CBSE Class 10 Science 2023 Outside Delhi Set 1

Question : 28 of 39

Marks: +1, -0

(a) A substance '

{\X}

' is used as a building material and is insoluble in water. When it reacts with dil.

{\HCl}

, it produces a gas which turns lime water milky.
(i) Write the chemical name and formula of '

{\X}

'.
(ii) Write chemical equations for the chemical reactions involved in the above statements.
OR
(b) A metal '

M

' on reacting with dilute acid liberates a gas '

G

'. The same metal also liberates gas '

G

' when reacts with a base.
(i) Write the name of gas '

G

'
(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

{\X}

is Calcium Carbonate

( {\CaCO}_3)

or limestone.
(ii)

{{\CaCO}_3(s)}↙{\text "Calcium carbonate"\; (\X) }+{2 {\HCl}(\aq) }↙{\dil}→ { {\CaCl}_2(\aq)}↙{\text "Calcium chloride"} + {\H}_2 {\O}(l)+ {\CO}_2 ↑

Carbon dioxide gas

( {\CO}_2)

evolved turns lime water milky.

\;{ {\CO}_2}+\;{ {\Ca}( {\OH})_2(a q)}↙{\;\text " (lime water) "\;}→{{ {\CaCO}_3(s)}}↙{\;\text " milky "\;} +\;{{ {\H}_2 {\O}} (l)}

(b) (i) The gas

{\G}

is hydrogen gas.
(ii) A characteristic test for hydrogen

( {\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}(a q)} ↙{\;\text " Sodium hydroxide " } {→}↖{\;\text " Heat "\;} \;{ {\Na_2\ZnO_2(\aq)}↙{\;\text " Sodium zincate"}+ {{\H}_2(g) ↑}↙{\Hydrogen}

{\Zn(s)+2 \HCl(\aq) }↙{\text "Hydrochloric acid(dil.) "}→ {\ZnCl_2(\aq)+\H_2(g)↑ }↙{\text " Zinc chloride"}

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