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NCERT Exemplar · Class 10 Science Acids, Bases and Salts

48 questions · 48 still being checked

Multiple Choice Questions 11–20 (part 2 of 5)

  1. Exercise 11

    Common salt besides being used in kitchen can also be used as the raw material for making
    (i)
    washing soda
    (ii)
    bleaching powder
    (iii)
    baking soda
    (iv)
    slaked lime
    (a) (i) and (ii)
    (b) (i), (ii) and (iv)
    (c) (i) and (iii)
    (d) (i), (iii) and (iv)

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    NCERT’s answer
    (c)
    (c) (i) and (iii). Both sodium salts form directly from \(\displaystyle \mathrm{NaCl}\); slaked lime comes from limestone, and bleaching powder uses salt only indirectly, through \(\displaystyle \mathrm{Cl_2}\). \[\mathrm{NaCl + NH_3 + CO_2 + H_2O \rightarrow NaHCO_3\downarrow + NH_4Cl} \] \[\mathrm{2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2\uparrow} \] \[\mathrm{Na_2CO_3 + 10H_2O \rightarrow Na_2CO_3\cdot 10H_2O} \]

  2. Exercise 12

    One of the constituents of baking powder is sodium hydrogencarbonate, the other constituent is
    (a)
    hydrochloric acid
    (b)
    tartaric acid
    (c)
    acetic acid
    (d)
    sulphuric acid

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    NCERT’s answer
    (b)
    (b) Tartaric acid. It supplies the \(\displaystyle \mathrm{H^+}\) that reacts with sodium hydrogencarbonate on wetting, releasing the leavening gas. \[\mathrm{2NaHCO_3 + C_4H_6O_6 \rightarrow Na_2C_4H_4O_6 + 2H_2O + 2CO_2\uparrow} \]

  3. Exercise 13

    To protect tooth decay we are advised to brush our teeth regularly. The nature of the tooth paste commonly used is
    (a)
    acidic
    (b)
    neutral
    (c)
    basic
    (d)
    corrosive

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    NCERT’s answer
    (c)
    (c) Basic. Bacteria turn sugar residue on teeth acidic, and enamel starts dissolving once the mouth's pH drops: \[\mathrm{pH_{mouth}\downarrow \;(<5.5)\; \Rightarrow\; enamel\ decay} \] A basic paste neutralises that acid before it can attack the enamel.

  4. Exercise 14

    Which of the following statements is correct about an aqueous solution of an acid and of a base?
    (i)
    Higher the pH, stronger the acid
    (ii)
    Higher the pH, weaker the acid
    (iii)
    Lower the pH, stronger the base
    (iv)
    Lower the pH, weaker the base
    (a) (i) and (iii)
    (b) (ii) and (iii)
    (c) (i) and (iv)
    (d) (ii) and (iv)

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    NCERT’s answer
    (d)
    (d) (ii) and (iv). Moving away from pH $\displaystyle 7$ means a stronger solution, so weaker means the pH sits closer to neutral on each side: \[\mathrm{acid:\ pH\uparrow \Rightarrow [H^+]\downarrow \Rightarrow strength\downarrow} \] \[\mathrm{base:\ pH\downarrow \Rightarrow [OH^-]\downarrow \Rightarrow strength\downarrow} \]

  5. Exercise 15

    The pH of the gastric juices released during digestion is
    (a)
    less than 7\displaystyle 7
    (b)
    more than 7\displaystyle 7
    (c)
    equal to 7\displaystyle 7
    (d)
    equal to 0\displaystyle 0

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    NCERT’s answer
    (a)
    (a) Less than 7. Gastric glands secrete hydrochloric acid (pH about $\displaystyle 1.5$-$\displaystyle 3.5$) that activates pepsin and kills swallowed bacteria.

  6. Exercise 16

    Which of the following phenomena occur, when a small amount of acid is added to water?
    (i)
    Ionisation
    (ii)
    Neutralisation
    (iii)
    Dilution
    (iv)
    Salt formation
    (a) (i) and (ii)
    (b) (i) and (iii)
    (c) (ii) and (iii)
    (d) (ii) and (iv)

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    NCERT’s answer
    (b)
    (b) (i) and (iii). The acid ionises in water and the added water simply spreads those ions through a larger volume: \[\mathrm{HA + H_2O \rightarrow H_3O^+ + A^-} \] No base is present, so neither neutralisation nor any salt forms.

  7. Exercise 17

    Which one of the following can be used as an acid–base indicator by a visually impared student?
    (a)
    Litmus
    (b)
    Turmeric
    (c)
    Vanilla essence
    (d)
    Petunia leaves

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    NCERT’s answer
    (c)
    (c) Vanilla essence.Olfactory indicators change odour, not colour, in acid or base -- vanilla essence loses its scent in a basic medium, so a visually impaired student senses that without seeing any colour change.

  8. Exercise 18

    Which of the following substance will not give carbon dioxide on treatment with dilute acid?
    (a)
    Marble
    (b)
    Limestone
    (c)
    Baking soda
    (d)
    Lime

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    NCERT’s answer
    (d)
    (d) Lime.\[\mathrm{CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2\uparrow} \quad \text{(marble, limestone)} \] \[\mathrm{NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2\uparrow} \quad \text{(baking soda)} \] \[\mathrm{CaO + 2HCl \rightarrow CaCl_2 + H_2O} \] Lime is an oxide, not a carbonate, so no \(\displaystyle \mathrm{CO_2}\) forms.

  9. Exercise 19

    Which of the following is acidic in nature?
    (a)
    Lime juice
    (b)
    Human blood
    (c)
    Lime water
    (d)
    Antacid

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    NCERT’s answer
    (a)
    (a) Lime juice.Citric acid puts it at \(\displaystyle \mathrm{pH} < 7\); human blood is \(\displaystyle \approx 7.4\), and lime water and antacids are basic (\(\displaystyle \mathrm{pH} > 7\)).

  10. Exercise 20

    In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus (Figure 2.1\displaystyle 2.1) was set up.
    Which among the following statement(s) is(are) correct?
    (i)
    Bulb will not glow because electrolyte is not acidic
    (ii)
    Bulb will glow because NaOH is a strong base and furnishes ions for conduction.
    (iii)
    Bulb will not glow because circuit is incomplete
    (iv)
    Bulb will not glow because it depends upon the type of electrolytic solution
    (a) (i) and (iii)
    (b) (ii) and (iv)
    (c) (ii) only
    (d) (iv) only
    NCERT_Question_Class10_Science_Exemplar_Ch2_Q20

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    NCERT’s answer
    (c)
    (c) (ii) only.The circuit is closed: battery, bulb and switch connect through the two nail electrodes into the dilute \(\displaystyle \mathrm{NaOH}\) solution. \[\mathrm{NaOH \rightarrow Na^+ + OH^-} \] A strong base furnishes free ions, so current flows and the bulb glows.