Alkali metals Questions in English

(C) The correct matches are:
$1$. Lithium is found in the ore Spodumene $(LiAlSi_2O_6)$.
$2$. Sodium is found in the ore Carnallite $(KCl \cdot MgCl_2 \cdot 6H_2O)$.
$3$. Beryllium is found in the ore Beryl $(Be_3Al_2Si_6O_{18})$.
$4$. Calcium is found in the ore Gypsum $(CaSO_4 \cdot 2H_2O)$.
Therefore, the correct sequence is $1-b, 2-d, 3-a, 4-c$.

(N/A) The oxygen present in water reacts with aluminium to form a thin layer of aluminium oxide $(Al_2O_3)$.
This layer acts as a protective coating,but when water is stored in an aluminium vessel for a long time,some amount of aluminium oxide may dissolve in the water.
Since aluminium ions are toxic and harmful to health,water should not be stored in aluminium vessels overnight.
The reaction is: $2Al(s) + 3H_2O(l) \rightarrow Al_2O_3(s) + 3H_2(g)$.

(N/A) $Ag$,$Cu$,and $Al$ are among the best conductors of electricity. $Ag$ is an expensive metal and $Ag$ wires are very costly. $Cu$ is quite expensive and is also very heavy. $Al$ is a very ductile metal and is lightweight. Thus,$Al$ is used in making wires for electrical transmission.

(A) Chile saltpeter is a naturally occurring mineral deposit found in the Atacama Desert of Chile. Its chemical name is sodium nitrate,and its chemical formula is $NaNO_3$.

(A) Indian saltpeter is the common name for potassium nitrate,which has the chemical formula $KNO_3$.
Chile saltpeter is the common name for sodium nitrate,which has the chemical formula $NaNO_3$.

(A) Cesium $(Cs)$ is widely used in photoelectric cells because it has the lowest ionization energy among the alkali metals,making it highly photosensitive to visible light.

(N/A) Alkali metals with low ionization potential are used in photoelectric cells. For example,$Cs$ (Cesium).

(N/A) Hydrated zeolites are used as ion exchangers in the softening of "hard" water. They exchange their sodium ions $(Na^+)$ with calcium $(Ca^{2+})$ and magnesium $(Mg^{2+})$ ions present in hard water,thereby removing the hardness.

(A) The correct matches are as follows:
$1$. Barium is found in the ore Witherite $(BaCO_3)$.
$2$. Magnesium is found in the ore Carnallite $(KCl \cdot MgCl_2 \cdot 6H_2O)$.
$3$. Potassium is found in the ore Sylvine $(KCl)$.
$4$. Strontium is found in the ore Celestine $(SrSO_4)$.
Therefore,the correct sequence is $1-d, 2-a, 3-b, 4-c$.

(B) The flame colors for alkali metals are as follows:
$1$. $Li$ (Lithium) imparts a crimson red color to the flame.
$2$. $K$ (Potassium) imparts a violet color to the flame.
$3$. $Rb$ (Rubidium) imparts a red-violet color to the flame.
$4$. $Cs$ (Cesium) imparts a blue color to the flame.
Therefore,the correct matching is: $1-a, 2-b, 3-c, 4-d$.

(C) The correct matches are:
$1$. $CaCO_3$ is used as an antacid $(c)$.
$2$. $NaOH$ is used in the preparation of soaps from oils and fats $(a)$.
$3$. $Ca(OH)_2$ is used for making bleaching powder $(d)$.
$4$. $NaHCO_3$ is used as a mild antiseptic in skin infections and as an antacid $(b)$.
Therefore,the correct sequence is $1-c, 2-a, 3-d, 4-b$.

(C) The correct matches are:
$1$. Sodium $(Na)$ is found in Chile saltpetre $(NaNO_3)$.
$2$. Potassium $(K)$ is found in Carnallite $(KCl \cdot MgCl_2 \cdot 6H_2O)$.
$3$. Barium $(Ba)$ is found in Barite $(BaSO_4)$.
$4$. Beryllium $(Be)$ is found in Beryl $(Be_3Al_2Si_6O_{18})$.
Therefore, the correct sequence is $1-d, 2-b, 3-a, 4-c$.

(B) The flame colors of alkali metals are as follows:
$1$. $Li$ (Lithium) imparts a crimson red color to the flame.
$2$. $Na$ (Sodium) imparts a yellow color to the flame.
$3$. $Rb$ (Rubidium) imparts a red-violet color to the flame.
$4$. $Cs$ (Caesium) imparts a blue color to the flame.
Therefore,the correct matching is: $1-d, 2-a, 3-b, 4-c$.
The correct option is $(B)$.

(B) The alloy of lithium and lead,also known as white metal,is primarily used in the manufacturing of engine bearings.

(N/A) $1$. $KOH$ is used in the manufacture of soft soaps.
$2$. It is used as an excellent absorbent of $CO_2$ gas.

(C) The anomalous behavior of lithium is due to the following reasons:
$(i)$ Exceptionally small size of its atom and ion.
$(ii)$ High polarising power (i.e.,charge/radius ratio).
$(iii)$ High ionization enthalpy and lack of $d$-orbitals in its valence shell.

(N/A) The industrially important compounds of $Sodium$ are:
$1$. $Sodium \ carbonate$ $(Na_2CO_3)$
$2$. $Sodium \ hydroxide$ $(NaOH)$
$3$. $Sodium \ chloride$ $(NaCl)$
$4$. $Sodium \ bicarbonate$ $(NaHCO_3)$

(A) The Solvay process is used for the production of sodium carbonate $(Na_2CO_3)$.
It cannot be used for the production of potassium carbonate $(K_2CO_3)$ because potassium hydrogen carbonate $(KHCO_3)$ is highly soluble in water.
In the Solvay process,sodium hydrogen carbonate $(NaHCO_3)$ precipitates out because it is sparingly soluble,but $KHCO_3$ remains in the solution,preventing its isolation by this method.

(C) On heating,the decahydrate $(Na_2CO_3 \cdot 10H_2O)$ loses its water of crystallization to form monohydrate $(Na_2CO_3 \cdot H_2O)$.
Above $373 \ K$,the monohydrate becomes completely anhydrous $(Na_2CO_3)$ and changes to a white powder called soda ash.

(N/A) $(i)$ For softening of hard water.
$(ii)$ In paper,soap,glass,and textile industries.

(C) Impure sodium chloride $(NaCl)$ obtained by crystallization of brine solution contains impurities such as sodium sulphate $(Na_2SO_4)$,calcium sulphate $(CaSO_4)$,calcium chloride $(CaCl_2)$,and magnesium chloride $(MgCl_2)$.

(N/A) $(i)$ It is used as a common salt or table salt for domestic purposes.
$(ii)$ It is used as a raw material for the preparation of $Na_2O_2$,$NaOH$,and $Na_2CO_3$.

(A) Sodium hydroxide $(NaOH)$ is produced on an industrial scale by the electrolysis of brine (aqueous $NaCl$ solution) in the Castner-Kellner cell.
In this process,$Na^+$ ions are discharged at the mercury cathode to form sodium amalgam,which then reacts with water to produce $NaOH$.

(N/A) Sodium amalgam is an alloy or mixture of sodium metal with mercury,represented as $Na-Hg$.
How to obtain sodium amalgam:
It is obtained by the electrolysis of a brine solution ($NaCl$ solution) using a mercury cathode and a carbon anode.
During the process,sodium ions $(Na^+)$ are reduced at the mercury cathode to form sodium metal,which then dissolves in the mercury to form sodium amalgam $(Na-Hg)$.

(N/A) $(i)$ In the purification of bauxite.
(ii) In the textile industries for mercerizing cotton fabrics.

(D) $i$. It is used as a mild antiseptic for skin infections.
$ii$. It is used in fire extinguishers.
$iii$. It is used as an antacid in medicine to neutralize excess stomach acid.

(N/A) $Na^+$ ions are found primarily on the outside of cells,being located in blood plasma and in the interstitial fluid which surrounds the cells. These ions participate in the transmission of nerve signals,in regulating the flow of water across cell membranes,and in the transport of sugars and amino acids into cells.

(N/A) $(1)$ Francium
$(2)$ $21 \ \text{minutes}$
$(3)$ $Li^{+}$
$(4)$ Flame

(A) The element is $Sodium$ $(Na)$.
$Na^{+}$ ions participate in the transmission of nerve signals and the transport of sugars and amino acids into cells.
The formation of its peroxide is as follows:
$2Na + O_{2} \xrightarrow{\Delta} Na_{2}O_{2}$
Reason for flame colour:
The ionisation enthalpy of $Sodium$ is low. When $Sodium$ metal or its salt is heated in a Bunsen flame,the flame energy causes the excitation of the outermost electron to a higher energy level. When this electron reverts to its initial ground state,it releases the absorbed energy as visible light. The emitted radiation corresponds to the yellow region of the spectrum,which is why $Sodium$ imparts a yellow colour to the flame.

(N/A) $(1)$ $Li_3N$
$(2)$ Violet
$(3)$ Cesium,potassium
$(4)$ Ammoniated electrons

(N/A) $(1)$ Armour plates.
$(2)$ Yellow or orange.
$(3)$ Lithium monoxide $(Li_{2}O)$ and lithium nitride $(Li_{3}N)$.
$(4)$ Lithium oxide $(Li_{2}O)$.

(N/A) $(1)$ The Solvay process is used to prepare sodium carbonate.
$(2)$ Sodium carbonate exists as decahydrate,$(Na_2CO_3 \cdot 10H_2O)$,commonly known as washing soda.
$(3)$ Sodium chloride is commonly known as common salt or table salt.
$(4)$ Sodium chloride melts at $1081 \ K$.

(A) $(1)$ Caustic soda
$(2)$ Sodium hydroxide,dihydrogen $(H_2)$ gas
$(3)$ Sodium carbonate $(Na_2CO_3)$
$(4)$ Baking soda

(A) $(1)$ False statement: The half-life of $^{223}Fr$ is $21 \ min$.
$(2)$ True statement: $Li^{+}$ has a small size and high charge density,leading to high hydration enthalpy,which makes its salts hydrated.
$(3)$ False statement: Only $Li$ reacts directly with nitrogen of air to form the nitride $Li_3N$.
$(4)$ False statement: $LiF$ is insoluble in water due to its high lattice enthalpy,while other $Li$ halides are soluble in water and organic solvents like ethanol,acetone,and pyridine.

(N/A) Alkali metals react with $O_{2}$ and their reactivity increases down the group. These elements form three types of oxides: normal oxides,peroxides,and superoxides.
$1. \ Li$ forms mainly the normal oxide: $4 Li + O_{2} \xrightarrow{\Delta} 2 Li_{2}O$
$2. \ Na$ forms mainly the peroxide: $2 Na + O_{2} \xrightarrow{\Delta} Na_{2}O_{2}$
$3. \ K$ forms mainly the superoxide: $K + O_{2} \xrightarrow{\Delta} KO_{2}$
Superoxide $(O_{2}^{-})$ is stable only with large-sized cations like $K^{+}$,$Rb^{+}$,and $Cs^{+}$.

(N/A) The resemblance between $Li$ and $Mg$ is due to the diagonal relationship in the periodic table, which arises from their similar ionic radii and charge-to-size ratios (ionic potential).
$1$. Both $Li$ and $Mg$ react slowly with water. Their oxides and hydroxides are much less soluble in water compared to other alkali and alkaline earth metals, and their hydroxides decompose on heating.
$2$. Both elements form nitrides by direct combination with nitrogen, i.e., $Li_3N$ and $Mg_3N_2$.
Reason: This similarity is primarily due to their comparable ionic radii ($Li^+ = 76 \text{ pm}$ and $Mg^{2+} = 72 \text{ pm}$) and similar electronegativity values, which lead to similar polarizing power.

(N/A) The $Li^+$ ion has the smallest size among alkali metal ions and possesses high polarizing power,which imparts significant covalent character to its compounds according to Fajan's rule. Due to this covalent nature,lithium compounds are more soluble in organic solvents. In contrast,other alkali metal compounds are predominantly ionic and are therefore highly soluble in water.

(N/A) The reaction between $(NH_4)_2CO_3$ and $NaCl$ would theoretically produce $Na_2CO_3$ and $NH_4Cl$.
However,both $Na_2CO_3$ and $NH_4Cl$ are highly soluble in water.
Because the products remain in the ionic form in the solution,the equilibrium does not shift in the forward direction to precipitate $Na_2CO_3$.
Therefore,$Na_2CO_3$ cannot be prepared directly by this method.

(A-6, B-4, C-2, D-3, E-5, F-1) The correct matches are: $A-6, B-4, C-2, D-3, E-5, F-1$.
This occurs because the heat from the flame excites the outermost orbital electron to a higher energy level.
When the excited electron returns to the ground state,it emits radiation in the visible region,imparting a characteristic colour to the Bunsen flame.

(A) The atoms of alkali metals have a large size,and due to this,they readily form cations,making their compounds ionic in nature. Alkali metals exhibit a $+1$ oxidation state and form ionic compounds.
Alkali metals form three types of oxides: Normal oxides $(M_{2}O)$,Peroxides $(M_{2}O_{2})$,and Superoxides $(MO_{2})$.
The basic character of normal oxides increases from $Li_{2}O$ to $Cs_{2}O$ due to an increase in their ionic character.
Halides of alkali metals $(MX)$ are generally ionic,except for $LiX$,which is covalent due to the small size and high polarizing power of the $Li^{+}$ ion.
Oxosalts: All alkali metals form solid carbonates with the general formula $M_{2}CO_{3}$. These carbonates are stable,except for $Li_{2}CO_{3}$,which is unstable and decomposes due to the high polarizing capacity of $Li^{+}$. All alkali metals (except $Li$) form solid bicarbonates $(MHCO_{3})$. All alkali metals form nitrates with the formula $MNO_{3}$,which are colourless,water-soluble,electrovalent compounds.

(N/A) Alkali metals dissolve in liquid ammonia to form a blue solution due to the presence of ammoniated electrons. These electrons absorb energy in the visible region of light and impart a blue colour to the solution.
$M + (x+y) NH_{3} \rightarrow [M(NH_{3})_{x}]^{+} + [e(NH_{3})_{y}]^{-}$
$(b)$ In a concentrated solution,the blue colour changes to bronze colour due to the formation of metal ion clusters. On standing,the blue solution liberates $H_{2}$ gas and forms a metal amide.
$M^{+} + e^{-} + NH_{3} \rightarrow MNH_{2} + \frac{1}{2} H_{2}$
The product formed is a metal amide.

(N/A) The stability of peroxides and superoxides increases as the size of the alkali metal cation increases down the group.
This is because larger cations are more effective at stabilizing the large,highly polarizable peroxide $(O_{2}^{2-})$ and superoxide $(O_{2}^{-})$ anions through lattice energy effects.
As the size of the metal cation increases from $Li^{+}$ to $Cs^{+}$,the lattice energy of the resulting ionic compounds becomes more favorable for these larger anions.
For example,the stability order for superoxides is $KO_{2} < RbO_{2} < CsO_{2}$.

(N/A) The reducing power of an element is determined by the standard electrode potential $(E^{\circ})$,which depends on three factors: sublimation enthalpy,ionization enthalpy,and hydration enthalpy.
$Li(s) \rightarrow Li(g)$ (Sublimation enthalpy)
$Li(g) \rightarrow Li^{+}(g) + e^{-}$ (Ionization enthalpy)
$Li^{+}(g) + H_2O \rightarrow Li^{+}(aq)$ (Hydration enthalpy)
Although $Li$ has the highest ionization enthalpy among alkali metals,it has the smallest size,which results in the highest hydration enthalpy. This large negative hydration enthalpy compensates for the high ionization enthalpy,making the overall process highly favorable. Consequently,$Li$ has the most negative standard electrode potential $(E^{\circ} = -3.04 \ V)$,making it the strongest reducing agent in aqueous solution.

(N/A) All alkali metals have a common outer electronic configuration of $ns^1$,where $n$ represents the principal quantum number. This uniform electronic configuration is the primary reason for their similar chemical properties and their placement in Group $1$ of the periodic table. The electronic configurations are as follows:

Element	Electronic Configuration
$Li$ $(Z=3)$	$[He] 2s^1$
$Na$ $(Z=11)$	$[Ne] 3s^1$
$K$ $(Z=19)$	$[Ar] 4s^1$
$Rb$ $(Z=37)$	$[Kr] 5s^1$
$Cs$ $(Z=55)$	$[Xe] 6s^1$
$Fr$ $(Z=87)$	$[Rn] 7s^1$

(D) The given elements $(Li, Na, K, Rb)$ belong to Group $1$ (Alkali metals).
Metallic character increases down the group as the ionization enthalpy decreases and the atomic size increases.
Therefore,$Rb$ has the highest metallic character among the given elements.

(B) Mercury $(Hg)$ is the only metal that exists in a liquid state at room temperature.

(N/A) Alkali metals are highly reactive because they have the lowest ionization enthalpy values in their respective periods,allowing them to easily lose their valence electron to form $M^+$ ions.

(N/A) The alkali metal hydride that exhibits significant covalent character and is relatively unreactive towards oxygen and chlorine is lithium hydride,$LiH$.
It is used in the synthesis of other useful hydrides like $LiAlH_4$.
The reaction of $LiH$ with $Al_2Cl_6$ is:
$8LiH + Al_2Cl_6 \rightarrow 2LiAlH_4 + 6LiCl$.

(B) Both $Li$ and $Mg$ exhibit diagonal relationship and show similar chemical properties.
$Li$ and $Mg$ do not form solid hydrogencarbonates ($LiHCO_3$ and $Mg(HCO_3)_2$ are unstable in solid state).
Both $Li$ and $Mg$ react directly with nitrogen to form their respective nitrides,$Li_3N$ and $Mg_3N_2$.

(D) $Cs$ (Cesium) is used in photoelectric cells because it has the lowest ionization energy among all stable elements,allowing it to emit electrons easily when exposed to light.