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Question 14 Marks
Starting from carbon dioxide how would you obtain $(a)$ A weak acid $(b)$ A fertilizer $(c)$ A highly poisonous gas $(d)$ Black particles of carbon. $[$Give balanced equations for the same$]$
Answer
$(a)$ Carbonic acid from $\ce{CO_2}$ : when $\ce{CO_2}$ is dissolved in water, carbonic acid is formed.
$\ce{CO_2+ H_2O} \longrightarrow \underset{\text { Carbonic acid }}{\ce{H_2CO_3}}$
$(b) \ \ce{CO_2}$ reacts with ammonia gas to form urea $($a nitrogenous fertilizers$)$.
$\underset{\text { Ammonia }}{\ce{2NH_3} + CO_2} \longrightarrow \underset{\text { Urea [fertilizer] }}{\left[\ce{NH _2}\right]_\ce{2CO } + H_2O}$
$(c)\ \ce{CO_2}$ is reduced to a highly poisonous gas $CO$ by carbon $($coke$)$.
$\ce{CO_2+ C} \longrightarrow \underset{\text{Carbon monoxide gas}}{\ce{2CO}}$
$(d)$ Black particles of carbon : Burning magnesium bums in $\ce{CO_2}$ making use of oxygen of $\ce{CO_2}$ producing black carbon particles.
$\ce{2Mg + CO_2 \rightarrow 2 Mgo + C}$
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Question 24 Marks
In the laboratory preparation of carbon dioxide by action of a dilute acid on a metallic carbonate give $- (a)$ A balanced equation for the preparation $(b)$ A reason for $(i)$ use of a washer bottle containing cone. $\ce{H_2SO_4}$ in the preparation $(ii)$ Not collecting the prepared gas over water $(iii)$ Not using dilute sulphuric acid as a reactant in the preparation.
Answer
$(a) \ce{CaCO_3 + 2 HCl \rightarrow CaCl _2 + CO_2 + H_2O}$
$(b) (i)$ Cone. $\ce{H_2SO_4}$ used in washer bottle absorbs moisture from the gas.
$(ii) \ce{CO_2}$ is soluble in water and hence is not collected over water.
$(iii)$ Dil. sulphuric acid is not used as reactant. Since $\ce{H_2SO_4}$ reacts with calcium carbonate forming a coating of insoluble calcium sulphate $\left[ CaSO _4\right]$. The reaction slowly comes to a stop.
$\ce{CaCO_3 + H_2SO_4} \text { (dil.) } \rightarrow \ce{CaSO_4} \text { (Insoluble) } + \ce{H_2O + CO_2}$
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[5 Mark Question Answer] - CHEMISTRY STD 8 Questions - Vidyadip