Chapter 2 · Acids, Bases and Salts

NCERT Class 10 Science Chapter 2 Intext Questions (Page 33)

All 5 questions of NCERT Class 10 Science Chapter 2 Intext Questions (Page 33) — Acids, Bases and Salts — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   What ​is ​the common ​name ​of ​the ​compound ${\text{Ca(ClO)}}_2$?
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   The common name of ${\text{Ca(ClO)}}_2$ is bleaching powder.

   Bleaching powder. ${\text{Ca(ClO)}}_2$ is calcium oxychloride (calcium hypochlorite), the compound obtained by the action of chlorine on dry slaked lime, ${\text{Ca(OH)}}_2$, and known commonly as bleaching powder.

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2. Q2
   Name the ​substance which ​on ​treatment ​with ​chlorine yields bleaching powder.
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   Dry slaked lime, calcium hydroxide, which gives bleaching powder on treatment with chlorine.

   Dry slaked lime, that is calcium hydroxide, ${\text{Ca(OH)}}_2$. On treatment with chlorine it yields bleaching powder: $2{\text{Ca(OH)}}_2+2{\text{Cl}}_2\to {\text{Ca(ClO)}}_2+{\text{CaCl}}_2+2{\text{H}}_2\text{O}$.

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3. Q3
   Name the ​sodium compound which ​is ​used ​for ​softening hard ​water.
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   Washing soda (sodium carbonate), which removes hardness by precipitating calcium and magnesium salts as insoluble carbonates.

   Washing soda — sodium carbonate, ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$. It removes the permanent hardness of water by precipitating the dissolved calcium and magnesium salts as insoluble carbonates, for example ${\text{CaCl}}_2(aq)+{\text{Na}}_2{\text{CO}}_3(aq)\to {\text{CaCO}}_3(s)+2\text{NaCl}(aq)$.

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4. Q4
   What ​will happen if a solution ​of sodium hydrocarbonate ​is heated? Give the ​equation of ​the ​reaction involved.
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   Sodium hydrogencarbonate decomposes on heating, giving carbon dioxide, water and sodium carbonate: $2{\text{NaHCO}}_3\to {\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$.

   On heating, the sodium hydrogencarbonate (baking soda, ${\text{NaHCO}}_3$; printed as 'sodium hydrocarbonate') decomposes: carbon dioxide gas is given off with effervescence, water is formed and sodium carbonate is left in the solution. Equation: $2{\text{NaHCO}}_3\stackrel{\text{heat}}{\to }{\text{Na}}_2{\text{CO}}_3+{\text{H}}_2\text{O}+{\text{CO}}_2$. It is a thermal decomposition reaction; the gas turns lime water milky.

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5. Q5
   Write ​an ​equation ​to show the ​reaction ​between ​Plaster of Paris ​and water.
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   Plaster of Paris takes up water and sets to gypsum: ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$.

   ${\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O}+1\frac{1}{2}{\text{H}}_2\text{O}\to {\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O}$ — Plaster of Paris (calcium sulphate hemihydrate) takes up $1\frac{1}{2}$ molecules of water per ${\text{CaSO}}_4$ and sets to gypsum (calcium sulphate dihydrate), a hard solid mass. In whole numbers: $2({\text{CaSO}}_4\cdot \frac{1}{2}{\text{H}}_2\text{O})+3{\text{H}}_2\text{O}\to 2({\text{CaSO}}_4\cdot 2{\text{H}}_2\text{O})$.

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