The s-Block Elements Test 19

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The s-Block Elements Test 19

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Question 1
1 / -0

Among the following the least thermally stable is:

A
$$K_{2}CO_{3}$$

B
$$Na_{2}CO_{3}$$

C
$$BaCO_{3}$$

D
$$Li_{2}CO_{3}$$

Solution

Thermal stability of carbonates increases on moving down a group. Thus, lithium carbonate, $$Li_{2}CO_{3}$$ is least thermally stable.
$$Li_{2}CO_{3}\xrightarrow {\triangle} Li_{2}O + CO_{2}\uparrow$$.
Question 2
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The set representing the correct order of ionic radii is:

A
$${ Li }^{ + }>{ Be }^{ 2+ }>{ Na }^{ + }>{ Mg }^{ 2+ }$$

B
$${ Na }^{ + }>{ Li }^{ + }>{ Mg }^{ 2+ }>{ Be }^{ 2+ }$$

C
$${ Li }^{ 2+ }>{ Na }^{ + }>{ Mg }^{ 2+ }>{ Be }^{ 2+ }$$

D
$${ Mg }^{ 2+ }>{ Be }^{ 2+ }>{ Li }^{ + }>{ Na }^{ + }$$

Solution

The ionic radius in general increases on moving from top to bottom in a group and decreases on moving from left to right in a period.
Hence, correct order is
$$\underset { 0.95\mathring { A } }{ { Na }^{ + } } >\underset { 0.68\mathring { A } }{ { Li }^{ + } } >\underset { 0.65\mathring { A } }{ { Mg }^{ 2+ } } >\underset { 0.63\mathring { A } }{ { Be }^{ 2+ } } $$
Question 3
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Which of the following is a false statement?

A
Sodium oxide is more basic then magnesium oxide

B
Beryllium oxide is amphoteric.

C
The thermal stability of beryllium carbonate is more than that of calcium carbonate

D
Lithium chloride is deliquescent.

Solution

As we go down the group in the periodic table the thermal stability of the carbonates increases, because down the group, polarisation decreases, due to increase in size of metal. So, thermal stability of $${ BeCO }_{ 3 }$$ is less than that of $${ CaCO }_{ 3 }$$.
Question 4
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Which alkaline earth metal compound is volatile?

A
$$Mg_{3}N_{2}$$

B
$$Ca_{3}N_{2}$$

C
$$Be_{3}N_{2}$$

D
None of the option

Solution

$$Be_{3}N_{2}$$ is volatile due to greater tendency of covalent character in $$Be$$ and $$N$$ atoms. All other nitrides are of ionic nature.
Question 5
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Which of the following substances are formed when lithium is heated in air?

A
$${ Li }_{ 2 }O+Li{ O }_{ 2 }$$

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

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

D
$$Li_2{ O }_{ }+{ Li }_{ 3 }N\quad $$

Solution

$$2Li+\cfrac { 1 }{ 2 } { O }_{ 2 }\longrightarrow { Li }_{ 2 }O$$

$$6Li+{ N }_{ 2 }\longrightarrow 2{ Li }_{ 3 }N$$

A mixture of $${ Li }_{ 2 }O$$ and $${ Li }_{ 3 }N$$
Question 6
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Choose the correct answer form the alternatives given.
Which of the following has lowest thermal stability?

A
$$Li_2CO_3$$

B
$$Na_2CO_3$$

C
$$K_2CO_3$$

D
$$Rb_2CO_3$$

Solution

Lithium carbonates are least thermal stable compound which decompose upon heating to give lithium oxide and carbon dioxide.
$$ { Li }_{ 2 }C{ O }_{ 3 }\ \rightarrow { Li }_{ 2 }O\ +\ C{ O }_{ 2 } $$
Question 7
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Choose the correct answer form the alternatives given.
Which of the following statements is not true about alkali metals ?

A
All alkali metals from oxo salts such as carbonates, sulphates and nitrates.

B
The basic character of oxides increases down the group.

C
Carbonates and sulphates of lithium are stable and their stability decreases down the group.

D
Solubility of carbonates and sulphates increases down the group.
Solution
Characteristics of Alkali Metals-
Found in column 1A of the periodic table.
Have one electron in their outermost layer of electrons.
Easily ionized.
Silvery, soft, and not dense.
Low melting points.
Incredibly reactive.
They form oxo salts such as carbonates, sulphates and nitrates.
The basic character of oxides increases down the group.
The acidic character of oxides decreases down the group.
Solubility of carbonates and sulphates increases down the group.
As we move down the alkali metal group, the electropositive character increases. This causes an increase in the stability of alkali carbonates. However, lithium carbonate is not so stable to heat. This is because lithium carbonate is covalent.
Hence option C is not correct about alkali metals.
Question 8
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Choose the correct answer form the alternatives given.
A solution of a compound $$X$$ in dilute $$HCl$$ on treatment with a solution of $$BaCl_2$$ gives a white precipitate of compound $$Y$$ which is insoluble in conc. $$HNO_3$$ and conc. $$HCl$$. Compound $$X$$ imparts golden yellow colour to the flame.
$$\underset{(\text{imparts golden yellow colour})}{X (\text{solution in dilute HCl})}+BaCl_2\longrightarrow \underset{white \\ ppt}{Y} \xrightarrow[Conc Hcl]{Conc.HNO_3\\ +} Insoluble$$
What are compounds $$X$$ and $$Y$$?

A
$$X$$ is $$MgCl_2$$ and $$Y$$ is $$BaSO_4$$

B
$$X$$ is $$CaCl_2$$ and $$Y$$ is $$BaSO_4$$

C
$$X$$ is $$Na_2SO_4$$ and $$Y$$ is $$BaSO_4$$

D
$$X$$ is $$MgSO_4$$ and $$Y$$ is $$BaSO_4$$

Solution

$$\underset{(\text{imparts golden yellow colour})}{X (\text{solution in dilute HCl})}+BaCl_2\longrightarrow \underset{white \\ ppt}{Y} \xrightarrow[Conc Hcl]{Conc.HNO_3\\ +} Insoluble$$
Thecompounds $$X$$ and $$Y$$ are
$$Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl $$
(X) (Y)
Question 9
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The properties of $$Li$$ are similar to those of $$Mg$$. This is because:

A
both have nearly the same size.

B
both has their charge to size ratio nearly the same.

C
both have similar electronic configurations.

D
both are found together in nature.
Solution
- The properties of lithium are similar to those of $$Mg$$ because they are having diagonal relationship.
- The elements having diagonal relationship show similar properties and the reason is because the both of them will have similar electronegativity and polarising power i.e. charge per size ratio of both the elements are nearly the same.
Question 10
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For a given sample of water containing the following impurities
$$Mg{ \left( H{ CO }_{ 3 } \right) }_{ 2 }=73mg/L;\quad Ca{ \left( H{ CO }_{ 3 } \right) }_{ 2 }=162mg/L;\quad Ca{ SO }_{ 4 }=136mg/L$$
$$Mg{ Cl }_{ 2 }=95mg/L;\quad Ca{ Cl }_{ 2 }=111mg/L;\quad NaCl=100mg/L$$
Then the total hardness (temporary and permanent) of above water sample is?

A
$$300ppm$$

B
$$350ppm$$

C
$$450ppm$$

D
$$500ppm$$

Solution

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The s-Block Elements Test 19

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Question 1

$$K_{2}CO_{3}$$

$$Na_{2}CO_{3}$$

$$BaCO_{3}$$

$$Li_{2}CO_{3}$$

Solution

Question 2

$${ Li }^{ + }>{ Be }^{ 2+ }>{ Na }^{ + }>{ Mg }^{ 2+ }$$

$${ Na }^{ + }>{ Li }^{ + }>{ Mg }^{ 2+ }>{ Be }^{ 2+ }$$

$${ Li }^{ 2+ }>{ Na }^{ + }>{ Mg }^{ 2+ }>{ Be }^{ 2+ }$$

$${ Mg }^{ 2+ }>{ Be }^{ 2+ }>{ Li }^{ + }>{ Na }^{ + }$$

Solution

Question 3

Sodium oxide is more basic then magnesium oxide

Beryllium oxide is amphoteric.

The thermal stability of beryllium carbonate is more than that of calcium carbonate

Lithium chloride is deliquescent.

Solution

Question 4

$$Mg_{3}N_{2}$$

$$Ca_{3}N_{2}$$

$$Be_{3}N_{2}$$

None of the option

Solution

Question 5

$${ Li }_{ 2 }O+Li{ O }_{ 2 }$$

$${ Li }_{ 2 }{ O }_{ 2 }$$

$$Li{ O }_{ 2 }$$

$$Li_2{ O }_{ }+{ Li }_{ 3 }N\quad $$

Solution

Question 6

$$Li_2CO_3$$

$$Na_2CO_3$$

$$K_2CO_3$$

$$Rb_2CO_3$$

Solution

Question 7

All alkali metals from oxo salts such as carbonates, sulphates and nitrates.

The basic character of oxides increases down the group.

Carbonates and sulphates of lithium are stable and their stability decreases down the group.

Solubility of carbonates and sulphates increases down the group.

Solution

Question 8

$$X$$ is $$MgCl_2$$ and $$Y$$ is $$BaSO_4$$

$$X$$ is $$CaCl_2$$ and $$Y$$ is $$BaSO_4$$

$$X$$ is $$Na_2SO_4$$ and $$Y$$ is $$BaSO_4$$

$$X$$ is $$MgSO_4$$ and $$Y$$ is $$BaSO_4$$

Solution

Question 9

both have nearly the same size.

both has their charge to size ratio nearly the same.

both have similar electronic configurations.

both are found together in nature.

Solution

Question 10

$$300ppm$$

$$350ppm$$

$$450ppm$$

$$500ppm$$

Solution

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