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NCERT Exemplar · Class 10 Science Acids, Bases and Salts

48 questions · 48 still being checked

Short Answer Questions 31–42 (part 4 of 5)

  1. Exercise 31

    Match the acids given in Column (A) with their correct source given in Column (B)
    Column (A)Column (B)
    (a) Lactic acid(i) Tomato
    (b) Acetic acid(ii) Lemon
    (c) Citric acid(iii) Vinegar
    (d) Oxalic acid(iv) Curd

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    NCERT’s answer
    (a)
    — (iv)
    (b)
    — (iii)
    (c)
    — (ii)
    (a)
    Lactic acid is present in curd. (b) Acetic acid is present in vinegar. (c) Citric acid is present in lemon. (d) Oxalic acid is present in tomato.
    Answer: (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

  2. Exercise 32

    Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)
    Column (A)Column (B)
    (a) Plaster of Paris(i) Ca(OH)2\displaystyle \mathrm{Ca}(\mathrm{OH})_2
    (b) Gypsum(ii) CaSO4⋅1/2H2O\displaystyle \mathrm{CaSO}_4 \cdot 1 / 2 \mathrm{H}_2 \mathrm{O}
    (c) Bleaching Powder(iii) CaSO4⋅2H2O\displaystyle \mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}
    (d) Slaked Lime(iv) Ca(ClO)2\displaystyle \mathrm{Ca}(\mathrm{ClO})_2

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    NCERT’s answer
    (a)
    — (ii)
    (b)
    — (iii)
    (c)
    — (iv)
    (a)
    Plaster of Paris is \(\displaystyle \mathrm{CaSO_4 \cdot \tfrac{1}{2}H_2O}\). (b) Gypsum is \(\displaystyle \mathrm{CaSO_4 \cdot 2H_2O}\). (c) Bleaching powder is \(\displaystyle \mathrm{Ca(ClO)_2}\). (d) Slaked lime is \(\displaystyle \mathrm{Ca(OH)_2}\).
    Answer: (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)

  3. Exercise 33

    What will be the action of the following substances on litmus paper? Dry HCl gas, Moistened NH3\displaystyle \mathrm{NH}_3 gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.

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    NCERT’s answer
    SubstanceAction on Litmus paper
    Dry HCl gasNo change
    Moistened \(\displaystyle \mathrm{NH}_3\) gasTurns red to blue
    Lemon juiceTurns blue to red
    Carbonated soft drinkTurns blue to red
    CurdTurns blue to red
    Soap solutionTurns red to blue
    \[\mathrm{NH_3(g)} + \mathrm{H_2O(l)} \rightarrow \mathrm{NH_4^+(aq)} + \mathrm{OH^-(aq)} \] Moist \(\displaystyle \mathrm{NH_3}\) and soap solution are basic (\(\displaystyle \mathrm{OH^-}\) as above): red litmus \(\displaystyle \rightarrow\) blue. Lemon juice, soft drink and curd are acidic (\(\displaystyle \mathrm{H^+}\)): blue litmus \(\displaystyle \rightarrow\) red. Dry HCl gas has no water to ionise, so dry litmus shows no change.Answer: Blue\(\displaystyle \to\)red: lemon juice, soft drink, curd. Red\(\displaystyle \to\)blue: moist \(\displaystyle \mathrm{NH_3}\), soap solution. No change: dry HCl gas.

  4. Exercise 34

    Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

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    NCERT’s answer
    The acid present in 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 \(\displaystyle \left(\mathrm{NaHCO}_3\right)\) on it.
    Ant sting contains formic (methanoic) acid, \(\displaystyle \mathrm{HCOOH}\). Rubbing on a mild base such as baking soda (\(\displaystyle \mathrm{NaHCO_3}\)) neutralises it: \[\mathrm{HCOOH(aq)} + \mathrm{NaHCO_3(aq)} \rightarrow \mathrm{HCOONa(aq)} + \mathrm{H_2O(l)} + \mathrm{CO_2(g)} \]Answer: Formic acid, \(\displaystyle \mathrm{HCOOH}\); relief by applying baking-soda paste to neutralise it.

  5. Exercise 35

    What happens when nitric acid is added to egg shell?

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    NCERT’s answer
    Egg shells contain calcium carbonate. When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as \[\mathrm{CaCO}_3+2 \mathrm{HNO}_3 \rightarrow \mathrm{Ca}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \]
    Egg shell is \(\displaystyle \mathrm{CaCO_3}\); nitric acid reacts with it: \[\mathrm{CaCO_3(s)} + 2\mathrm{HNO_3(aq)} \rightarrow \mathrm{Ca(NO_3)_2(aq)} + \mathrm{H_2O(l)} + \mathrm{CO_2(g)} \] Brisk effervescence is seen as \(\displaystyle \mathrm{CO_2}\) gas escapes.Answer: Vigorous bubbling; \(\displaystyle \mathrm{CO_2}\) gas is released, leaving calcium nitrate solution.

  6. Exercise 36

    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?

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    NCERT’s answer
    Hint— Using chemical indicator like phenolphthalein or natural indicators like turmeric, china rose etc.
    With no litmus, use a natural indicator such as turmeric paper: \(\displaystyle \text{base} + \text{turmeric (yellow)} \Rightarrow \text{reddish-brown}\); the acid leaves it unchanged, yellow.Answer: Dip turmeric paper in each: the solution turning reddish-brown is the base, the one staying yellow is the acid.

  7. Exercise 37

    How would you distinguish between baking powder and washing soda by heating?

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    NCERT’s answer
    The chemical formula of baking powder is sodium hydrogencarbonate \(\displaystyle \left(\mathrm{NaHCO}_3\right)\). Whereas, that of washing soda is sodium carbonate (\(\displaystyle \mathrm{Na}_2 \mathrm{CO}_3 .10 \mathrm{H}_2 \mathrm{O}\)) Sodium hydrogencarbonate on heating gives \(\displaystyle \mathrm{CO}_2\) gas which will turn lime water milky whereas no such gas is obtained from sodium carbonate. \[\begin{aligned} & 2 \mathrm{NaHCO}_3 \xrightarrow{\text { Heat }} \mathrm{Na}_2 \mathrm{CO}_3+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \\ & \mathrm{Na}_2 \mathrm{CO}_3 .10 \mathrm{H}_2 \mathrm{O} \xrightarrow{\text { Heat }} \mathrm{Na}_2 \mathrm{CO}_3+10 \mathrm{H}_2 \mathrm{O} \end{aligned} \]
    Heat each separately and pass the gas evolved into lime water. \[2\,\mathrm{NaHCO_3(s)} \xrightarrow{\Delta} \mathrm{Na_2CO_3(s)} + \mathrm{H_2O(g)} + \mathrm{CO_2(g)}\uparrow \] \[\mathrm{CO_2} + \mathrm{Ca(OH)_2} \rightarrow \mathrm{CaCO_3}\downarrow + \mathrm{H_2O} \] Baking powder's \(\displaystyle \mathrm{NaHCO_3}\) gives this \(\displaystyle \mathrm{CO_2}\); lime water turns milky. \[\mathrm{Na_2CO_3\cdot10H_2O(s)} \xrightarrow{\Delta} \mathrm{Na_2CO_3(s)} + 10\,\mathrm{H_2O(g)}\uparrow \] Washing soda only loses water of crystallisation — the vapour does not turn lime water milky.

  8. Exercise 38

    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 C.

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    NCERT’s answer
    Baking powder \(\displaystyle \left(\mathrm{NaHCO}_3\right)\), salt A is commonly used in bakery products. On heating it forms sodium carbonate \(\displaystyle \left(\mathrm{Na}_2 \mathrm{CO}_3\right)\), B and \(\displaystyle \mathrm{CO}_2\) gas, C is evolved. When \(\displaystyle \mathrm{CO}_2\) gas is passed through lime water it forms calcium carbonate \(\displaystyle \left(\mathrm{CaCO}_3\right)\), which is slightly soluble in water making it milky. A — \(\displaystyle \mathrm{NaHCO}_3\) B — \(\displaystyle \mathrm{Na}_2 \mathrm{CO}_3\) C — \(\displaystyle \mathrm{CO}_2\) gas
    \[2\,\underbrace{\mathrm{NaHCO_3}}_{A} \xrightarrow{\Delta} \underbrace{\mathrm{Na_2CO_3}}_{B} + \mathrm{H_2O} + \underbrace{\mathrm{CO_2}}_{C}\uparrow \] Gas \(\displaystyle C\) turns lime water milky: \[\mathrm{CO_2} + \mathrm{Ca(OH)_2} \rightarrow \mathrm{CaCO_3}\downarrow + \mathrm{H_2O} \]

  9. Exercise 39

    In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved.

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    NCERT’s answer
    In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by–products. When chlorine gas (X) reacts with lime water, it forms bleaching powder Y. The reactions are \[\begin{aligned} & 2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g}) \\ & \mathrm{X} \rightarrow \mathrm{Cl}_2(\mathrm{Chlorine} \text { gas }) \\ & 2 \mathrm{Ca}(\mathrm{OH})_2+2 \mathrm{Cl}_2 \rightarrow \mathrm{Ca}(\mathrm{ClO})_2+\mathrm{CaCl}_2+2 \mathrm{H}_2 \mathrm{O} \end{aligned} \] Y — bleaching powder
    Chlor-alkali electrolysis of brine: \[2\,\mathrm{NaCl(aq)} + 2\,\mathrm{H_2O(l)} \xrightarrow{\text{electrolysis}} 2\,\mathrm{NaOH(aq)} + \mathrm{Cl_2(g)}\uparrow + \mathrm{H_2(g)}\uparrow \] Gas \(\displaystyle X = \mathrm{Cl_2}\), passed into lime water: \[\mathrm{Cl_2} + \mathrm{Ca(OH)_2} \rightarrow \mathrm{CaOCl_2} + \mathrm{H_2O} \] giving the bleaching agent \(\displaystyle Y = \mathrm{CaOCl_2}\).

  10. Exercise 40

    Fill in the missing data in the following table
    Name of the saltFormulaSalt obtained from
    BaseAcid
    (i) Ammonium chlorideNH4Cl\displaystyle \mathrm{NH}_4 \mathrm{Cl}NH4OH\displaystyle \mathrm{NH}_4 \mathrm{OH}—
    (ii) Copper sulphate——H2SO4\displaystyle \mathrm{H}_2 \mathrm{SO}_4
    (iii) Sodium chlorideNaClNaOH—
    (iv) Magnesium nitrateMg(NO3)2\displaystyle \mathrm{Mg}\left(\mathrm{NO}_3\right)_2—HNO3\displaystyle \mathrm{HNO}_3
    (v) Potassium sulphateK2SO4\displaystyle \mathrm{K}_2 \mathrm{SO}_4——
    (vi) Calcium nitrateCa(NO3)2\displaystyle \mathrm{Ca}\left(\mathrm{NO}_3\right)_2Ca(OH)2\displaystyle \mathrm{Ca}(\mathrm{OH})_2—

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    NCERT’s answer
    Name of the saltFormulaSalt obtained from
    BaseAcid
    (i) Ammonium chloride\(\displaystyle \mathrm{NH}_4 \mathrm{Cl}\)\(\displaystyle \mathrm{NH}_4 \mathrm{OH}\)\(\displaystyle \underline{\mathrm{HCl}}\)
    (ii) Copper sulphate\(\displaystyle \underline{\mathrm{CuSO}_4}\)\(\displaystyle \underline{\mathrm{Cu}(\mathrm{OH})_2}\)\(\displaystyle \mathrm{H}_2 \mathrm{SO}_4\)
    (iii) Sodium chlorideNaClNaOH\(\displaystyle \underline{\mathrm{HCl}}\)
    (iv) Magnesium nitrate\(\displaystyle \mathrm{Mg}\left(\mathrm{NO}_3\right)_2\)\(\displaystyle \underline{\mathrm{Mg}(\mathrm{OH})_2}\)\(\displaystyle \mathrm{HNO}_3\)
    (v) Potassium sulphate\(\displaystyle \mathrm{K}_2 \mathrm{SO}_4\)\(\displaystyle \underline{\mathrm{KOH}}\)\(\displaystyle \underline{\mathrm{H}_2 \mathrm{SO}_4}\)
    (vi) Calcium nitrate\(\displaystyle \mathrm{Ca}\left(\mathrm{NO}_3\right)_2\)\(\displaystyle \mathrm{Ca}(\mathrm{OH})_2\)\(\displaystyle \underline{\mathrm{HNO}_3}\)
    Each blank follows from the salt's own formula and its parent base/acid pair: \[\begin{array}{|l|l|l|l|} \hline \text{Salt} & \text{Formula} & \text{Base} & \text{Acid} \\ \hline \text{Ammonium chloride} & \mathrm{NH_4Cl} & \mathrm{NH_4OH} & \mathbf{\mathrm{HCl}} \\ \hline \text{Copper sulphate} & \mathbf{\mathrm{CuSO_4}} & \mathbf{\mathrm{Cu(OH)_2}} & \mathrm{H_2SO_4} \\ \hline \text{Sodium chloride} & \mathrm{NaCl} & \mathrm{NaOH} & \mathbf{\mathrm{HCl}} \\ \hline \text{Magnesium nitrate} & \mathrm{Mg(NO_3)_2} & \mathbf{\mathrm{Mg(OH)_2}} & \mathrm{HNO_3} \\ \hline \text{Potassium sulphate} & \mathrm{K_2SO_4} & \mathbf{\mathrm{KOH}} & \mathbf{\mathrm{H_2SO_4}} \\ \hline \text{Calcium nitrate} & \mathrm{Ca(NO_3)_2} & \mathrm{Ca(OH)_2} & \mathbf{\mathrm{HNO_3}} \\ \hline \end{array} \]

  11. Exercise 41

    What are strong and weak acids? In the following list of acids, separate strong acids from weak acids. Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.

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    NCERT’s answer
    In aqueous solutions strong acids ionise completely and provide 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 \(\displaystyle \mathrm{H}_3 \mathrm{O}^{+}\) ions. Strong acids — Hydrochloric acid, sulphuric acid, nitric acid Weak acid — Citric acid, acetic acid , formic acid
    Strong acids ionise almost completely in water; weak acids ionise only partially, an equilibrium. \[\mathrm{HCl(aq)} \rightarrow \mathrm{H^+(aq)} + \mathrm{Cl^-(aq)} \quad \text{(complete)} \] \[\mathrm{CH_3COOH(aq)} \rightleftharpoons \mathrm{H^+(aq)} + \mathrm{CH_3COO^-(aq)} \quad \text{(partial)} \] Strong: hydrochloric acid, nitric acid, sulphuric acid. Weak: citric acid, acetic acid, formic acid.

  12. Exercise 42

    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 involved and also write a test to detect the gas formed.

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    NCERT’s answer
    When zinc reacts with dilute solution of strong acid, it forms salt and hydrogen gas is evolved. \[\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_2+\mathrm{H}_2 \] When a burning splinter is brought near the mouth of the test tube, the gas burns with a pop sound.
    \[\mathrm{Zn(s)} + \mathrm{H_2SO_4(aq)\,(dil.)} \rightarrow \mathrm{ZnSO_4(aq)} + \mathrm{H_2(g)}\uparrow \] The gas is hydrogen, used to hydrogenate oil (with Ni catalyst) into vanaspati ghee.Test: hold a burning splinter at the mouth of the tube — the gas burns with a pop sound. Caution: keep the tube's mouth turned away from your face before testing; the pop is a small explosion.