Question

A.What is the valency of Nitrogen in the following compounds?
i) $N_2{O}_3$ ii) $N_2{O}_5$ iii) $N{O}_2$ [3 marks]

B. (i) Why metallic character decreases across a period and increases down a group? [1 mark]

(ii) Considering the atomic number and position in the periodic table, arrange the following elements in the increasing order of metallic character: $Si,Be,Mg,Na,P.$ [2 marks]

C. (i) Explain why:
(a) Fused $CaC{l}_2$ or concentrated $H_{2}S{O}_4$ is used in desiccator. [1 mark]
(b) Effervescence is seen on opening a bottle of soda water.
[1 mark]

(ii) Explain the permutit process for softening hard water. [2 marks]

Answer 1

A. (i) In $N_2{O}_5$, there are two nitrogen atoms and five oxygen atoms. As a result, it has a valency of 5. [1 mark]
(ii) In $N_2{O}_3$, there are two nitrogen atoms and three oxygen atoms. As a result, it has a valency of 3. [1 mark]
(iii) In $N{O}_2$, the charge of oxygen is -2 and the charge on the nitrogen is: x + 2(-2) = 0 x = +4 [1 mark]

B. (i) As the effective nuclear charge acting on the valence shell electrons increases across a period, the tendency to lose electrons will decrease.
Down the group, the effective nuclear charge experienced by valence electrons decreases because the outermost electrons move farther away from the nucleus. Therefore, these can be lost easily. [1 Mark]
Hence metallic character decreases across a period and increases down a group.

(ii) Arranging the elements into different groups and periods in order of their increasing atomic numbers.

$1$ $2$ $13$ $14$ $15$

----- $Be$ ---- ----- -----

$Na$ $Mg$ ---- $Si$ $P$

We know, metallic character increases down a group and decreases along a period as we move from left to right. [1 Marks]

Therefore, $Na$ is the most metallic element, followed by $Mg$ and $Si$ while $P$ is the least metallic element. Comparing $Be$ and $Mg,Mg$ is more metallic than $Be.$ [1 mark]

So, the overall order of increasing metallic character is:
$P<Si<Be<Mg<Na$ [1 mark]

C. (i)
(a) Fused $CaC{l}_2$ or concentrated $H_{2}S{O}_4$ are deliquescent by nature and they absorb moisture. Hence, they are used as desiccator. [1 mark]

(b) The solubility of carbon dioxide in water is increased when water is subjected to higher pressure. Thus on opening a soda water bottle, the dossolved gas immediately bubbles out or show efferevescence since pressure on the surface of water suddenly decreases. [1 mark]

(ii) Permutit is an artificial zeolite. Chemically, it is hydrated sodium aluminium orthosilicate with the formula $N{a}_{2}A{l}_{2}S{i}_2{O}_8.x{H}_{2}O$. [1 Marks]

A tall cylinder is loosely filled with lumps of permutit. Ions gets exchanged when hard water containing calcium and magnesium ions percolates through these lumps. Sodium permutit is slowly changed into calcium and magnesium permutit, and the water becomes soft with the removal of calcium and magnesium ions.
[1 mark]