Alkali metals Questions in English

(B) In an aqueous solution,the electrical conductivity depends on the ionic mobility of the hydrated ions.
Smaller ions have a higher charge density,leading to greater hydration,which increases their effective size and decreases their mobility.
Among the alkali metal ions,$Li^+$ has the smallest ionic radius,so it is most heavily hydrated,resulting in the lowest mobility.
$Cs^+$ has the largest ionic radius,so it is the least hydrated,resulting in the highest mobility and the highest electrical conductivity.

(C) The anomalous properties of $Li$ arise due to its small size and high polarizing power. $Li$ is actually the hardest among group-$1$ metals,not the softest. Therefore,the statement that $Li$ is a much softer metal compared to other group-$1$ metals is incorrect and represents a property that is not anomalous (because it is false). All other options listed are recognized anomalous properties of $Li$.

(A) Alkali metals are highly reactive and react violently with water to produce hydrogen gas,which is flammable. Therefore,water cannot be used. $CCl_4$ (Carbon tetrachloride) is used to extinguish fires caused by alkali metals because it does not react with them.

(A) When sodium metal is heated in a stream of dry ammonia at $573 \ K$,it forms sodium amide $(NaNH_2)$ and releases hydrogen gas.
The chemical equation is: $2Na + 2NH_3 \to 2NaNH_2 + H_2$.

(C) In an aqueous solution,the ionic mobility depends on the size of the hydrated ion.
$Li^+$ has the smallest ionic radius,which leads to the highest degree of hydration.
Due to the formation of a large hydrated shell,the effective size of the hydrated $Li^+$ ion is the largest among alkali metal ions.
Therefore,$Li^+$ moves the slowest in an aqueous solution,resulting in the lowest ionic mobility.

(D) An excess of $Na^+$ ions in the human body leads to high blood pressure (hypertension).

(C) $Al(OH)_3$,$Pb(OH)_2$,and $Zn(OH)_2$ are amphoteric in nature,therefore they dissolve in basic $NaOH$ solution.
However,$Fe(OH)_3$ is basic in nature and does not dissolve in $NaOH$ solution.

(B) The ionization energy of Group $1$ elements decreases as we move down the group. This is because the atomic size increases and the valence electron becomes farther from the nucleus,resulting in a weaker electrostatic attraction.

(A) The ionic conductivity in an aqueous solution depends on the degree of hydration of the ions.
Smaller cations have a higher charge density,leading to a higher degree of hydration,which increases their effective size and decreases their mobility.
The order of hydration is: $Li^+ > Na^+ > K^+ > Rb^+$.
Since higher hydration leads to lower ionic mobility,the order of ionic conductivity is: $Li^+ < Na^+ < K^+ < Rb^+$.

(C) $Li$ is the strongest reducing agent among alkali metals because the $Li^+$ ion has the highest hydration energy.

(A) All alkali metal nitrates (except $LiNO_3$) decompose upon strong heating to produce the corresponding nitrite and $O_2$.
$2KNO_3 \to 2KNO_2 + O_2$
In contrast,nitrates of heavy metals (like $Pb$,$Ca$,$Ag$) decompose to produce metal oxides,nitrogen dioxide $(NO_2)$,and oxygen $(O_2)$:
$2Pb(NO_3)_2 \to 2PbO + 4NO_2 + O_2$
$2Ca(NO_3)_2 \to 2CaO + 4NO_2 + O_2$
$2AgNO_3 \to 2Ag + 2NO_2 + O_2$
Since $KNO_3$ produces only $KNO_2$ and $O_2$,it does not produce $NO_2$.

(D) Glauber's salt is the common name for sodium sulfate decahydrate.
Its chemical formula is $Na_2SO_4 \cdot 10H_2O$.

(B) The metallic luster of metals is explained by the oscillations of free (loose) electrons present in the metallic lattice when they interact with light.

(B) Sodium nitrate $(NaNO_3)$ decomposes upon heating.
At temperatures above ${800\,^o}C$,the reaction is:
$2NaNO_3 \xrightarrow{> 800\,^o C} 2NaNO_2 + O_2$
Thus,the gaseous product formed is oxygen $(O_2)$.

(C) Lithium directly reacts with nitrogen to form lithium nitride,which reacts with water to produce $NH_3$.
$6Li + N_2 \to 2Li_3N$
$Li_3N + 3H_2O \to 3LiOH + NH_3$
Passing the produced $NH_3$ into $CuSO_4$ solution forms the tetraamminecopper$(II)$ complex,which is deep blue in color.
$CuSO_4 + 4NH_3 \to [Cu(NH_3)_4]SO_4$

(A) Alkali metals like sodium,potassium,and lithium are highly reactive and react violently with water $(H_2O)$ and carbon dioxide $(CO_2)$.
They can react with $CO_2$ to form carbonates,which does not effectively extinguish the fire.
Water reacts to produce hydrogen gas $(H_2)$,which is flammable and can cause explosions.
Therefore,an asbestos blanket is used to cut off the oxygen supply and extinguish the fire.

(A) When sodium bicarbonate $(NaHCO_3)$ is heated strongly,it undergoes thermal decomposition to form sodium carbonate $(Na_2CO_3)$,water $(H_2O)$,and carbon dioxide $(CO_2)$.
The balanced chemical equation is:
$2NaHCO_3 \to Na_2CO_3 + H_2O + CO_2$

(D) Lithium salts are the least conducting in their aqueous solutions compared to other alkali metal salts because the $Li^+$ ion has a very high degree of hydration.
Due to its small size,the $Li^+$ ion gets heavily hydrated,which increases its effective size and decreases its ionic mobility,thereby reducing the electrical conductivity of the solution.

(D) Carbonates of alkaline earth metals are sparingly soluble in water,whereas bicarbonates are generally soluble.
Among the given compounds,$CaCO_3$ is a carbonate of an alkaline earth metal and is very poorly soluble.
For alkali metal bicarbonates,solubility increases down the group as the lattice energy decreases more rapidly than the hydration energy.
Therefore,the solubility order is $CaCO_3 < NaHCO_3 < KHCO_3$.

(B) Magnesium is a central metal ion in the structure of chlorophyll,which is the primary pigment responsible for photosynthesis in plants.

(A) When $Mg$ burns in $CO_2$,it reduces $CO_2$ to carbon and forms magnesium oxide. The chemical reaction is: $2Mg(s) + CO_2(g) \rightarrow 2MgO(s) + C(s)$.

(D) Metals that are more reactive than hydrogen in the electrochemical series can displace hydrogen from acids.
Magnesium $(Mg)$ is more reactive than hydrogen,so it reacts with hydrochloric acid $(HCl)$ to release hydrogen gas $(H_2)$.
The chemical reaction is:
$Mg + 2HCl \to MgCl_2 + H_2 \uparrow$

(A) The reactivity and the strength as a reducing agent decrease as we move down the group.
Since $Be$ is less reactive than $Mg$,it cannot displace $Mg$ from its salt solution.
Therefore,$Be$ cannot reduce $Mg^{2+}$ to $Mg$ metal.
Thus,no reaction occurs.

(A) The wire of a flash bulb is made of magnesium $(Mg)$.
When the flash is triggered,the magnesium wire burns rapidly in an oxygen atmosphere to produce a bright flash of light.

(D) $Ca^{2+}$ ions play a crucial role in muscle contraction by binding to troponin,which initiates the interaction between actin and myosin filaments.

(D) Carnallite is an ore of magnesium with the formula $KCl \cdot MgCl_2 \cdot 6H_2O$.
During the electrolysis of fused carnallite,magnesium metal is deposited at the cathode and chlorine gas $(Cl_2)$ is evolved at the anode.

(C) Magnesium is extracted by the electrolysis of molten magnesium salt (a mixture of $MgCl_2$,$NaCl$,and $CaCl_2$).

(C) $Mg(OH)_2$ is used as an antacid. $Mg$ continues to burn in an atmosphere of $CO_2$ because it reduces $CO_2$ to carbon.
The reaction is: $2Mg + CO_2 \to 2MgO + C$.

(C) Magnesium is a strong reducing agent. It reduces $CO_2$ to $C$ (carbon) according to the reaction: $2Mg + CO_2 \rightarrow 2MgO + C$.

(D) The hydration energy of $Mg^{2+}$ is significantly higher than that of $Mg^+$. This large release of energy during the hydration of the divalent ion compensates for the energy required to remove the second electron,making $Mg^{2+}$ the stable form in aqueous solutions.

(C) Dolomite is a sedimentary carbonate rock that contains a high proportion of the mineral dolomite,which is a double carbonate of calcium and magnesium with the chemical formula $CaCO_3 \cdot MgCO_3$.

(A) Very dilute $HNO_3$ (approximately $1\%$ concentration) reacts with $Mg$ and $Mn$ to liberate $H_2$ gas.
The reaction is: $Mg(s) + 2HNO_3(aq) \to Mg(NO_3)_2(aq) + H_2(g) \uparrow$.
$Al$ and $Fe$ become passive due to the formation of an oxide layer,and $Cu$ does not react with dilute $HNO_3$ to produce $H_2$ because $HNO_3$ is an oxidizing agent.

(A) The flame test is used to identify metal ions based on the characteristic color they impart to a Bunsen flame.
$Be^{2+}$ and $Mg^{2+}$ ions do not impart any characteristic color to the flame because the energy of the flame is not sufficient to excite their electrons to higher energy levels.
Among the given options,$Be^{2+}$ is the correct cation that does not show a flame test.

(B) $3Mg + N_2 \xrightarrow{\Delta} Mg_3N_2$ (where $X = Mg$ and $Y = Mg_3N_2$).
$Mg_3N_2 + 6H_2O \to 3Mg(OH)_2 + 2NH_3$ (colorless gas).
$CuSO_4 + 4NH_3 \to [Cu(NH_3)_4]SO_4$ (deep blue complex).

(B) In aqueous solution,the ionic mobility depends on the degree of hydration.
Smaller ions have a higher charge density,which leads to a greater degree of hydration.
$Li^{+}$ is the smallest ion,so it gets heavily hydrated,forming a large hydrated ion $[Li(H_2O)_n]^{+}$,which moves slowly.
$Rb^{+}$ is the largest ion among the given options,so it has the least degree of hydration,resulting in a smaller hydrated ion size.
Therefore,$Rb^{+}$ has the highest ionic mobility in aqueous solution.

(C) In an aqueous medium,alkali metal ions get hydrated. The extent of hydration depends on the size of the ion; smaller ions have higher charge density and get more hydrated.
The order of hydrated ionic radii is: $Li^{+} > Na^{+} > K^{+} > Rb^{+} > Cs^{+}$.
Since the hydrated ion of $Li^{+}$ is the largest,it moves the slowest in an electric field.
Therefore,the correct order of ionic mobility is: $Li^{+} < Na^{+} < K^{+} < Rb^{+}$.

(B) In an aqueous solution,the ionic mobility depends on the size of the hydrated ion.
Smaller ions have a higher charge density,leading to greater hydration (more water molecules attached to them).
Consequently,the hydrated size follows the order: $Na^{+} > K^{+} > Rb^{+} > Cs^{+}$.
Since larger hydrated ions move more slowly through the solvent,the ionic mobility follows the inverse order: $Cs^{+} > Rb^{+} > K^{+} > Na^{+}$.

(D) The thermal stability of alkali metal hydrides decreases as we move from $Li$ to $Cs$ in the group.
This is because the $M-H$ bond strength decreases as the size of the alkali metal cation increases down the group.
Therefore,the correct order of decreasing thermal stability is: $LiH > NaH > KH > RbH > CsH$.

(A) $NaOH$ is a strong alkali. It reacts with acidic and amphoteric oxides to form salts.
$CaO$ is a basic oxide.
Therefore,it does not react with $NaOH$.

(C) The reaction of $Al$ with excess $NaOH$ is: $2Al(s) + 2NaOH(aq) + 6H_2O(l) \to 2Na[Al(OH)_4](aq) + 3H_2(g)$.
Aluminum dissolves in excess $NaOH$ to form soluble sodium tetrahydroxoaluminate$(III)$,not $Al(OH)_3$.
Therefore,the statement in option $C$ is incorrect.

(A) Alkali metal carbonates are generally stable to heat,except for $Li_2CO_3$.
As we move down the group,the electropositive character of the alkali metals increases,which leads to an increase in the thermal stability of their carbonates.
The order of thermal stability is: $Li_2CO_3 < Na_2CO_3 < K_2CO_3 < Rb_2CO_3 < Cs_2CO_3$.
$Li_2CO_3$ is the least stable because $Li^+$ has a high polarizing power due to its small size,which weakens the $C-O$ bond in the carbonate ion,leading to decomposition upon heating: $Li_2CO_3 \rightarrow Li_2O + CO_2$.

(A) Alkali metals have very low ionization enthalpy compared to other elements.
Due to this,the valence electrons in alkali metals can be easily excited to higher energy levels by the heat of the flame.
When these excited electrons return to the ground state,they emit radiation in the visible region,which imparts a characteristic color to the flame.

(C) The stability of superoxides increases with an increase in the size of the alkali metal cation and its electropositive character.
As the size of the alkali metal increases down the group $(K^+ < Rb^+ < Cs^+)$,the lattice energy of the superoxide increases,leading to greater stability.
Therefore,the correct order of stability is: $CsO_2 > RbO_2 > KO_2$.

(B) The reaction $M^{+}_{(g)} \xrightarrow{\text{aqueous medium}} M^{+}_{(aq)}$ represents the hydration of an ion.
Due to the smallest size of the $Li^{+}$ ion among the alkali metals,it has the highest charge density.
This results in the highest hydration enthalpy for $Li^{+}$,making the hydrated $Li^{+}_{(aq)}$ ion the most stable.
Therefore,$Li$ has the highest tendency to undergo this reaction.

(C) The electrolysis of molten $MgCl_2$ is used to extract magnesium.
$NaCl$ and $CaCl_2$ are added to the mixture to lower the melting point of $MgCl_2$ and to increase the electrical conductivity of the electrolyte.
Calcium chloride does not act as a reducing agent in this process.
Therefore,Statement $A$ is true,but Reason $R$ is false.

(A) $CsCl$ is not hygroscopic in nature.
$MgCl_2$,$CaCl_2$,and $LiCl$ are hygroscopic in nature because they have high charge density and small size of cations,which allows them to absorb moisture from the atmosphere.

(B) The electronic configuration $1s^2 2s^2 2p^6 3s^1$ corresponds to Sodium $(Na)$,which is an alkali metal with a valency of $+1$.
Oxygen has an electronic configuration of $1s^2 2s^2 2p^4$ and requires $2$ electrons to complete its octet,thus having a valency of $-2$.
To form a neutral oxide,two metal atoms $(M^+)$ combine with one oxygen atom $(O^{2-})$.
Therefore,the formula of the oxide is $M_2O$.

(C) The reaction between zinc and sodium hydroxide is as follows:
$Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2$
Here,$Na_2ZnO_2$ is sodium zincate.

(D) An amalgam is an alloy of mercury with other metals. $Amalgams$ are widely used in dentistry for filling dental cavities because they are durable,easy to apply,and harden quickly.