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CBSE Class 10 Science 2023 Outside Delhi Set 1

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Question : 28 of 39
Marks: +1, -0
(a) A substance ' XX ' is used as a building material and is insoluble in water. When it reacts with dil. HCl\mathrm{HCl}, it produces a gas which turns lime water milky.
(i) Write the chemical name and formula of ' XX '.
(ii) Write chemical equations for the chemical reactions involved in the above statements.
OR
(b) A metal ' MM ' on reacting with dilute acid liberates a gas ' GG '. The same metal also liberates gas ' GG ' when reacts with a base.
(i) Write the name of gas ' GG '
(ii) How will you test the presence of this gas?
(iii) Write chemical equations for the reactions of the metal with (1) an acid and (2) a base.
Solution:  
(a) (i) Substance XX is Calcium Carbonate (CaCO3)(\mathrm{CaCO}_3) or limestone.
(ii)
CaCO3(s)Calcium carbonate  (X)+2 HCl(aq)dil→CaCl2(aq)Calcium chloride+H2O(l)+CO2↑\underset{\text{Calcium carbonate}\; (X)}{\mathrm{CaCO}_3(s)} + \underset{dil}{2\,\mathrm{HCl}(aq)} \rightarrow \underset{\text{Calcium chloride}}{\mathrm{CaCl}_2(aq)} + \mathrm{H}_2\mathrm{O}(l) + \mathrm{CO}_2\uparrow
Carbon dioxide gas (CO2)(\mathrm{CO}_2) evolved turns lime water milky.
CO2+Ca(OH)2(aq)  (lime water)  →CaCO3(s)  milky  +H2O(l)\mathrm{CO}_2 + \underset{\;\text{(lime water)}\;}{\mathrm{Ca(OH)}_2(aq)} \rightarrow \underset{\;\text{milky}\;}{\mathrm{CaCO}_3(s)} + \mathrm{H}_2\mathrm{O}(l)
(b) (i) The gas GG is hydrogen gas.
(ii) A characteristic test for hydrogen (H2)(\mathrm{H}_2) gas can be performed by bringing a burning candle near the source of hydrogen. On doing so, hydrogen gas burns with a squeaky pop sound.
Hydrogen gas is recognised by the 'pop' when it burns. The 'pop' is the sound of a small explosion.
(iii) Zinc metal, reacts with both acid and base to produce hydrogen gas.
Zn(s)Zinc+2 NaOH(aq)  Sodium hydroxide  →  Heat  Na2ZnO2(aq)+H2(g)↑Hydrogen  Sodium zincate  \underset{\text{Zinc}}{\mathrm{Zn}(s)} + \underset{\;\text{Sodium hydroxide}\;}{2\,\mathrm{NaOH}(aq)} \xrightarrow{\;\text{Heat}\;} \underset{\;\text{Sodium zincate}\;}{\mathrm{Na}_2\mathrm{ZnO}_2(aq) + \underset{\text{Hydrogen}}{\mathrm{H}_2(g)\uparrow}}
Zn(s)+2 HCl(aq)Hydrochloric acid(dil.)→ZnCl2(aq)+H2(g)↑Zinc chloride\underset{\text{Hydrochloric acid(dil.)}}{\mathrm{Zn}(s) + 2\,\mathrm{HCl}(aq)} \rightarrow \underset{\text{Zinc chloride}}{\mathrm{ZnCl}_2(aq) + \mathrm{H}_2(g)\uparrow}
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