Chapter 2 · Acids, Bases and Salts

NCERT Class 10 Science Chapter 2 Intext Questions (Page 28)

All 4 questions of NCERT Class 10 Science Chapter 2 Intext Questions (Page 28) — Acids, Bases and Salts — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   You have two ​solutions, A and B. The pH of solution ​A is $6$ and pH of solution B is $8$. ​Which solution has more hydrogen ion ​concentration? Which of this is ​acidic ​and ​which one is basic?
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   Solution A (pH $6$) has the higher hydrogen-ion concentration and is acidic; solution B (pH $8$) is basic.

   Solution A (pH $6$) has the higher hydrogen-ion concentration, because the lower the pH, the higher the concentration of ${\text{H}}^{+}$ ions. Solution A (pH $6$, less than $7$) is acidic and solution B (pH $8$, more than $7$) is basic.

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2. Q2
   What ​effect does ​the concentration of ${\text{H}}^{+}(aq)$ ​ions ​have ​on the nature of ​the ​solution?
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   The higher the ${\text{H}}^{+}(\text{aq})$ concentration, the more acidic the solution and the lower its pH.

   The concentration of ${\text{H}}^{+}(aq)$ ions decides how acidic a solution is. The higher the concentration of ${\text{H}}^{+}(aq)$ ions, the more acidic (the stronger) the solution and the lower its pH; the lower the concentration of ${\text{H}}^{+}(aq)$ ions, the less acidic the solution and the higher its pH. When the ${\text{H}}^{+}$ and ${\text{OH}}^{-}$ concentrations are equal the solution is neutral (pH $7$), and when ${\text{OH}}^{-}$ ions are in excess it is basic (pH above $7$).

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3. Q3
   Do basic solutions ​also ​have ${\text{H}}^{+}(aq)$ ions? If ​yes, ​then why ​are ​these basic?
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   Yes; basic solutions contain some ${\text{H}}^{+}$ from water, but they are basic because ${\text{OH}}^{-}$ ions far outnumber ${\text{H}}^{+}$ ions.

   Yes. Basic solutions also contain ${\text{H}}^{+}(aq)$ ions, because water itself ionises to a very small extent: ${\text{H}}_2\text{O}(l)\rightleftharpoons {\text{H}}^{+}(aq)+{\text{OH}}^{-}(aq)$. They are basic because the concentration of ${\text{OH}}^{-}(aq)$ ions in them is much greater than the concentration of ${\text{H}}^{+}(aq)$ ions; this excess of hydroxide ions gives the solution its basic nature (pH above $7$).

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4. Q4
   Under what soil ​condition do you ​think a farmer would ​treat the soil of his ​fields with quick ​lime ​(calcium oxide) or slaked ​lime (calcium hydroxide) or ​chalk (calcium carbonate)?
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   A farmer treats acidic soil (pH below $7$) with quick lime, slaked lime or chalk, which neutralise the excess acid.

   When the soil is acidic — its pH is below $7$, too low for the healthy growth of plants. Quick lime ($\text{CaO}$) and slaked lime (${\text{Ca(OH)}}_2$) are bases and chalk (${\text{CaCO}}_3$) is a basic salt; each neutralises the excess acid in the soil and raises its pH towards the range the crops need.

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