Tag: the s-block elements (alkali and alkaline earth metals)

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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

Choose the correct answer form the alternatives given.
Which of the following has lowest thermal stability?

  1. $Li _2CO _3$
  2. $Na _2CO _3$
  3. $K _2CO _3$
  4. $Rb _2CO _3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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 } $

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

Fill up the blanks with appropriate choices.
Lithium and magnesium react slowly with water. Their hydroxides are ________ soluble in water. Carbonates are Li and Mg ________ easily on heating. Both LiCl and $MgCl 2$ are _______ in entanol and are _____. They crystallise from their aqueous solutions as ______.

  1. more, do not decompose, soluble, hygroscopic, hydrates

  2. less, decompose, soluble, deliquescent, hydrates

  3. freely, sublime, insoluble, deliquescent, anhydrous

  4. freely, decompose, soluble, hygroscopic, crystals
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A Diagonal Relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table. These pairs (Li & Mg, Be & Al, B & Si etc.) exhibit similar properties.

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 is used as a sources of hydrogen for filling of balloons that is convenient and can be carried around?

  1. Lithium hydride

  2. Sodium borohydride

  3. Calcium metal

  4. Sodium formate
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • LiH is produced by treating lithium metal with hydrogen gas.
  • It is used for filling meteorological balloons which carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde
Hence option A 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

The solubility of metal halides depends on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluorides of alkali metals, the lowest solubility of LiF in water is due to:

  1. ionic nature of lithium fluoride

  2. high lattice enthalpy

  3. high hydration enthalpy for lithium ion

  4. low ionisation enthalpy of lithium atom
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lowest solubility of $LiF$ is due to high lattice enthalpy which is higher than hydration enthalpy. Hence, the dissociation of $Li-F$ bond becomes difficult.

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

$Li$ has an abnormal behaviour in its group, which is ____________.

  1. lithium carbonate decomposes into its oxide on heating unlike other elements.
  2. $LiCl$ is covalent in nature.
  3. $Li _3N$ is a stable compound.
  4. $LiCl$ is a good conductor of electricity in the molten state.
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

(A). Lithium carbonate, being less stable, decomposes into its oxide on heating, whereas other group IA carbonates are stable and do not decompose.


${ Li } _{ 2 }C{ O } _{ 3 }\ \underrightarrow { \triangle  } \ { Li } _{ 2 }O+C{ O } _{ 2 }$

(B). Lithium halides, except fluoride, are covalent due to fajan's rule.

(C) Lithium is the only 1A metal that can combine with inert nitrogen in air to form lithium nitride.

(D) Lithium chloride , like other alkali metals compounds , is a good conductor of electricity in molten state. 

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

Alkali metals readily react with oxyacids forming corresponding salts like ${ M } _{ 2 }{ CO } _{ 3 }$, ${ M }H{ CO } _{ 3 }$, ${ M }N{ O } _{ 3 }$, ${ M } _{ 2 }{ SO } _{ 4 }$, etc. with evolution of hydrogen. They also dissolve in liquid ${ NH } _{ 3 }$ but without the evolution of hydrogen. The color of its dilute solution is blue but when it is heated and concentrated then its color becomes bronze.

Which of the following statement about the sulphate of alkali metal is correct :

  1. except ${ Li } _{ 2 }{ SO } _{ 4 }$ all sulphate of other alkali metals are soluble in water.

  2. all sulphates of alkali metals except lithium sulphate forms alum.

  3. the sulphates of alkali metals cannot be hydrolysed.

  4. all of these.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Except ${ Li } _{ 2 }{ SO } _{ 4 }$ all sulphate of other alkali metals are soluble in water and forms alum. Thus, they form double salts with the sulphates of trivalent metals like $Al, Fe, Cr$ etc. The sulphates of alkali metals cannot be hydrolysed as they are salts of a strong acid and strong base. 
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 statement(s) is/are true?

  1. Both $LiCl$ and $MgCl _{2}$ are deliquescent.

  2. Lithium is least reactive but the strongest reducing agent amongst all the alkali metals.

  3. Liquid sodium metal is used as a coolant in fast breeder nuclear reactors.

  4. Lithium iodide is the most ionic in nature among all alkali metal halides.
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

(A) $Li^{+}$ and $Mg^{2+}$ have higher polarising power and thus attract more number of water molecules.
(B) $Li$ is least reactive because of its highest ionisation energy on account of smaller size.
(C) It is one of the uses of liquid sodium as it has low melting point.
(D) $LiI$ is the most covalent due to smaller cation and bigger anion (according to Fajan's rule).

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

$LiOH$ reacts with $CO {2}$ to form $Li _{2}CO _{3}$ (atomic mass of $Li = 7)$. The amount of $CO _{2}$ (in g) consumed by $1\ g$ of $LiOH$ is closest to ______.

  1. $0.916$
  2. $1.832$
  3. $0.544$
  4. $1.088$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Balanced chemical equation is:

$2LiOH+C{ O } _{ 2 }\rightarrow { Li } _{ 2 }C{ O } _{ 3 }+{ H } _{ 2 }O$
Molecular weight of each specie is:
$LiOH$=24 g/mol; $C{ O } _{ 2 }$=44 g/mol; ${ Li } _{ 2 }C{ O } _{ 3 }$= 74 g/mol; ${ H } _{ 2 }O$=18 g/mol
From the reaction:
2 mol of $LiOH$ ($24\times2=48\ g$) consumes 1 mol of $CO _2$ (44 g)
Therefore, 1 g of $LiOH$ will consume $\frac { 1 }{ 48 } \times 44\quad g\quad C{ O } _{ 2 }=0.916\ g\ CO _2$
Option A is the 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

Diagonal relationship of elements in due to same:

  1. size

  2. mass number

  3. atomic number

  4. electron affinity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
In addition to horizontal and vertical trends, there is a diagonal relationship between elements such as Li and Mg, Be and Al, B, and Si, that have an adjacent upper left/lower right relative location in the periodic table. 
These pairs of elements have similar size and electronegativity, resulting in similar properties. 

Diagonal relationships occur because of the directions in the trends of various properties as you move across or down the periodic table. Many of the chemical properties of an element are related to the size of the atom. Hence it is because of the same size.
Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

The reaction of water with slaked lime is studied by ________ .

  1. putting slaked lime into water taken in a test tube

  2. putting a lot of water into slaked lime.

  3. sprinkling a little water on slaked lime.

  4. none of the above method.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The reaction of water with calcium oxide (quicklime) to form slaked lime is highly exothermic. To study it safely, one typically adds small amounts of water to the lime or vice-versa under controlled conditions, but the standard laboratory demonstration involves adding water to the solid.