Tag: properties of s block elements

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Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

The products obtained on heating $LiNO _3$ will be?

  1. $LiNO _2+O _2$
  2. $Li _2O+NO _2+O _2$
  3. $Li _3N+O _2$
  4. $Li _2O+NO+O _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When LiNO3 is heated, it decomposes to Li2O, NO2, and O2. This is typical thermal decomposition of lithium nitrate. Option A gives nitrite, option C suggests nitride formation, and option D gives NO instead of NO2.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which elements does not combine directly with nitrogen at high temperature?

  1. Li

  2. Rb

  3. Sr

  4. Mg
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Only $Rb$ does not combine with $N _2$ at high temperature. Because heavier metals like $Rb$ are seen to be chemically inactive towards $N _2$ upon heating.


Since the nitride ion holds a high formal charge $(N^{3-})$ and contains an adverse molar ration of cations to anions $(3:1)$ 

it is impossible to form a stable structure. But alkali metal $Li$ can react with $N _2$ at room temperature. $Sr$ and $Mg$ can react with $N _2$ at high temperature.

So, the correct option is $Rb$

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which of the following on heating gives oxides quickly ?

  1. ${ Na } _{ 2 }{ CO } _{ 3 }$
  2. ${ K } _{ 2 }{ CO } _{ 3 }$
  3. ${ Li } _{ 2 }{ CO } _{ 3 }$
  4. ${ Rb } _{ 2 }{ CO } _{ 3 }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$N{a _2}C{O _3} \to state\,\,than\,\,L{i _2}C{O _3}$

${K _2}C{O _3}$ and $R{b _2}C{O _3}$
Stablitiy of carbaonate $ \uparrow $ down the gap or size $ \uparrow    CO _3^{2 - } $ more stable.
$L{i _2}C{o _3} \to L{i _2}O + C{o _2}$.
Hence, option $C$ is correct answer.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which of the following illustrate the anomalous properties of Lithium?

  1. Lithium is softer than the other group I metals
  2. Lithium forms nitride, $Li _3N$ unlike other group I metals

  3. The melting and boiling point of Lithium are comparatively high

  4. none of these
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

Similarities of  lithium with magnesium and dissimilarities with that of the other members of the group

Lithium is a very strong element and is equally strong as magnesium.

Li forms $Li _3N$ with nitrogen.

It has high melting and boiling points. The boiling point of lithium is $1330$ degree centigrade that is comparable to that of magnesium which is $1100$ degrees.

Due to small size, the lithium atom has high ionization energy. Hence, it remains inactive to dry air, slowly reactivity with water, liquid bromine and forms a highly stable hydride unlike other alkali metals.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

$LiAlH 4$ is obtained by reacting an excess of ____  with an ethereal solution of $AlCl _3$:

  1. $LiCl$
  2. $LiH$
  3. $Li$
  4. $LiOH$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The reaction is ,


$4LiH + AlCl _3 \rightarrow LiAlH _4 + 3 LiCl$


by reacting $LiH$ in the presence of dry ether with $AlCl _3$ .

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

There is loss in weight when mixture of $Li _{2}CO _{3}$ and $Na _{2}CO _{3}\cdot10H _{2}O$ is heate strongly. This loss is due to :

  1. $Li _{2}CO _{3}$
  2. $Na _{2}CO _{3}\cdot10H _{2}O$

  3. both (a) and (b)

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Loss in weight due to following reactions:
$Li _{2}CO _{3} \rightarrow Li _{2}O+CO _{2} \uparrow$
$Na _{2}CO _{3}\cdot10H _{2}O \rightarrow Na _{2}CO _{3} + 10H _{2}O \uparrow$
As sodium carbonate is thermally stable so it will not dissociates on heating.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Nitrate can be converted into metal oxide on heating in case of :

  1. Li

  2. Na

  3. both (a) and (b)

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Reaction on heating:
$2LiNO _{3} \rightarrow Li _{2}O+2NO _{2}+ \frac{1}{2} O _{2}$
$Mg(NO _{3}) _{2} \rightarrow MgO+2NO _{2}+ \frac{1}{2} O _{2}$
$2NaNO _3\rightarrow 2NaNO _2+O _2$

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Lithium selenide can be described as a cubic closest-packed array of selenide ions with lithium ions in all of the tetrahedral holes. Formula of lithium selenide is 

  1. $L{i _2}Se$
  2. $LiSe$
  3. $LiS{e _2}$
  4. $L{i _3}Se$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer(A):- $Li _2Se$

If number of Se =Z , Number of Li = 2Z

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) anomalous properties of lithium group 1 elements: alkali metals properties of s block elements

Which one of the following species dose not exist under normal conditions?

  1. $Li _2$
  2. ${ Be } _{ 2 }^{ + }$
  3. $Be _2$
  4. $B _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Li2 (dilithium) does not exist under normal conditions due to poor orbital overlap and bond formation. Be2+ exists as the beryllium(II) ion, Be2 as a molecule is unstable but Be2+ is common. B2 exists as a diatomic molecule (paramagnetic with 2 unpaired electrons). The question asks which doesn't exist - Li2 is the correct answer.