an acidic salt and (2) a basic salt giving the name of the parent acid and parent base used to form the salt in each case.
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   ${\text{H}}^{+}$ ion concentration increases in the order $\text{C}<\text{E}<\text{D}<\text{A}<\text{B}$; ${\text{NH}}_4\text{Cl}$ is an acidic salt and ${\text{Na}}_2{\text{CO}}_3$ a basic salt.

   (i) (1) Strongly acidic: B (pH 1); (2) Strongly alkaline: C (pH 13); (3) Weakly acidic: A (pH 4); (4) Neutral: D (pH 7); (5) Weakly alkaline: E (pH 10). Increasing order of ${\text{H}}^{+}$ ion concentration: $\text{C}<\text{E}<\text{D}<\text{A}<\text{B}$, because the lower the pH, the higher the ${\text{H}}^{+}$ ion concentration. (ii) (1) Acidic salt: ammonium chloride, ${\text{NH}}_4\text{Cl}$; parent acid hydrochloric acid ($\text{HCl}$, strong) and parent base ammonium hydroxide (${\text{NH}}_4\text{OH}$, weak). (2) Basic salt: sodium carbonate, ${\text{Na}}_2{\text{CO}}_3$; parent acid carbonic acid (${\text{H}}_2{\text{CO}}_3$, weak) and parent base sodium hydroxide ($\text{NaOH}$, strong).

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7. Q227 CBSE 2024
   A few crystals of ​ferrous sulphate were taken in a dry boiling tube and ​heated. Tiny water droplets were ​observed in the tube ​after some time.

   1. (i)From where did these water ​droplets appear ? Explain.
   2. (ii)What ​colour change will be observed during heating ?
   3. (iii)How many molecules of ​water are attached per molecule of ${\text{FeSO}}_4$ crystal ? Write the molecular formula of crystalline forms of (I) Copper sulphate, and (II) Sodium ​carbonate.
   4. (iv)State how is Plaster of Paris obtained from gypsum. Write two uses of Plaster of Paris.
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   Water of crystallisation of ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$ condenses as droplets; green crystals turn white; heating gypsum at 373 K gives Plaster of Paris.

   (i) The droplets are the water of crystallisation of ferrous sulphate. The crystals are ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$; heating drives this water out as vapour, which condenses as droplets on the cooler upper part of the dry tube. (ii) The pale green crystals turn white as they lose their water (anhydrous ${\text{FeSO}}_4$); on stronger heating they decompose, $2{\text{FeSO}}_4\to {\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$, leaving reddish-brown ferric oxide. (iii) Seven molecules of water per formula unit (${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$). (I) Copper sulphate: ${\text{CuSO}}_4\cdot 5{\text{H}}_2\text{O}$; (II) Sodium carbonate: ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$. (iv) Gypsum is heated at $373$ K: ${\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}$, and the hemihydrate is Plaster of Paris. Uses: supporting fractured bones in the right position; making toys and materials for decoration (also for making surfaces smooth).

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8. Q228 CBSE 2024
   Explain ​chlor-alkali process and write balanced chemical ​equations for the ​reactions that occur. Name the ​gases ​obtained at the ​anode ​and cathode respectively. Mention two uses each of the two gases ​obtained in the above process.
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   Brine electrolysis gives sodium hydroxide, chlorine at the anode and hydrogen at the cathode; chlorine treats drinking water, hydrogen is a fuel.

   Chlor-alkali process: when electricity is passed through brine (a concentrated aqueous solution of sodium chloride), it decomposes to form sodium hydroxide, chlorine and hydrogen; the name comes from chlor (chlorine) and alkali (sodium hydroxide). Overall equation: $2\text{NaCl}(aq)+2{\text{H}}_2\text{O}(l)\to 2\text{NaOH}(aq)+{\text{Cl}}_2(g)+{\text{H}}_2(g)$. At the anode: $2{\text{Cl}}^{-}\to {\text{Cl}}_2+2e^{-}$; at the cathode: $2{\text{H}}_2\text{O}+2e^{-}\to {\text{H}}_2+2{\text{OH}}^{-}$, so sodium hydroxide forms near the cathode. Gas obtained at the anode: chlorine; gas obtained at the cathode: hydrogen. Uses of chlorine: treatment of drinking water and swimming pools; manufacture of PVC, disinfectants, pesticides and bleaching powder. Uses of hydrogen: as a fuel; hydrogenation of vegetable oils to make margarine; manufacture of ammonia for fertilisers.

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9. Q229 CBSE 2024
   Name and state ​in brief the process which ​is used to prepare sodium hydroxide from sodium chloride. In this process along with the main product two gases ‘X’ and ‘Y’ ​are also ​given off at the two electrodes. Name ‘X’ ​and ‘Y’ specifying the name of their respective electrode at which each gas is obtained. One of ​these gases when reacts with dry calcium hydroxide ​produces a compound ‘Z’ which is widely used in ​water treatment plants and textile industries. Name Z and write chemical equation for the reaction involved in its formation.
   Show answer

   Chlor-alkali process; X is chlorine at the anode, Y is hydrogen at the cathode; Z is bleaching powder, ${\text{CaOCl}}_2$.

   The process is the chlor-alkali process: when electricity is passed through brine (an aqueous solution of sodium chloride), it decomposes to form sodium hydroxide, and chlorine and hydrogen are given off: $2\text{NaCl(aq)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{Cl}}_2\text{(g)}+{\text{H}}_2\text{(g)}$. X is chlorine gas, given off at the anode (positive electrode), and Y is hydrogen gas, given off at the cathode (negative electrode). Sodium hydroxide solution is formed near the cathode. Z is bleaching powder, ${\text{CaOCl}}_2$, formed when chlorine reacts with dry slaked lime: ${\text{Ca(OH)}}_2+{\text{Cl}}_2\to {\text{CaOCl}}_2+{\text{H}}_2\text{O}$.

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10. Q230 CBSE 2024
    An acid ‘X’ present in tamarind when mixed with ‘Y’, ​produces a mixture ‘Z’. ‘Z’ on addition to a ​dough when heated makes cakes soft and spongy. ‘Y’ is prepared from ​common salt and helps in faster cooking.

    1. (i)Write the common ​names ​of ‘X’, ‘Y’ and ‘Z’, and the chemical formula ​of ‘Y’.
    2. (ii)How is ​‘Y’ prepared and how does it help in making cakes soft and spongy ? Illustrate the reaction with suitable chemical ​equation.
    3. (iii)Write the name and chemical formula of a mild base other than ‘Y’ used as an antacid.
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    X is tartaric acid, Y baking soda (${\text{NaHCO}}_3$), Z baking powder; it releases carbon dioxide that makes cakes spongy; antacid: ${\text{Mg(OH)}}_2$.

    (i) X: tartaric acid; Y: baking soda (sodium hydrogencarbonate), ${\text{NaHCO}}_3$; Z: baking powder. (ii) Y is prepared from sodium chloride: $\text{NaCl}+{\text{H}}_2\text{O}+{\text{CO}}_2+{\text{NH}}_3\to {\text{NH}}_4\text{Cl}+{\text{NaHCO}}_3$. When baking powder in the dough is heated or mixed with water, the baking soda reacts with the acid and releases carbon dioxide: ${\text{NaHCO}}_3+{\text{H}}^{+}\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{sodium salt of acid}$ (heated alone, $2{\text{NaHCO}}_3\to {\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$). The carbon dioxide makes the dough rise, so the cake is soft and spongy. (iii) Magnesium hydroxide (milk of magnesia), ${\text{Mg(OH)}}_2$.

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11. Q231 CBSE 2024
    Common salt is a ​very important raw material as ​many ​compounds ​of industrial use can be ​prepared from it. Explain, giving chemical equations, the method ​of preparation of washing soda from sodium chloride. List four industrial/domestic ​uses of washing soda.
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    Sodium chloride gives sodium hydrogencarbonate, heating gives sodium carbonate, and recrystallisation gives washing soda, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$.

    Step 1: sodium chloride (as brine) reacts with water, carbon dioxide and ammonia to give sodium hydrogencarbonate (baking soda): $\text{NaCl}+{\text{H}}_2\text{O}+{\text{CO}}_2+{\text{NH}}_3\to {\text{NH}}_4\text{Cl}+{\text{NaHCO}}_3$. Step 2: heating sodium hydrogencarbonate gives sodium carbonate: $2{\text{NaHCO}}_3\stackrel{\text{heat}}{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$. Step 3: recrystallising sodium carbonate from water gives washing soda: ${\text{Na}}_2{\text{CO}}_3+10{\text{H}}_2\text{O}\to {\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$. Uses of washing soda: (i) in the glass, soap and paper industries; (ii) in the manufacture of sodium compounds such as borax; (iii) as a cleaning agent for domestic purposes; (iv) for removing permanent hardness of water.

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12. Q232 CBSE 2024
    Name and ​explain ​the process used ​to obtain sodium ​hydroxide ​from the aqueous ​solution ​of sodium chloride (Brine). Name the two gases ​which are given at the anode and the cathode respectively. List two uses of each of these gases.
    Show answer

    Chlor-alkali process: chlorine at the anode and hydrogen at the cathode, with sodium hydroxide formed near the cathode.

    Process: the chlor-alkali process. When electricity is passed through brine it decomposes: $2\text{NaCl}(aq)+2{\text{H}}_2\text{O}(l)\to 2\text{NaOH}(aq)+{\text{Cl}}_2(g)+{\text{H}}_2(g)$. Chloride ions give up electrons at the anode (positive electrode); at the cathode (negative electrode) water gives hydrogen and leaves hydroxide ions, so sodium hydroxide solution forms near the cathode. Gas at the anode: chlorine. Gas at the cathode: hydrogen. Uses of chlorine: treating drinking water and swimming pools; making PVC, pesticides and bleaching powder. Uses of hydrogen: as a fuel; making margarine (hydrogenation of oils) and ammonia for fertilisers.

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13. Q233 CBSE 2024
    Salts ​play a very important role in our daily life. ​Sodium ​chloride which is known as common salt ​is used almost in every kitchen. Baking soda is also ​a ​salt used in faster ​cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions ​present in them.

    1. (a)Identify the acid and base from which Sodium chloride is formed.[1]
    2. (b)Find the cation and the anion present in Calcium sulphate.[1]
    3. (c)(i)“Sodium chloride and washing soda both belong to the same family of salts.” Justify this statement.[2]
    4. (c)(ii)OR : Define the term pH scale. Name the salt obtained by the reaction of Potassium hydroxide and Sulphuric acid and give the pH value of its aqueous solution.[2]
    Show answer

    $\text{HCl}$ and $\text{NaOH}$ form sodium chloride; calcium sulphate has ${\text{Ca}}^{2+}$ and ${\text{SO}}_4^{2-}$; sodium chloride and washing soda share ${\text{Na}}^{+}$.

    (a) Sodium chloride is formed from hydrochloric acid, $\text{HCl}$, and sodium hydroxide, $\text{NaOH}$: $\text{NaOH}+\text{HCl}\to \text{NaCl}+{\text{H}}_2\text{O}$. (b) Cation: calcium ion, ${\text{Ca}}^{2+}$; anion: sulphate ion, ${\text{SO}}_4^{2-}$. (c)(i) Salts having the same positive or the same negative ion belong to one family. Sodium chloride (${\text{Na}}^{+}$, ${\text{Cl}}^{-}$) and washing soda, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$ (${\text{Na}}^{+}$, ${\text{CO}}_3^{2-}$), have the same cation, ${\text{Na}}^{+}$, so both belong to the family of sodium salts. OR (c)(ii) The pH scale is a scale for measuring the hydrogen ion concentration in a solution, from 0 (very acidic) to 14 (very alkaline), with 7 as neutral. $2\text{KOH}+{\text{H}}_2{\text{SO}}_4\to {\text{K}}_2{\text{SO}}_4+2{\text{H}}_2\text{O}$: the salt is potassium sulphate. It is the salt of a strong acid and a strong base, so its aqueous solution is neutral, $\text{pH}=7$.

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14. Q234 CBSE 2023
    In the ​experimental setup given ​below, it is observed that on ​passing the gas produced ​in the reaction in the solution 'X' ​the solution 'X' first turns milky and then colourless. The option ​that justifies the above stated observation is that 'X' is aqueous calcium hydroxide ​and

    1. (a)it turns milky due to carbon dioxide gas liberated in the reaction and after sometime it becomes colourless due to formation of calcium carbonate.
    2. (b)it turns milky due to formation of calcium carbonate and on passing excess of carbon dioxide it becomes colourless due to formation of calcium hydrogen carbonate which is soluble in water.
    3. (c)it turns milky due to passing of carbon dioxide through it. It turns colourless as on further passing carbon dioxide, sodium hydrogen carbonate is formed which is soluble in water.
    4. (d)the carbon dioxide liberated during the reaction turns lime water milky due to formation of calcium hydrogen carbonate and after some time it turns colourless due to formation of calcium carbonate which is soluble in water.
    Show answer

    (b) it turns milky due to formation of calcium carbonate and on passing excess of carbon dioxide it becomes colourless due to formation of calcium hydrogen carbonate which is soluble in water.

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15. Q235 CBSE 2023
    When Sodium ​bicarbonate ​reacts with dilute ​hydrochloric ​acid, the ​gas evolved is ​:

    1. (a)Hydrogen; it gives pop sound with burning match stick.
    2. (b)Hydrogen; it turns lime water milky.
    3. (c)Carbon dioxide; it turns lime water milky.
    4. (d)Carbon dioxide; it blows off a burning match stick with a pop sound.
    Show answer

    (c) Carbon dioxide; it turns lime water milky.

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16. Q236 CBSE 2023
    Select a ​pair ​of ​olfactory ​indicators from the ​following :

    1. (a)Clove oil and vanilla essence
    2. (b)Onion and turmeric
    3. (c)Clove oil and litmus solution
    4. (d)Vanilla and methyl orange
    Show answer

    (a) Clove oil and vanilla essence

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17. Q237 CBSE 2023
    After burning ​a ​magnesium ribbon a student collected the ash so formed in a ​watch glass. He ​then dissolved this ​ash in water and tested the nature (acidic or basic) ​of ​the solution using pH paper and litmus solution. His correct observation ​would be :

    1. (a)Its pH is 10 and it turns blue litmus to red.
    2. (b)Its pH is 4 and it turns blue litmus to red.
    3. (c)Its pH is 4 and it turns red litmus to blue.
    4. (d)Its pH is 10 and it turns red litmus to blue.
    Show answer

    (d) Its pH is 10 and it turns red litmus to blue.

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18. Q238 CBSE 2023
    In the ​given ​experimental set-up, if the ​experiment ​is carried out separately with each ​of the ​following solutions the cases in ​which the bulb will glow is/are :

    1. (i)Dilute hydrochloric ​acid
    2. (ii)Dilute sulphuric acid
    3. (iii)Glucose solution
    4. (iv)Alcohol

    1. (a)(i) only
    2. (b)(ii) only
    3. (c)(i) and (ii)
    4. (d)(ii), (iii) and (iv)
    Show answer

    (c) (i) and (ii)

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19. Q239 CBSE 2023
    Few ​drops of aqueous solution of ammonium chloride are ​put on a universal indicator paper. The ​paper turns ​pink. Study the ​following table and ​choose the correct ​option.

    Nature, parent acid and base, and pH range of ammonium chloride solution

    Option	Nature	Ammonium chloride is a salt of ....	Range of pH
    (a)	acidic	weak acid and strong base	less than 7
    (b)	basic	weak acid and strong base	more than 7
    (c)	acidic	strong acid and weak base	less than 7
    (d)	basic	strong acid and strong base	7

    1. (a)Nature acidic; a salt of weak acid and strong base; pH less than $7$
    2. (b)Nature basic; a salt of weak acid and strong base; pH more than $7$
    3. (c)Nature acidic; a salt of strong acid and weak base; pH less than $7$
    4. (d)Nature basic; a salt of strong acid and strong base; pH $7$
    Show answer

    (c) Nature acidic; a salt of strong acid and weak base; pH less than $7$

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20. Q240 CBSE 2023
    The ​aqueous solution of ​which one of the ​following ​salts will ​have pH more than seven ?

    1. (a)${\text{NH}}_4\text{Cl}$
    2. (b)$\text{NaCl}$
    3. (c)${\text{Na}}_2{\text{CO}}_3$
    4. (d)${\text{NaNO}}_3$
    Show answer

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

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