The s-Block Elements Test 39

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The s-Block Elements Test 39

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Question 1
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Directions For Questions

$$P,Q$$ and $$R$$ are three elements with atomic numbers, $$Z-1,Z$$ and $$Z+1$$ respectively. $$Q$$ is an inert gas.

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Identify the elements having same valence shell.

A
$$P$$ and $$Q$$

B
$$Q$$ and $$R$$

C
$$P$$ and $$R$$

D
$$P$$, $$Q$$ and $$R$$
Question 2
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Why is $$LiF$$ almost insoluble in water whereas $$LiCl$$ is soluble not only in water but also in acetone?

A
For a substance to dissolve in water, its hydration energy must be greater than its lattice energy.

B
Due to small size of $$Li^+$$ ion and $$F^-$$ ions, lattice energy of $$LiF$$ is very high. $$LiF$$ is covalent in nature. Therefore, $$LiF$$ is insoluble in water.

C
Due to larger size of $$Cl^-$$ ion, the lattice energy of $$LiCl$$ is less than its hydration energy. Hence, $$LiCl$$ is soluble in water and in acetone.

D
Due to the large size of $$F^-$$ ion and high hydration energy, the $$LiF$$ is insoluble in water.

Solution

$$\rightarrow$$ Lattice energy is defined as the amount of energy required to separate one mole of ionic compound into its gaseous ions.
$$\rightarrow$$ Lattice energy of $$LiF\rightarrow$$ $$1009$$ KJ/mol
$$LiCl\rightarrow$$ $$845$$ KJ/mol
$$\rightarrow$$ HIgher the lattice point, higher is the melting point of the alkali metal which halide and hence lower is its solubility in water.
$$\rightarrow$$ Hence, $$LiF$$ is almost insoluble in water, while $$LiCl$$ is soluble in water and acetone.
Question 3
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Choose the correct answer form the alternatives given.
When alkaline earth metals dissolve in ammonia, they form coloured solution like alkali metals . Which of the following observations regarding the reaction are correct?
(i) Dilute solution are bright blue in colour due to solvated electrons.
(ii) These solutions decompose to form amides and hydrogen.
(iii) From this solution the ammoniates $$[M(NH_3)_6]^{2+}$$ can be recovered by evaporation.

A
Only (i) and (ii)

B
Only (i) and (ii) and (iii)

C
Only (ii) and (iii)

D
Only (i)
Solution
All alkali metal dissolve in liquid ammonia giving deep blue solutions which are conducting in nature. These solutions contain ammoniated cations and ammoniated electrons as shown below:
$$M + ( x + y ) NH_3 \rightarrow M+(NH_3 )_x + e^-(NH_3)_y$$
The blue colour of the solution is considered to be due to ammoniated electrons which absorb energy corresponding to red region of the visible light for the their excitation to higher energy levels. The transmitted light is blue which imparts blue colour to the solutions.
From this solution the ammoniates $$[M(NH_3)_6]^{2+}$$ can be recovered by evaporation.
These solutions decompose to form amides and hydrogen.
Question 4
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Beryllium shows a diagonal relationship with aluminium. Which of the following similarity is incorrect?

A
$$Be_2C$$ like $$Al_4C_3$$ yields methane on hydrolysis .

B
Be like Al is rendered passive by $$HNO_3$$.

C
$$Be(OH)_2$$ like $$Al(OH)_3$$ is basic.

D
Be forms beryllates A1 forms aluminates.

Solution

The two structures involve the only movement of electrons and not of atoms or groups, hence these are resonating structures. Both metals have the tendency to form covalent compounds Diagonal relationship of Be with Al Because of its small size. Be differs from other earth alkaline earth metals but resembles in many of its properties with Al on account of the diagonal relationship.

The correct option is that $$Be (OH)_{2} $$ like $$Al (OH)_{3}$$ both are basic in nature.
The correct answer is C.
Question 5
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Choose the correct answer form the alternatives given.
Which of the following compounds are not arranged in correct order as indicated?

A
$$SrCl_2 < CaCl_2 < MgCl_2 < BeCl_2$$(increasing extent of hydrolysis)

B
$$SrCl_2 < CaCl_2 < MgCl_2 < BeCl_2$$(increasing lattice energy)

C
$$CaSO_4 < MgSO_4 < BeSO_4 $$(increasing stability)

D
$$Be(OH)_2 < Mg(OH)_2 < Ca(OH)_2$$(increasing solubility)

Solution

$$BeSO_4 < MgSO_4 < CaSO_4$$(increasing stability)
Temp.of Decomposition of $$BeSO_4 , MgSO_4 , CaSO_4$$ are 773K ,11681 K and 1422K respectively.
Question 6
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What is the biological importance of $$Na^+$$ and $$K^+$$ ions in cell fluids like blood plasma?

A
They participate in transmission of nerve signals .

B
They regulate the number of red and white blood corpuscles in the cell.

C
They can be present in any amount in the blood since they are absorbed by the cells.

D
They regulate the viscosity and colour of the blood.

Solution

The process of moving sodium and potassium ions across the cell membrane is an active transport process involving the hydrolysis of ATP to provide the necessary energy. It involves an enzyme refer to as $$ { Na }^{ + }/{ K }^{ + }-ATPase $$. This process is responsible for maintaining the large excess of $$ { Na }^{ + } $$ outside the cell and the large excess of $$ { K }^{ + } $$ ions on the inside.
It accomplishes the transport of three $$ { Na }^{ + } $$ to the outside of the cell and the transport of two $$ { K }^{ + } $$ ions to the inside. This unbalanced charge transfer contributes to the separation of charge across the membrane. The sodium-potassium pump is an importance contributor to action potential produced by nerve cells.
The $$ { Na }^{ + } $$ and $$ { K }^{ + } $$ ions participate in the transmission of nerve signals.
Question 7
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A metal M reacts with nitrogen to give nitride which on reaction with water produces ammonia gas. Metal M can be:

A
Na

B
K

C
Li

D
Rb

Solution

The metal Lithium shows an exceptional behaviour by reacting in atmosphere of nitrogen to give lithium nitride $${Li}_{3}N$$ which upon reaction with water produces ammonia gas.
$$6Li+ {N}_{2}\rightarrow3{Li}_{3}N$$
$$3Li_{3}N+H_{2}\rightarrow 3LiOH + NH_{3}$$
Question 8
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Which among the following elements of group-$$2$$ exhibit anomalous properties?

A
Be

B
Mg

C
Ca

D
Ba

Solution

Be exhibit anomalous properties. This is due to smaller atomic and ionic radii of beryllium as compared to other group members. It is also due to the higher electronegativity of Be.
Question 9
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Sulphates of Be and Mg are readily soluble in water but sulphates of Ca, Sr and Ba are insoluble. This is due to the fact that:

A
the greater hydration enthalpies of $$Be^{2+} and Mg^{2+}$$ overcome the lattice enthalpy

B
high lattice enthalpy of $$Be^{2+}$$ and $$Mg^{2+}$$ makes them soluble in water

C
solubility decreases from $$BeSO_4$$ to $$BaSO_4$$ due to increase in ionic size

D
$$BeSO_4$$ and $$MgSO_4$$ are ionic in nature while other sulphates are covalent

Solution

Due to smaller size their lattice enthalpies are high but their greater hydration enthalpies overcome the lattice enthalpies and they become soluble in water. Ca,Sr and Ba sulphates are insoluble is water due to lower hydration enthalpies.
Question 10
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Beryllium and aluminium exhibit many properties which are similar. But, the two elements differ in:

A
Forming covalent halides

B
Forming polymeric hybrids

C
Exhibiting maximum covalency in compounds

D
Exhibiting amphoteric nature in their oxides

Solution

Due to diagonal relationship, Be and Al exhibits similar properties But covalency of $$Be$$ is 4 because it has an absence of d-orbital whereas, covalency of $$Al$$ is up to 6 due to the presence of vacant d-orbital.
Hence they differ in (C) Exhibiting the maximum covalency in compounds.

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The s-Block Elements Test 39

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Question 1

$$P$$ and $$Q$$

$$Q$$ and $$R$$

$$P$$ and $$R$$

$$P$$, $$Q$$ and $$R$$

Question 2

For a substance to dissolve in water, its hydration energy must be greater than its lattice energy.

Due to small size of $$Li^+$$ ion and $$F^-$$ ions, lattice energy of $$LiF$$ is very high. $$LiF$$ is covalent in nature. Therefore, $$LiF$$ is insoluble in water.

Due to larger size of $$Cl^-$$ ion, the lattice energy of $$LiCl$$ is less than its hydration energy. Hence, $$LiCl$$ is soluble in water and in acetone.

Due to the large size of $$F^-$$ ion and high hydration energy, the $$LiF$$ is insoluble in water.

Solution

Question 3

Only (i) and (ii)

Only (i) and (ii) and (iii)

Only (ii) and (iii)

Only (i)

Solution

Question 4

$$Be_2C$$ like $$Al_4C_3$$ yields methane on hydrolysis .

Be like Al is rendered passive by $$HNO_3$$.

$$Be(OH)_2$$ like $$Al(OH)_3$$ is basic.

Be forms beryllates A1 forms aluminates.

Solution

Question 5

$$SrCl_2 < CaCl_2 < MgCl_2 < BeCl_2$$(increasing extent of hydrolysis)

$$SrCl_2 < CaCl_2 < MgCl_2 < BeCl_2$$(increasing lattice energy)

$$CaSO_4 < MgSO_4 < BeSO_4 $$(increasing stability)

$$Be(OH)_2 < Mg(OH)_2 < Ca(OH)_2$$(increasing solubility)

Solution

Question 6

They participate in transmission of nerve signals .

They regulate the number of red and white blood corpuscles in the cell.

They can be present in any amount in the blood since they are absorbed by the cells.

They regulate the viscosity and colour of the blood.

Solution

Question 7

Na

K

Li

Rb

Solution

Question 8

Be

Mg

Ca

Ba

Solution

Question 9

the greater hydration enthalpies of $$Be^{2+} and Mg^{2+}$$ overcome the lattice enthalpy

high lattice enthalpy of $$Be^{2+}$$ and $$Mg^{2+}$$ makes them soluble in water

solubility decreases from $$BeSO_4$$ to $$BaSO_4$$ due to increase in ionic size

$$BeSO_4$$ and $$MgSO_4$$ are ionic in nature while other sulphates are covalent

Solution

Question 10

Forming covalent halides

Forming polymeric hybrids

Exhibiting maximum covalency in compounds

Exhibiting amphoteric nature in their oxides

Solution

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