Alkaline earth metals Questions in English

(N/A) The solubility of sulphates of group $2$ elements depends on the balance between their hydration enthalpy and lattice enthalpy.
As we move down the group,the size of the metal cation increases,which leads to a significant decrease in the hydration enthalpy.
The lattice energy of these sulphates remains relatively constant.
For $BeSO_4$ and $MgSO_4$,the hydration enthalpy is very high,which is sufficient to overcome the lattice enthalpy,making them readily soluble in water.
In contrast,for $CaSO_4, SrSO_4$ and $BaSO_4$,the hydration enthalpy is not high enough to overcome the lattice enthalpy,resulting in their insolubility in water.

(N/A) Except $Be$ and $Mg$,all alkaline earth metals impart characteristic colours to the flame of a Bunsen burner.
These two metals have very small atomic radii,and their electrons are more strongly bound due to a high effective nuclear charge.
The energy provided by the Bunsen flame is not sufficient to excite these electrons to higher energy levels.
Hence,these elements do not impart any colour to the flame.

(A) $A-3, B-4, C-2, D-1$
$A$. $CaCO_3$: Specially precipitated $CaCO_3$ is used in the manufacture of high quality paper.
$B$. $Ca(OH)_2$: It is used in white washing due to its disinfectant nature and being sparingly soluble in water.
$C$. $CaO$: It is used in the manufacture of $Na_2CO_3$ from $NaOH$.
$D$. $CaSO_4$: It is used in dentistry and ornamental work.

(A) Compound $(A)$ is $CaO$ (Calcium oxide). When water is added to it,it forms compound $(B)$,which is $Ca(OH)_2$ (Calcium hydroxide or lime water).
$(i)$ $CaO + H_2O \rightarrow Ca(OH)_2$
When $CO_2$ is passed through $(B)$,it forms $CaCO_3$ (Calcium carbonate),which is compound $(C)$ and is insoluble in water,causing the solution to turn milky.
$(ii)$ $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$
When excess $CO_2$ is passed,$CaCO_3$ reacts with $CO_2$ and water to form $Ca(HCO_3)_2$ (Calcium bicarbonate),which is compound $(D)$. Since $Ca(HCO_3)_2$ is soluble in water,the milkiness disappears.
$(iii)$ $CaCO_3 + CO_2 + H_2O \rightarrow Ca(HCO_3)_2$

(N/A) In group $2$,$Be$ is the only element that forms a covalent oxide $BeO$,which is amphoteric in nature. The other elements of this group form ionic oxides which are basic in nature. $BeO$ reacts with water to form $Be(OH)_{2}$,which is an amphoteric hydroxide.
$BeO + H_{2}O \rightarrow Be(OH)_{2}$
$Be(OH)_{2}$ is amphoteric,meaning it reacts with both acids and bases.
Reaction with an alkali $(NaOH)$:
$2 NaOH_{(aq)} + Be(OH)_{2(s)} \rightarrow Na_{2}[Be(OH)_{4}]_{(aq)}$
(Sodium tetrahydroxoberyllate)
Reaction with an acid $(H_{2}SO_{4})$:
$Be(OH)_{2(s)} + H_{2}SO_{4(aq)} \rightarrow BeSO_{4(aq)} + 2 H_{2}O_{(l)}$
(Beryllium sulphate)

(B) The alkaline earth metal $Be$ (Beryllium) forms $BeSO_{4}$,which is water-soluble due to high hydration energy.
$Be(OH)_{2}$ is amphoteric and water-insoluble.
$BeO$ is very stable to heat and possesses a wurtzite structure,not a rock-salt structure.
Therefore,the correct metal is $Be$.

(A) The solubility of alkaline earth metal sulphates decreases down the group due to the decrease in hydration enthalpy being more significant than the decrease in lattice enthalpy.
The order of solubility is: $BeSO_4 > MgSO_4 > CaSO_4 > SrSO_4 > BaSO_4$.
Both $BeSO_4$ and $MgSO_4$ have high solubility in water compared to the other sulphates in the group.

(A) The purpose of adding gypsum $(CaSO_{4} \cdot 2H_{2}O)$ to cement is to retard or slow down the initial setting process of the cement.
This allows the cement to remain in a plastic state for a longer duration,ensuring it can be properly placed and hardened without forming cracks.

(A) The solubility of alkaline earth metal fluorides is determined by the balance between lattice energy and hydration energy.
For small cations like $Be^{2+}$,the hydration energy is significantly higher than the lattice energy,making $BeF_{2}$ highly soluble in water.
As the size of the cation increases from $Be^{2+}$ to $Sr^{2+}$,the hydration energy decreases more rapidly than the lattice energy,leading to a decrease in solubility.
Therefore,$BeF_{2}$ has the maximum solubility among the given compounds.

(B) Statement $I$ is false because while $CaCl_2 \cdot 6H_2O$ can be dehydrated to anhydrous $CaCl_2$ by heating,$MgCl_2 \cdot 8H_2O$ (or $6H_2O$) undergoes hydrolysis upon heating to form $MgO$ and $HCl$ due to the high polarizing power of $Mg^{2+}$.
Statement $II$ is false because $BeO$ is indeed amphoteric,but the oxides of other elements in Group $2$ $(MgO, CaO, SrO, BaO)$ are basic,not acidic.

(C) $Ca(OCl)_2$ is used as a bleaching agent $(iii)$.
$CaSO_4 \cdot \frac{1}{2} H_2O$ is known as Plaster of Paris $(iv)$.
$CaO$ is a major component in the manufacturing of cement $(ii)$.
$CaCO_3$ is used as an antacid $(i)$.
Therefore,the correct matching is $a-iii, b-iv, c-ii, d-i$.

(A) . $Be$ is used in the windows of $X$-ray tubes.
$b$. $Mg$ is used in incendiary bombs and signals.
$c$. $Ca$ is used in the extraction of metals (as a reducing agent).
$d$. $Ra$ is used in the treatment of cancer (radiotherapy).
Therefore,the correct matching is $a-iv, b-iii, c-ii, d-i$.

(B) When $CO_{2}$ is passed through slaked lime $(Ca(OH)_{2})$,it first forms a white precipitate of calcium carbonate $(CaCO_{3})$:
$Ca(OH)_{2} + CO_{2} \longrightarrow CaCO_{3} \downarrow + H_{2}O$
When excess $CO_{2}$ is passed,the calcium carbonate reacts further to form soluble calcium bicarbonate $(Ca(HCO_{3})_{2})$:
$CaCO_{3} + CO_{2} + H_{2}O \longrightarrow Ca(HCO_{3})_{2}$

(A) Assertion $A$ is true: $BaCO_3$ is insoluble in water due to high lattice energy and is thermally stable.
Reason $R$ is true: As the size of the alkaline earth metal cation increases down the group $(Be^{2+} < Mg^{2+} < Ca^{2+} < Sr^{2+} < Ba^{2+})$,the polarising power of the cation decreases,which leads to an increase in the thermal stability of the corresponding carbonates.
Since $Ba^{2+}$ is the largest cation in the group,$BaCO_3$ is the most thermally stable carbonate among them.
Therefore,$R$ is the correct explanation for $A$.

(D) The chemical formula for gypsum is $CaSO_4 \cdot 2H_2O$,which contains $2$ water molecules.
The chemical formula for dead burnt plaster is $CaSO_4$,which contains $0$ water molecules.
The chemical formula for plaster of paris is $CaSO_4 \cdot \frac{1}{2}H_2O$,which contains $0.5$ water molecules.
Therefore,the number of water molecules are $2, 0$ and $0.5$ respectively.

(D) According to Fajan's rule,covalent character is directly proportional to the polarising power of the cation.
Polarising power is inversely proportional to the size of the cation $(Polarising \ power \propto \frac{1}{\text{size of cation}})$.
Among the given alkaline earth metal ions,the size order is $Be^{2+} < Mg^{2+} < Ca^{2+} < Sr^{2+}$.
Since $Be^{2+}$ has the smallest size,it has the highest polarising power,making $BeCl_2$ the most covalent compound.
Due to its covalent nature,$BeCl_2$ is soluble in organic solvents.

(C) Statement-$I$ is incorrect because $Be(OH)_2$ is amphoteric in nature and dissolves in alkali to form beryllates.
Statement-$II$ is correct because the solubility of alkaline earth metal hydroxides in water increases down the group as the lattice energy decreases more rapidly than the hydration energy.
Therefore,Statement-$I$ is incorrect and Statement-$II$ is correct.

(D) In aqueous solutions,the ionic mobility is inversely proportional to the degree of hydration.
Smaller ions have a higher charge density,leading to a larger hydration shell,which decreases their mobility.
Among the given ions,$Be^{2+}$ is the smallest and has the highest hydration energy,resulting in the largest hydrated radius and lowest mobility.
Conversely,$Sr^{2+}$ is the largest among the options,has the smallest hydration shell,and therefore exhibits the highest ionic mobility.

(D) The flame test is used to identify elements based on the characteristic color they impart to the flame.
$Li$ (Lithium) gives a crimson red color.
$Na$ (Sodium) gives a golden yellow color.
$Rb$ (Rubidium) gives a red-violet color.
$Be$ (Beryllium) and $Mg$ (Magnesium) do not impart any characteristic color to the flame because their ionization energy is very high,and the energy of the flame is not sufficient to excite their electrons to higher energy levels.
Therefore,$Be$ cannot be confirmed by the flame test.

(D) The melting points of alkaline earth metals do not show a regular trend due to differences in their crystal structures.
The melting points are as follows:
$Be: 1560 \ K$
$Mg: 924 \ K$
$Ca: 1124 \ K$
$Sr: 1062 \ K$
Comparing these values,the correct order is $Be > Ca > Sr > Mg$.

(C) The reaction is as follows:
$BeO + 2HF + 2NH_3 \rightarrow (NH_4)_2[BeF_4]$
Here,$[A]$ is $(NH_4)_2[BeF_4]$.
In the complex ion $[BeF_4]^{2-}$,let the oxidation state of $Be$ be $x$.
$x + 4(-1) = -2$
$x - 4 = -2$
$x = +2$
Thus,the oxidation state of $Be$ in $[A]$ is $2$.

(C) $2 BeCl_2 + LiAlH_4 \rightarrow 2 BeH_2 + LiCl + AlCl_3$
This reaction is a standard laboratory method for the preparation of beryllium hydride $(BeH_2)$.

(C) $SO_{3}$ and $SiO_{2}$ are acidic oxides.
$CaO$ is a basic oxide because it is an oxide of an alkaline earth metal.
$Al_{2}O_{3}$ is an amphoteric oxide.

(C) In the $IIA$ group (alkaline earth metals),the density decreases from $Be$ to $Ca$ and then increases from $Ca$ to $Ba$.
The densities of these elements are: $Be (1.85 \ g/cm^3)$,$Mg (1.74 \ g/cm^3)$,$Ca (1.55 \ g/cm^3)$,and $Sr (2.63 \ g/cm^3)$.
Therefore,the correct order of density is $Sr > Be > Mg > Ca$.

(B) The reaction between $BeCl_{2}$ and $LiAlH_{4}$ is a common method for the preparation of beryllium hydride $(BeH_{2})$.
The balanced chemical equation is:
$2BeCl_{2} + LiAlH_{4} \rightarrow 2BeH_{2} + LiCl + AlCl_{3}$
Thus,the products formed are $BeH_{2}$,$LiCl$,and $AlCl_{3}$,which correspond to options $(B)$,$(D)$,and $(A)$.

(B) Gypsum $(CaSO_{4} \cdot 2 H_{2}O)$ is added to Portland cement to slow down the process of setting,thereby increasing the setting time.

(B) $ (b) $
The most abundant metal ion present in the human body is $Ca^{2+}$.
This essential mineral is required in large quantities and makes up approximately $1.2\, \%$ of the human body mass,with more than $99\, \%$ found in bones and teeth.

(A) The thermal stability of alkaline earth metal carbonates increases as we move down the group from $Mg$ to $Ba$.
This is because the electropositive character of the metal increases down the group,which leads to a stronger ionic bond between the metal cation and the carbonate anion.
Consequently,more energy is required to decompose the carbonate into the metal oxide and carbon dioxide.
Therefore,the correct order of thermal stability is $BaCO_{3} > SrCO_{3} > CaCO_{3} > MgCO_{3}$.

(D) The correct option is $D$.
When $CO_2$ is passed through lime water $(Ca(OH)_2)$,it initially turns milky due to the formation of insoluble calcium carbonate $(CaCO_3)$:
$Ca(OH)_2 + CO_2 \rightarrow CaCO_3 \downarrow + H_2O$
On continuous bubbling of $CO_2$,the milky precipitate dissolves to form soluble calcium bicarbonate $(Ca(HCO_3)_2)$,making the solution clear:
$CaCO_3 + CO_2 + H_2O \rightarrow Ca(HCO_3)_2(aq)$

(A) The reaction of beryllium oxide $(BeO)$ with ammonia $(NH_3)$ and hydrogen fluoride $(HF)$ is a standard method for the preparation of ammonium tetrafluoroberyllate.
The balanced chemical equation is: $BeO + 2 NH_3 + 4 HF \rightarrow (NH_4)_2BeF_4 + H_2O$.
Upon thermal decomposition,$(NH_4)_2BeF_4$ breaks down into beryllium fluoride $(BeF_2)$ and ammonium fluoride $(NH_4F)$: $(NH_4)_2BeF_4 \xrightarrow{\Delta} BeF_2 + 2 NH_4F$.
Therefore,'$A$' is $(NH_4)_2BeF_4$.

(B) The reduction potential of an element is determined by the sum of its sublimation energy,ionization energy,and hydration energy.
$Be$ has a very high atomization (sublimation) enthalpy and high ionization energy due to its small size,which makes its reduction potential less negative compared to other alkaline earth metals $(AEM)$.
Although $Be^{2+}$ has a very high hydration energy due to its small size,the high energy required for atomization and ionization dominates,resulting in a less negative reduction potential.
Therefore,both Assertion $A$ and Reason $R$ are correct,and $R$ provides the correct explanation for $A$.

(C) 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.
$BeSO_4$ and $MgSO_4$ have very high hydration energies,which compensate for their lattice energies,making them readily soluble in water.
Therefore,$(A)$ and $(B)$ are the correct choices.

(D) The chlorides of alkaline earth metals generally show ionic character,but $BeCl_2$ is an exception.
Due to the small size and high polarizing power of the $Be^{2+}$ ion,$BeCl_2$ exhibits significant covalent character.
According to the principle of 'like dissolves like',covalent compounds are soluble in organic solvents.
Therefore,$BeCl_2$ is soluble in organic solvents.

(B) $Ca^{2+}$ ions play a significant role in neuromuscular function,interneuronal transmission,and cell membrane integrity.
They are essential for the release of neurotransmitters at the synaptic junction.

(B) $A.$ Beryllium oxide $(BeO)$ is amphoteric in nature, not purely acidic.
$B.$ Beryllium carbonate $(BeCO_3)$ is thermally unstable and decomposes easily, so it is kept in an atmosphere of $CO_2$ to prevent decomposition.
$C.$ Beryllium sulphate $(BeSO_4)$ is readily soluble in water due to the high hydration enthalpy of the small $Be^{2+}$ ion.
$D.$ Beryllium shows anomalous behavior compared to other alkaline earth metals due to its small atomic size, high ionization energy, and high polarising power $(\phi)$.
Therefore, statements $B, C,$ and $D$ are correct.

(D) The setting time of cement is increased by adding $Gypsum$ $(CaSO_4 \cdot 2H_2O)$. It acts as a retarder,which slows down the hydration process of tricalcium aluminate $(C_3A)$,thereby preventing the cement from setting too quickly.

(A) Hydration enthalpy is inversely proportional to the ionic size: $\text{Hydration Enthalpy} \propto \frac{1}{\text{size}}$.
As we move down the group,the ionic size increases,which causes the hydration enthalpy to decrease.
The order of hydration enthalpy for alkaline earth metal ions is: $Be^{2+} > Mg^{2+} > Ca^{2+} > Sr^{2+} > Ba^{2+}$.
Therefore,$Be^{2+}$ has the highest hydration enthalpy.

(C) When water is added to cement,it sets very quickly,which makes it difficult to work with. Adding a small amount of gypsum $(CaSO_4 \cdot 2H_2O)$ to the cement clinker during the grinding process helps to retard or slow down the initial setting time of the cement,allowing sufficient time for mixing,placing,and finishing the concrete.

(B) The reaction of quick lime $(CaO)$ with water is exothermic and produces slaked lime $(Ca(OH)_{2})$,which is '$A$'.
$CaO + H_{2}O \rightarrow Ca(OH)_{2}$
When $CO_{2}$ is passed through an aqueous solution of '$A$' $(Ca(OH)_{2})$,it forms a white precipitate of calcium carbonate $(CaCO_{3})$,which is '$B$'.
$Ca(OH)_{2} + CO_{2} \rightarrow CaCO_{3} + H_{2}O$
Further reaction of $CaCO_{3}$ with $CO_{2}$ and water leads to the formation of soluble calcium bicarbonate $(Ca(HCO_{3})_{2})$.
$CaCO_{3} + H_{2}O + CO_{2} \rightarrow Ca(HCO_{3})_{2}$
Therefore,'$A$' is slaked lime.

(A) $Mg(NO_3)_2$ crystallizes as a hexahydrate,$Mg(NO_3)_2 \cdot 6H_2O$,so $X = 6$.
$Ba(NO_3)_2$ crystallizes as an anhydrous salt,so $Y = 0$.
Therefore,the sum $X + Y = 6 + 0 = 6$.

(C) The reaction between $CaCl_2$ and $Na_2CO_3$ is a double displacement reaction:
$CaCl_2 + Na_2CO_3 \rightarrow CaCO_3(s) + 2NaCl(aq)$
Comparing this with the given reaction $CaCl_2 + Na_2CO_3 \rightarrow X + Y$,we identify $X$ as $CaCO_3$ and $Y$ as $NaCl$.
To convert $CaCO_3$ back to $CaCl_2$,it is reacted with hydrochloric acid $(HCl)$:
$CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$
Thus,$Z$ is $HCl$.
Therefore,$X = CaCO_3$,$Y = NaCl$,and $Z = HCl$.

(D) $Be(OH)_2$ is amphoteric in nature,while $Sr(OH)_2$ is basic in nature.
These two undergo an acid-base neutralization reaction to form the salt $Sr[Be(OH)_4]$.
In this salt,$Sr^{2+}$ is the cation and $[Be(OH)_4]^{2-}$ is the complex anion.
Therefore,$Be$ is present in the anionic part of the salt,not the cationic part.
Thus,option $D$ is the incorrect statement.

(A) According to the $NCERT$ chemistry textbook for $s$-block elements,the thermal decomposition of ammonium tetrafluoroberyllate is the preferred method for the preparation of pure $BeF_2$.
The reaction is given as:
$(NH_4)_2BeF_4 \xrightarrow{\Delta} BeF_2 + 2NH_4F$

(B) The electrons in $Be$ and $Mg$ are strongly bound to the nucleus due to their small size and high ionization enthalpy.
Consequently,the energy required to excite these electrons to higher energy levels is very high,which cannot be provided by the heat of a Bunsen flame.
Therefore,$Be$ and $Mg$ do not impart any characteristic color to the flame.
Assertion $(A)$ is false because $BeCl_2$ and $MgCl_2$ do not produce a characteristic flame.
Reason $(R)$ is true because the excitation energy for $Be$ and $Mg$ is indeed very high.

(A) The thermal stability of alkaline earth metal sulfates increases down the group as the size of the cation increases,which decreases the polarizing power of the cation on the sulfate anion.
Therefore,the correct order of thermal stability is $BeSO_4 < MgSO_4 < CaSO_4 < SrSO_4 < BaSO_4$.
Option $A$ is correct.

(C) $Ra$ $(Radium)$ is a radioactive element that has been historically used in radiotherapy for the treatment of cancer.
Its isotopes emit radiation that can destroy cancerous cells.

(B) Amphoteric oxides are those that react with both acids and bases to form salt and water.
Among the given options,$BeO$ (Beryllium oxide) is amphoteric in nature.
$MgO$,$BaO$,and $Li_2O$ are basic oxides.

(A) When carbon dioxide is bubbled through a solution of calcium hydroxide (slaked lime),a water-insoluble solid,calcium carbonate,is formed.
The chemical reaction is:
$Ca(OH)_{2(aq)} + CO_{2(g)} \rightarrow CaCO_{3(s)} + H_2O_{(l)}$

(A) The elements in Group $2$ of the periodic table,known as alkaline earth metals,typically exhibit a common oxidation state of $+2$.
Among the given options,$Sr$ (Strontium) belongs to Group $2$.
$Rb$ (Rubidium),$Na$ (Sodium),and $Li$ (Lithium) belong to Group $1$ (alkali metals) and typically exhibit an oxidation state of $+1$.

(D) $Barium$ $(Ba)$ is an alkaline earth metal,which forms a basic oxide $(BaO)$.
Non-metals like $Carbon$ $(CO_2)$,$Phosphorus$ $(P_4O_{10})$,and $Chlorine$ $(Cl_2O_7)$ form acidic oxides.