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MODEL PAPER 10 — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceMODEL PAPER 103 Marks
Question
$i.$ Distinguish between ionic and covalent compounds under the following properties:
$a.$ Strength of forces between constituent elements
$b.$ Solubility of compounds in water
$c.$ Electrical conduction in substances
$ii.$ Explain how the following metals are obtained from their compounds by the reduction process:
$a.$ Metal $M$ which is in the middle of the reactivity series.
$b.$ Metal $N$ which is high up in the reactivity series. Give one example of each type.
✓

Answer

$i$. a. Ionic compounds have strong force of attraction between the oppositely charged ions $($e.g., $Na ^{+}$and $Cl ^{-}),$ so they are solids.
Covalent compounds have weak force of attraction between their molecules, so they are usually liquids or gases.
$b$. Ionic compounds are soluble in water but covalent compounds are insoluble in water.
$c$. Ionic compounds conduct electricity when dissolved in water or when melted because they contain ions $($charged particles$)$. But, covalent compounds like glucose do not conduct electricity because they do not contain ions.
$ii$. a. The metal M which is in the middle of the reactivity series $($such as iron, zinc, lead, copper, etc.$)$ is moderately reactive.
So, for obtaining such metals from their compounds, their sulphides and carbonates $($in which they are present in nature$)$ are first converted into their oxides by the process of roasting and calcination respectively. For example,
$\underset{\substack{\text { Zinc Sulphide }$
$\text { (Sulphideore) }}}{2 \ce{ZnS ( s )}+3 O _2(g)} \xrightarrow{\text { Heat }} \ce{2 ZnO ( s )+2 SO _2(g)}$
$\underset{\substack{\text { Zinc Carbonate }$
$\text { (Carbonate are) }}}{ \ce{ZnCO _3(s)}} \xrightarrow{\text { Heat }} \ce{ZnO ( s )+ CO _2(g)}$
The metal oxide $(MO)$ are then reduced to the corresponding metals by using suitable reducing agents such as carbon. For example, zinc metal from its oxide is obtained as follow:
$\underset{\text { Zinc oxide }}{ \ce{ZnO (s)}+C(s)} \rightarrow \underset{\text { Zinc }}{ \ce{Zn (s)}}+ \ce{CO ( g )}$
$b$. The metal N which is high up in the reactivity series $($such as sodium, magnesium, calcium, aluminium, etc.$),$ is very reactive and cannot be obtained from its compound by heating with carbon.
Therefore, such metals are obtained by electrolytic reduction of their molten salt.
For example, sodium is obtained by the electrolysis of molten sodium chloride $\ce{(NaCl)}$.

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