Alkaline earth metals Questions in English

(C) The atomic number of calcium $(Ca)$ is $20$.
The electronic configuration of calcium is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$ or $(2, 8, 8, 2)$.
The valence shell is the outermost shell,which is the $4^{th}$ shell.
There are $2$ electrons in the $4s$ orbital of the valence shell.

(B) The solubility of alkaline earth metal fluorides decreases down the group due to the decrease in hydration energy being more significant than the decrease in lattice energy.
The solubility order is: $BeF_2 > MgF_2 > CaF_2 > SrF_2$.
Therefore,$SrF_2$ is the least soluble among the given options.

(B) The electronic configuration of element $X$ is $1s^2, 2s^2 2p^6, 3s^2$.
This indicates that the element has $2$ valence electrons in the $3s$ orbital.
Therefore,$X$ belongs to Group $2$ (alkaline earth metals) and typically forms a cation with a $+2$ charge $(X^{2+})$.
Since the chloride ion is $Cl^-$,the formula of the chloride formed is $XCl_2$.

(D) Ionic hydrides are typically formed by $s$-block elements (alkali and alkaline earth metals) with hydrogen.
$CaH_2$,$BaH_2$,and $SrH_2$ are all alkaline earth metal hydrides,which exhibit ionic character.
Therefore,all of the given options are correct.

(B) The correct option is $(B)$.
Due to its very small atomic size and high ionization enthalpy,$Be$ (Beryllium) has a high polarising power.
This leads to significant covalent character in its compounds,unlike the other alkaline earth metals $(Mg, Ca, Ba)$ which primarily form ionic compounds.

(B) $Beryllium$ $(Be)$ shows a diagonal relationship with $Aluminium$ $(Al)$.
This is because they have similar ionic potential (charge/size ratio) and electronegativity values.
Therefore,$Be$ resembles $Al$ in its chemical properties.

(A) The total number of electrons is $2+2+6+2 = 12$.
This corresponds to the element Magnesium $(Mg)$.
Since it has $2$ electrons in its outermost shell $(3s^2)$,it belongs to Group $2$ of the periodic table.
Elements in Group $2$ are known as alkaline earth metals.
Therefore,the element is a metal.

(D) The electronic configuration of $Be$ (Beryllium,atomic number $4$) is $1s^2 2s^2$.
It has $2$ electrons in its outermost shell $(n=2)$.
Therefore,the correct option is $(D)$.

(A) The hydration energy of an ion is directly proportional to its charge density,which is defined as the ratio of charge to size $(q/r)$.
For the given ions,the hydration energy increases as the charge increases and the ionic radius decreases.
Comparing the ions: $Na^{+}$ ($+1$ charge),$Mg^{2+}$ ($+2$ charge),$Be^{2+}$ ($+2$ charge,smaller radius than $Mg^{2+}$),$Al^{3+}$ ($+3$ charge),and $Cr^{3+}$ ($+3$ charge).
Since $Na^{+}$ has a lower charge $(+1)$ than $Mg^{2+}$ $(+2)$ and a larger ionic radius,the hydration energy of $Mg^{2+}$ is larger than that of $Na^{+}$.

(A) The correct answer is $IIA$ (Alkaline Earth Metals).
In group $IIA$,all elements $(Be, Mg, Ca, Sr, Ba, Ra)$ are metals.
In group $IIIA$,$B$ is a metalloid.
In group $IVA$,$C$ is a non-metal and $Si, Ge$ are metalloids.
In group $VIIA$,$F, Cl$ are non-metals.

(C) The alkaline earth metals belong to Group $2$ of the periodic table.
These elements have a general valence shell electronic configuration of $ns^2$.
Among the given options,$Mg$ (Magnesium),$Ba$ (Barium),and $Ca$ (Calcium) all belong to Group $2$.
Therefore,the correct group is $Mg, Ba, Ca$.

(D) $Beryllium$ $(Be)$ shows a diagonal relationship with $Aluminium$ $(Al)$.
This is due to their similar ionic radii and similar charge-to-size ratio (polarising power).

(B) The solubility of alkaline earth metal carbonates decreases down the group.
This is because the hydration energy of the cation decreases more rapidly than the lattice energy as the size of the cation increases down the group.
Since the hydration energy is not sufficient to overcome the lattice energy,the solubility decreases.
Therefore,the correct option is $(b)$.

(D) The basicity of metal hydroxides increases as we move down the group in the periodic table due to the increase in metallic character and the decrease in ionization energy.
Since $Be, Mg, Ca,$ and $Ba$ belong to Group $2$ (alkaline earth metals),the order of basicity is $Be(OH)_2 < Mg(OH)_2 < Ca(OH)_2 < Ba(OH)_2$.
Therefore,$Ba(OH)_2$ is the most basic hydroxide among the given options.

(D) The reactivity of alkaline earth metals increases as we move down the group due to the decrease in ionization enthalpy.
Among the given elements ($Mg$,$Ca$,$Sr$,$Ba$),$Ba$ is at the bottom of the group.
Therefore,$Ba$ is the most reactive element.

(C) Beryllium $(Be)$ and aluminium $(Al)$ show a diagonal relationship due to similar ionic potential.
However,they differ in their maximum covalency.
Beryllium has a maximum covalency of $4$ because it has only $2s$ and $2p$ orbitals available for bonding.
Aluminium has a maximum covalency of $6$ because it has vacant $3d$ orbitals available for bonding.

(D) The correct answer is $(D)$.
Both $Be(OH)_2$ and $Zn(OH)_2$ are amphoteric in nature,meaning they can react with both acids and bases.

(C) The hydrides of Group $2$ elements,specifically $BeH_2$ and $MgH_2$,exhibit significant covalent character due to the small size and high polarizing power of $Be^{2+}$ and $Mg^{2+}$ ions.
Therefore,both $(a)$ and $(b)$ are correct.

(A) When $BaSO_4$ and $Na_2CO_3$ are fused,a double decomposition reaction occurs to form $BaCO_3$ and $Na_2SO_4$.
The chemical equation is:
$BaSO_4 + Na_2CO_3 \rightarrow BaCO_3 + Na_2SO_4$

(A) Alkaline earth metals $(ns^2)$ are denser than alkali metals $(ns^1)$ because they have two valence electrons available for metallic bonding,which results in stronger metallic bonding compared to alkali metals $(ns^1)$.

(D) The given compound $X$ is $CaCO_3$. The reactions are as follows:
$1. \ CaCO_3 \xrightarrow{\Delta} CaO + CO_2 \uparrow$ ($X$ decomposes to residue $CaO$ and $CO_2$)
$2. \ CaO + H_2O \to Ca(OH)_2$ ($Y$ is calcium hydroxide)
$3. \ Ca(OH)_2 + 2CO_2 \to Ca(HCO_3)_2$ ($Z$ is a clear solution of calcium bicarbonate)
$4. \ Ca(HCO_3)_2 \xrightarrow{\Delta} CaCO_3 \downarrow + CO_2 \uparrow + H_2O$ (Boiling $Z$ reforms $X$)

(A) Slaked lime,$Ca(OH)_2$,is primarily used in the manufacture of cement,where it is mixed with clay and other materials to form clinker.

(D) The chemical formula for Plaster of Paris is $CaSO_4 \cdot \frac{1}{2}H_2O$,which is also written as $(CaSO_4)_2 \cdot H_2O$.
Therefore,the correct option is $(D)$.

(B) The chemical formula for Dolomite is $MgCO_3 \cdot CaCO_3$,which contains both magnesium and calcium ions.
Magnesite is $MgCO_3$.
Carnallite is $KCl \cdot MgCl_2 \cdot 6H_2O$.
Phosphorite is $Ca_3(PO_4)_2$.

(D) Epsom salt is the common name for magnesium sulfate heptahydrate,which has the chemical formula $MgSO_4 \cdot 7H_2O$.

(D) The setting of Plaster of Paris is an exothermic process.
The chemical reaction is: $CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$ (Gypsum).
This process involves the hydration of calcium sulfate hemihydrate to form calcium sulfate dihydrate (Gypsum),which is a harder crystalline structure.

(A) The correct answer is $A$.
$MgCO_3$ is a carbonate of an alkaline earth metal,which decomposes on heating to form the metal oxide and carbon dioxide: $MgCO_3 \xrightarrow{\Delta} MgO + CO_2$.
Alkali metal carbonates like $Na_2CO_3$,$K_2CO_3$,and $Rb_2CO_3$ are thermally stable and do not decompose upon heating.

(A) Alkaline earth metals belong to Group $2$ of the periodic table.
Their valence shell electronic configuration is $ns^2$,where $n$ represents the outermost principal quantum number.

(A) According to Fajan's rule,the ionic character of a bond depends on the polarizability of the cation.
Smaller cations with high charge density have a greater tendency to polarize the anion,leading to increased covalent character.
Among the given metals,$Be^{2+}$ has the smallest ionic radius and the highest charge density.
Therefore,$BeCl_2$ exhibits the most covalent character and is the least ionic among the chlorides of these alkaline earth metals.

(A) $CaF_2$ is commonly known as fluorspar.

(A) Barytes is the mineral form of barium sulfate $(BaSO_4)$.
It is the primary ore of barium.

(D) The solubility of alkaline earth metal sulphates decreases down the group from $Be$ to $Ba$.
This is because the hydration energy decreases more rapidly than the lattice energy as the size of the cation increases.
Since $Be^{2+}$ is the smallest ion,it has the highest hydration energy,which compensates for its lattice energy,making $BeSO_4$ the most soluble.
The order of solubility is: $BeSO_4 > MgSO_4 > CaSO_4 > SrSO_4 > BaSO_4$.

(C) Gypsum is a naturally occurring mineral composed of calcium sulfate dihydrate.
Its chemical formula is $CaSO_4 \cdot 2H_2O$.

(C) Mortar is a building material used to bind bricks or stones together. It is prepared by mixing slaked lime $(Ca(OH)_2)$,sand,and water.

(B) When gypsum $(CaSO_4 \cdot 2H_2O)$ is heated to $120 \, ^oC$ $(393 \, K)$,it loses three-fourths of its water of crystallization to form Plaster of Paris.
The chemical reaction is: $2(CaSO_4 \cdot 2H_2O) \xrightarrow{120 \, ^oC} 2CaSO_4 \cdot H_2O + 3H_2O$.
Thus,the correct composition is $2CaSO_4 \cdot H_2O$.

(B) Beryllium is a highly reactive metal,and its isolation presents several difficulties. $BeCl_2$ is covalent and has a low melting point,making it a poor conductor of electricity. Therefore,it is mixed with $NaCl$ to increase its electrical conductivity and lower the melting point. The mixture is then subjected to electrolysis to obtain pure beryllium.

(D) The hydrated magnesium chloride $(MgCl_2 \cdot 6H_2O)$ undergoes hydrolysis when heated directly,forming $MgO$.
To obtain pure anhydrous $MgCl_2$,the hydrated salt is heated to red heat in a stream of $HCl$ gas.
The $HCl$ gas shifts the equilibrium to the left,preventing the hydrolysis of $MgCl_2$ into $MgO$ and $HCl$.

(A) The correct answer is $A$.
Strontium salts impart a crimson or deep pink colour to the flame due to the excitation of electrons in $Sr^{2+}$ ions.

(A) Calcium salts impart a characteristic $Brick \ Red$ colour to the flame during the flame test.

(B) Magnesia is the common name for magnesium oxide,which has the chemical formula $MgO$.

(B) The mixture of $MgCl_2$ and $MgO$ (often with water) is known as Sorel cement or Magnesia cement.
The reaction is: $MgCl_2 \cdot 6H_2O + 5MgO + xH_2O \to MgCl_2 \cdot 5MgO \cdot xH_2O$ (Magnesia cement or Sorel cement).

(D) As we move down the group,the electropositive character increases because the ionization energy $(I.E.)$ decreases.
$Ba$ is the most electropositive element in the group.

(C) The correct answer is $(C)$. The solubility order is $BeSO_4 > MgSO_4 > CaSO_4 > SrSO_4 > BaSO_4$.
As we move down the group from $Be$ to $Ba$,the size of the cation increases.
The lattice energy remains almost constant because the sulphate ion is very large compared to the cations,so the change in cation size has a negligible effect on the lattice energy.
However,the hydration energy decreases significantly from $Be^{2+}$ to $Ba^{2+}$ due to the increase in ionic radius.
Since hydration energy is the driving force for solubility,the decrease in hydration energy leads to a decrease in the solubility of sulphates down the group.

(A) The first ionization potential $(I.E.)$ of alkaline earth metals decreases down the group as the atomic size increases and the valence electrons are further from the nucleus.
The order of decreasing first ionization potential for the given elements is $Mg > Ca > Sr > Ba$.

Element	$I.E.$ $(kJ \ mol^{-1})$
$Mg$	$737$
$Ca$	$590$
$Sr$	$549$
$Ba$	$503$

(A) $Be$ (Beryllium) shows a diagonal relationship with $Al$ (Aluminium) due to their similar ionic potential (charge/size ratio).
This results in similar chemical properties,such as the amphoteric nature of their oxides and hydroxides.

(D) . Duralumin ($Al = 95\%$,$Cu = 4\%$,$Mn = 0.5\%$,$Mg = 0.5\%$) is a light,tough,and durable alloy.
Due to these properties,it is extensively used in the manufacture of aeroplane parts and automobile components.

(C) The green flame in fireworks is produced due to the presence of Barium $(Ba)$ salts.

Element	Flame Colour
$Na$	Golden Yellow
$K$	Pale Violet
$Ba$	Apple Green
$Ca$	Brick Red

(C) Bone ash is the white residue obtained after burning bones.
It primarily consists of calcium phosphate,which is represented by the formula $Ca_3(PO_4)_2$.
While raw bone contains hydroxyapatite,$Ca_3(OH)(PO_4)_3$,the calcination process converts it into the stable form $Ca_3(PO_4)_2$.

(B) $CaO$ (Calcium oxide) is a basic oxide that absorbs $CO_2$ to form $CaCO_3$.
$CaO + CO_2 \to CaCO_3$
It also reacts violently with water to form calcium hydroxide,releasing a large amount of heat.
$CaO + H_2O \to Ca(OH)_2 + \text{Heat}$

(B) $CaO$ is known as quick lime.
$Ca(OH)_2$ is known as slaked lime.
An aqueous suspension of $Ca(OH)_2$ in water is called lime water.
$CaCO_3$ is known as lime stone.