The s-Block Elements Test 9

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The s-Block Elements Test 9

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following imparts violet colouration to the Bunsen burner non-luminous flame?

A
$$NaCl$$

B
$${BaCl_2}$$

C
$${CaCl_2}$$

D
$$KCl$$

Solution

Violet colouration to the Bunsen burner will be produced by potasium, so $$KCl$$ imparts violet colouration to the Bunsen burner non-luminous flame.
Hence option D is correct.
Question 2
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Which of the following does not give an oxide on heating?

A
$$MgC{O}_{3}$$

B
$${Li}_{2}C{O}_{3}$$

C
$$ZnC{O}_{3}$$

D
None of the above

Solution

On thermal decomposition:
$$MgC{O}_{3}\rightarrow MgO+CO_2$$
$${Li}_{2}C{O}_{3}\rightarrow Li_2O+CO_2$$
$$ZnC{O}_{3}\rightarrow ZnO+CO_2$$
All of the above compounds gives oxides.
Hence option D is correct.
Question 3
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If $$X$$ and $$Y$$ are the second ionisation potentials of alkali and alkaline earth metals of same period, then :

A
$$X > Y$$

B
$$X < Y$$

C
$$X = Y$$

D
$$X << Y$$

Solution

The general electronic configuration of Alkali metal is $$ns^{1}$$ so if we remove first electron(first ionization energy) it will become octet configuration,so to remove next electron it requires more energy(second ionization energy) ,whereas the general electronic configuration of alkali earth metals is $$ns^{2}$$ so the electrons can be lost easily.,so the second ionization energy of alkali metal is more than the alkali earth metal,so the order of ionization energy is $$X > Y$$.
Hence option A is correct.
Question 4
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Which of the following hydride is covalent and polymeric?

A
$${CaH_2}$$

B
$${BeH_2}$$

C
NaH

D
$${BaH_2}$$

Solution

Due to small size and high Ionization energy, $$Be$$ always form covalent bonds, but $$BeH_2$$ is an unstable molecule due to incomplete octet so it forms polymer ($$BeH_2$$)n
Each beryllium atom is bonded to two hydrogen atoms and each hydrogen atom to two beryllium atoms. Now, beryllium has only two valence electrons and hydrogen only one, it is apparent that there are not sufficient electrons to form so many electron-pair bonds.
The monomeric $$BeH_2$$, if formed with normal bonds, would have only four electrons in the valence shell of the beryllium atom and would be electron-deficient and unstable. It polymerizes to remedy the electron deficiency.
The bonds formed cannot be explained by the classical theories of bonding. They are banana-shaped molecular orbitals holding three atoms $$Be ---- H ---- Be$$ together and are called $$3$$ centred $$2-$$ electron ($$3c 2e$$) bonds. It is an example of a cluster compound.
Hence option B is correct.
Question 5
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Which of the following does not illustrate the anomalous properties of $$Li$$?

A
The m.p. and b.p. of $$Li$$ are comparatively high

B
$$Li$$ is much softer than the other I group metals

C
$$Li$$ forms a nitride $${Li_3N}$$ unlike group I metals

D
The ion of $$Li$$ and its compounds are more heavily hydrated than those of the rest of the group

Solution

Anomalous behavior of lithium is due to extremely small size of lithium. Its cation on account of small size and high nuclear charge, lithium exerts the greatest polarizing effect out of all alkali metals on negative ion. Consequently, lithium ion possesses remarkable tendency towards solvation and develops covalent character in its compounds. $$Li$$ differs from other alkali metals in the following respects:

(1) It is comparatively harder than other alkali metals. $$Li$$ cannot be stored in kerosene as it floats to the surface, due to its very low density. $$Li$$ is generally kept wrapped in paraffin wax.
(2) It can be melted in the dry air without losing its brilliance.
(3) Unlike other alkali metals, lithium is least reactive among all. It can be noticed by the following properties,
(i) It is not affected by air.
(ii) It decomposes water very slowly to liberate $$H_2$$.
(iii) It hardly reacts with bromine while other alkali metals react violently.
(4) Lithium is the only alkali metal which directly reacts with $$N_2$$ to form lithium nitride ($$Li_3N$$)
(5) Lithium when heated in $$NH_3$$ forms amide, $$Li_2NH$$ while other metals form amides, $$MNH_2$$.
(6) When burnt in air, lithium form $$Li_2O$$ sodium form $$Na_2O$$ and $$Na_2O_2$$ other alkali metals form monoxide, peroxide and superoxide.
(7) $$Li_2O$$ is less basic and less soluble in water than other alkali metals.
(8) $$LiOH$$ is a weaker base than $$NaOH$$ or $$KOH$$ and decomposes on heating.
(9) The ion of $$Li$$ and its compounds are more heavily hydrated than those of the rest of the group
Hence, option $$B$$ is correct.
Question 6
1 / -0

Bone ash contains :

A
$$CaF_2$$

B
$${CaSO_4}$$

C
$${Ca_3(PO_4)_2}$$

D
$${Ca(H_2PO_4)_2}$$

Solution

The approximate formula of bone ash is $$ 4Ca_3(PO_4)_2.CaO$$ .Although raw bone is chemically $$Ca_3(OH)(PO_4)_3$$ hydroxyapatite.
Hence option C is correct.
Question 7
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The different products of Na and Li in dry air are :

A
$$ NaOH, Na_2O, Li_2O $$

B
$$ Na_2O, Na_3N, Li_2O, Li_3N $$

C
$$ Na_2O, Li_2O, Li_3, NH_3 $$

D
$$ Na_2O, Li_3N, Li_2O $$

Solution

Li reacts with $$ N_2 $$ and $$ O_2 $$ of air forming $$ Li_3N $$ and $$ Li_2O $$ but Na reacts with only $$ O_2 $$ forming $$ Na_2O $$. It does not react with $$ N_2 $$ forming $$ Na_3N $$ (it requires high temperature).
Question 8
1 / -0

Considering their electron affinities, do you think the alkali metals can form an anion like $$\mathrm{M^-}$$, where M represents an alkali metal?

A
Yes, due to stable $$ns^1$$ configuration.

B
No, due to stable $$ns^1$$ configuration.

C
Yes, due to stable $$ns^2$$ configuration.

D
No, due to unstable $$ns^2$$ configuration.
Question 9
1 / -0

In certain matters, lithium differs from other alkali metals, the main reason for this is:

A
Small size of lithium atom and $$Li^+$$ ion

B
Extremely high electro positivity of $$Li$$

C
Greater hardness of $$Li$$

D
Hydration of $$Li^+$$ ion
Question 10
1 / -0

The increasing order of solubility is :

A
$${CaCO_3}$$,$${KHCO_3}$$,$${NaHCO_3}$$

B
$${NaHCO_3}$$,$${KHCO_3}$$,$${CaCO_3}$$

C
$${KHCO_3}$$,$${NaHCO_3}$$,$${CaCO_3}$$

D
$${CaCO_3}$$,$${NaHCO_3}$$,$${KHCO_3}$$

Solution

Hint: Solubility means the tendency of a species to dissolve in any solvent.
Explanation:

$$NaHCO_3$$ and $$KHCO_3$$ dissociates as-

$$NaHCO_3\rightarrow Na^++HCO_3^-$$

$$KHCO_3\rightarrow K^++HCO_3^-$$

Both of them give same annion but the size of sodium ion is less than that of potassium. So, $$NaHCO_3$$ have low lattice energy than $$KHCO_3$$ and its tendency to dissolve in water is also low.

$$CaCO_3$$ dissociates as-

$$CaCO_3\rightarrow Ca^{+2}+CO_3^{2-}$$.

$$Ca^{+2}$$ have high charge density than $$K^+,Na^+$$ so, it have low lattice energy than sodium bicarbonate and potassium bicarbonate and also have the lowest solubility.

The increasing order of solubility is-

$$CaCO_3<NaHCO_3<KHCO_3$$.

Fianl Answer: The increasing order of solubility is-

$$CaCO_3,NaHCO_3,KHCO_3$$.

Correct option (D).

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Re-Attempt Weekly Quiz Competition

The s-Block Elements Test 9

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The s-Block Elements Test 9

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Question 1

$$NaCl$$

$${BaCl_2}$$

$${CaCl_2}$$

$$KCl$$

Solution

Question 2

$$MgC{O}_{3}$$

$${Li}_{2}C{O}_{3}$$

$$ZnC{O}_{3}$$

None of the above

Solution

Question 3

$$X > Y$$

$$X < Y$$

$$X = Y$$

$$X << Y$$

Solution

Question 4

$${CaH_2}$$

$${BeH_2}$$

NaH

$${BaH_2}$$

Solution

Question 5

The m.p. and b.p. of $$Li$$ are comparatively high

$$Li$$ is much softer than the other I group metals

$$Li$$ forms a nitride $${Li_3N}$$ unlike group I metals

The ion of $$Li$$ and its compounds are more heavily hydrated than those of the rest of the group

Solution

Question 6

$$CaF_2$$

$${CaSO_4}$$

$${Ca_3(PO_4)_2}$$

$${Ca(H_2PO_4)_2}$$

Solution

Question 7

$$ NaOH, Na_2O, Li_2O $$

$$ Na_2O, Na_3N, Li_2O, Li_3N $$

$$ Na_2O, Li_2O, Li_3, NH_3 $$

$$ Na_2O, Li_3N, Li_2O $$

Solution

Question 8

Yes, due to stable $$ns^1$$ configuration.

No, due to stable $$ns^1$$ configuration.

Yes, due to stable $$ns^2$$ configuration.

No, due to unstable $$ns^2$$ configuration.

Question 9

Small size of lithium atom and $$Li^+$$ ion

Extremely high electro positivity of $$Li$$

Greater hardness of $$Li$$

Hydration of $$Li^+$$ ion

Question 10

$${CaCO_3}$$,$${KHCO_3}$$,$${NaHCO_3}$$

$${NaHCO_3}$$,$${KHCO_3}$$,$${CaCO_3}$$

$${KHCO_3}$$,$${NaHCO_3}$$,$${CaCO_3}$$

$${CaCO_3}$$,$${NaHCO_3}$$,$${KHCO_3}$$

Solution

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