s-block ELEMENTS NEETIIT.COM Alkali metal (a) All are light metals (b) Density increases gradually from Li to Cs.

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1 NEETIITCM s-blck ELEMENTS 1 INTRDUCTIN (a) Elements of group 1 (or I A) and 2 (or II A) are known as s-block elements (b) Their (n 1) shells are completely filled and differentiating (last) electron enters into ns sub-orbit (c) General electronic configurations are Group 1 [Inert gas]ns 1 Alkali metals Group 2 [Inert gas] ns 2 Alkaline Earth metals 2 THE ALKALI METALS (a) Group 1 elements are called as alkali metals because their oxides and hydroxides when treated with water, form alkaline solutions (b) This includes the typical or representative elements such as Li and Na as well as K, Rb, Cs and Fr (c) Because of their high reactivity, they are never found in the free state 4 PHYSICAL PRPERT IES F s-blck ELEMENTS Property 41 Density 42 Mpt and Bpt l (d) Because of similarity in electronic configuration, they exhibit similar properties (e) A regular gradation in their properties with increase in atomic number is observed due to increasing size of atoms / ions (f) f all the alkali metals, only sodium and potassium are found in abundance in nature (g) Francium occurs only in minute quantities as a radioactive decay product and due to its radioactiv e nature it possesses some remarkable difference, it is not included in following studies 3 THE ALKALINE EARTH METALS (a) Group 2 elements are called alkaline earth metals because their alkaline oxides are nonfusible like earth matter Si 2, and were known before the discovery of these elements and thus are called alkaline earth metals (b) This includes the typical elements Be and Mg as well as Ca, Sr, Ba and Ra NEETIITCM 43 specific heat Alkali metal (a) All are light metals (b) Density increases gradually from Li to Cs (c) Li is lightest known metal among all (d) K is lighter than Na because of low density (a) The lattice energy of these atoms in metallic crystal lattice is relatively low and thus these possess low m pt & b pt (b) Lattice energy decreases from Li to Cs and thus m pt and b pt also decrease from Li to Cs It decreases from Li to Cs Li > Na > K > Rb > Cs Alkaline earth metal (a) Heavier than alkali metals (b) Density decrease slightly up to Ca after which it increases (c) Density of Mg is greater than Ca (a) Melting points and boiling points are more than that of alkali metals (b) Do not show any regular trend The trend is not regular however values are greater than that of alkali metals 44 Physical state (a) All are silvery white metals (b) Light soft, malleable and ductile metals with metallic lustre (c) Both are diamagnetic and colourless in form of ions (a) All are greyish white (b) Relatively harder NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 1

2 NEETIITCM Property 45 Conducting power Alkali metal Both are good conductor of heat and electricity Alkaline earth metal 46 Flame colour 47 Ionisation Energy 48 Hydration of ions NEETIITCM 49 xidation no and valency (a) Both produces characteristic colour in bunsen flame due to easy excitation of electron to higher energy levels (b) Characteristic flame colours are Li Crimson, Na Golden Yellow, K Pale violet, Rb and Cs Violet (c) Energy released Li + < Na + < K + < Rb + < Cs + (d) The flame energy causes an excitation of the outermost electron which on reverting back to its initial position gives out the absorbed energy as visible light (a) Due to unpaired electrons in ns sub shell as well as due to their larger size, the outermost electron is far from the nucleus, the removal of electron is easier and these have low values of ionisation potential (b) IP of these metals decreases from Li to Cs (a) Hydration represents for the dissolution of a substance in water to get absorb water molecule by weak valency forces Hydration of ions in the process when ions on dissolution in water get hydrated (b) Smaller the cation greater is the degree of hydration Hydration energy - Li + > Na + > K + > Rb + > Cs + (c) Li + being smallest in size has maximum degree of hydration and that is why lithium salts are mostly hydrated and moves very slowly under the influence of electric field (a) These elements easily form univalent +ve ion by losing solitary ns 1 electrone due to low IP value (a) Be and Mg do not show any colour as their electrons are more strongly bound (b) Ca Brick red, Sr Crimson Ba apple green, Ra Crimson (c) Be and Mg atoms due to their small size, bind their electrons more strongly because of higher effective nuclear charge Hence these posses high excitation energy and are not excited by the flame energy and do not show any colour (a) Due to smaller size, electrons are tightly held as compared to alkali metal (b) The IP, values decreases with increase of atomic radii from Be to Ba (b) Hydration energy - Be +2 > Mg +2 > Ca +2 > Sr +2 > Ba +2 (a) The IP 1 of these metals are much lower than I P 2 and thus it appears that these metals should form univalent ion rather than divalent ions but in actual practice, all these give bivalent ion NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 2

3 NEETIITCM Property Alkali metal Alkaline earth metal 410 Electronegativity (a) These metals are highly electopositive and thereby possess low values of electro negativities (b) Electronegativity of alkali metals decreases down the group Li > Na > K > Rb > Cs (a) Their electronegativities are also small but are higher than that of alkali metals (b) Electronegativty decrease from Be to Ba 411 Standard oxidation potential and reducing properties Examples based on (a) Since alkali metals easily lose ns 1 electron, they have high values of oxidation potential ie M + aq M? aq + e - (b) Standard oxidation potentials are listed below Li Na K Rb Cs (c) Li have greatest reducing nature due to maximum hydration energy of Li + ion Physical properties of s-block Element Ex1 The density of - (A) Na > K (B) Na = K (C) K > Na (D) Li > K Ans [A] Sol The densities of elements of group 1are quite low (Li = 0534 g/cc, Na = 0972, K = 0559, Rb = 153, Cs = 1903) It increases gradually in moving from Li to Cs However potassium is lighter than sodium probably due to an unusual increase in atomic size of potassium Ex2 Alkali metals ions sare - (A) Diamagnetic and coloured (B) Diamagnetic and colourless (C) Paramagnetic and coloured (D) Paramagnetic and colourless Ans [B] Sol Since the electronic configurations of M + ions are similar to those of noble gases (s 2 or s 2 p 6 ), these ions have no unpaired electrons and consequently are diamagnetic and colourless (a) They lose two electrons to give M +2 ion (b) Std oxidation potential are Be Mg Ca Sr NEETIITCM Ex3 Alkali metals show - (A) nly + 1 oxidation state (B) nly 1 oxidation state (C) + 1 and + 2 oxidation states (D) 1 and 2 oxidation states Ans [A] Sol Due to their low ionisation energies, these elements can easily form the univalent ions (M + ions) by losing the single ns 1 electron Since the unipositive ions have the stable noble gas configuration (s 2 or s 2 p 6 ) in the valence shell, the energy required to pull out another electron from the valence shell is very high ie the second ionisation energies of these metals are very high Therefore, under ordinary conditions, it is not possible for the metals to form M 2+ ions Therefore, they show only + 1 oxidation state Ex4 The correct order of decreasing hydrated radius - (A) Na + (aq) > Li + (aq) > K + (aq) > Rb + (aq) > Sol Cs + (aq) (B) K + (aq) > Li + (aq) > Na + (aq) > Rb + (aq) > Cs + (aq) (C) Cs + (aq) > Rb + (aq) > K + (aq) > Na + (aq) > Li + (aq) (D) Li + (aq) > Na + (aq) > K + (aq) > Rb + (aq) > Cs + (aq) Ans [D] Hydration energy and hydrated radius decrease down the group with increase in the size of cation Li? aq > Na? aq > K? aq > Rb?? aq > Cs aq NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 3

4 NEETIITCM Ex5 Which of the following does not colour the flame - (A) Li and Be (B) Li and Na (C) Be and Mg (D) Li and Mg Ans [C] 5CHEMICAL PRPERTIES F s-blck ELEMENTS Sol Be & Mg has a high value of IE Energy of flame is not sufficient to excite their electron Property Alkali metal Alkaline earth metal 51 Action with air 52 Action with water 53 Hydrides (a) n exposure to moist air, all alkali metals except lithium tarnish quickly (b) The effect of atmosphere increases from Li to Cs, that is why these are kept in kerosene oil (c) They generally form oxides and peroxides M+ 2??? M 2 2 M 2 2 xide Peroxide (a) Alkali metals decompose water with the evolution of hydrogen 2M+2H 2 2MH (b) Li decompose water slowly, sodium reacts with water quickly K, Rb & Cs react with water vigorously (c) Alkali metals react with alcohols forming alkoxides with the evolution of hydrogen 2Li+2C 2 H 5 H? 2C 2 H 5 Li Ethyl alcohol Lithium ethoxide (a) These metals combine with H to give white crystalline ionic hydrides of the general formula MH (b) The tendency to form their hydrides decreases from Li to Cs, since the electropositive character decreases from NEETIITCM Cs to Li 2M 2MH (c) The metal hydrides react with water to give MH & H 2 MH MH (a) Except beryllium these metals are easily tarnish in air as a layer of oxide is formed on their surface (b) The effect of atmosphere increases as the atomic number increases (c) They give oxides of ionic nature M +2-2 which are crystalline in nature (a) Ca, Sr, Ba and Ra decompose cold water readily with evolution of hydrogen M+2 H 2 M (H (b) Magnesium decomposes boiling water but beryllium is not attacked by water even at high temperatures as its oxidation potential is lower than the other members (a) Except Be, all alkaline earth metals form hydrides (MH 2 ) on heating directly with H 2 (b) The stability of hydrides decreases from Be to Ra (c) BeH 2 is prepared by the action of LiAlH 4 on BeCl 2 BeCl 2 +LiAlH 4? 2BeH 2 +LiCl+ AlCl 3 BeH 2 & MgH 2 is covalent but other are ionic (d) The ionic hydrides of Ca, Sr, Ba liberate H 2 at anode and metal at cathode NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 4

5 NEETIITCM Property Alkali metal Alkaline earth metal 54 Carbonates and bicarbonates 55 Halides (a) The carbonates (M 2 ) & bicarbonates (MH ) are highly stable to heat, where M stands for alkali metals (b) The stability of these salts increases with the increasing electropositive character from Li to Cs It is therefore Li 2 decompose on heating Li 2 Li 2 + C 2 (c) Bicarbonates are decomposed at relatively low temperature 2MH 3000 C M 2 +H 2 + C 2 (d) Hydrolysis of carbonate + 2H 2? 2NaH Li 2 sparingly soluable (a) Alkali metals combine direct with halogens to form ionic halide MX (b) The case with which the alkali metals form halides increases form Li to Cs due to increase in electropositive character (c) LiX have more covalent character (d) Halides having ionic nature have high m pt and are good conductor of current in fused state These are readily soluble in water NEETIITCM (e) Halides of potassium, rubidium and ceasium have property of combining with extra halogen atoms forming polyhalides KI + I 2 KI 3 (a) All these metal carbonates M are insoluble in neutral medium but soluble in acids and decompose on red heating (b) The stability of carbonates increases with increase in electropositive character of metal (c) Bicarbonates of alkaline earth metals do not exist in solid state but are known in solution only on heating their solution bicarbonates decomposed to liberate C 2 M(H M +C 2 +H 2 (Solution) (d) Solubility of carbonates decrease on moving down the group (a) The alkaline earth metals directly combine with halogens on heating to give metal halides MX 2 (b) The ionic character of halides increases from Be to Ra (c) Beryllium halides have covalent character due to small size and high effective nuclear charge and thus do not conduct electricity in molten state (d) The solubility of halides in water decreases down the group Except fluorides, all are fairly soluble in water (e) The decreases in solubility of halides down the group is due to decrease in hydration energy because of increasing size of metal cation (f) The halides are hygroscopic and readily form hydrates CaCl 2 6H 2, BaCl 2 2H 2 (g) CaCl 2 has strong affinity with water and is used as dehydrating agent NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 5

6 NEETIITCM Property Alkali metal Alkaline earth metal 56 Sulphates 57 Nitrates 58 Solubilities in Liq NH 3 NEETIITCM 59 Complex ion formation (a) All these form sulphates of type M 2 S 4 (b) Except Li 2 S 4 rest all are soluble in water (c) These sulphates on fusing with carbon form sulphides M 2 S 4 + 4C? M 2 S + 4C (a) Nitrates of both are soluble in water and decompose on heating (b) LiN 3 decomposes to give N 2 and 2 and rest all give nitrites and oxygen 2MN 3? 2MN (except Li) 4LiN 3? 2Li 2 + LiN (a) Both metals dissolve in liquid NH 3 to produce coloured solution which conducts electricity to an appreciable degree (b) With increasing concentration of metal in ammonia the blue colour starts changing to that of metallic copper after which dissolution of alkali metals in NH 3 ceases (c) The metal atom is converted into ion and the electron set free combined with NH 3 molecule to produce blue ammonia solvated electron Na Na + (in Liq NH 3 ) + e? (Ammoniated) M+( x + y) NH 3 [ M( NH 3 ) x ] + + e? (NH 3 ) y (solvated electron) (d) It is the ammoniated or ammonia solv ated electron which is responsible for conducting power, blue colour, paramagnetic nature and reducing power of alkali metals in ammonia solution (e) The stability of metal - ammonia solution decreases form Li to Cs (a) A metal shows complex formation only when it has f ollowing characteristics Small size (ii) High nuclear charge (iii) Presence of empty orbitals in order to accept electron pair from ligand (a) MS 4 type sulphates are formed (b) The solubility of sulphates decreases on moving down the group BeS 4 is soluble in water while BaS 4 is completely insoluble (c) MS 4 + 2C? MS + C 2 (b) n heating they decompose into their corresponding oxides with evolution of a mixture of nitrogen dioxide and oxygen M(N 3? M+2Ns 2 +½ 2 When such a solution is evaporated, hexammoniate, M(NH 3 ) 6 is formed NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 6

7 NEETIITCM Property Alkali metal Alkaline earth metal 510 Formation of amalgams 511 Basic nature of hydroxide 512 Reaction with acids 513 Extraction Examples based on (b) nly Lithium in alkali metals due to small size, forms a few complex ions Rest all alkali metals do not possess the tendency to form complex ion (a) Alkali metals and alkaline earth metals get dissolved in mercury to form amalgams with evolution of heat and the amalgamation is highly exothermic (b) Alkali metals form alloys themselves as well as with other metals (a)? 2NaH? 2Na + + H The order is LiH < NaH < KH < RbH < CsH (a) Reacts vigorously with acids 2M S 4? M 2 S 4 (a) Alkali metals being strong reductant, cannot be extracted by reduction of their oxides and other compounds (b) n account of strong electropositive character, it is not possible to use the method of displacing them from their solutions by any other element (c) Electrolysis of their aqueous solution cannot be applied as hydrogen is liberated at cathode in place of alkali metals as their discharge potential is very high (b) Be +2 on account of smaller size forms many complexes such as [Be F 3 ] -1, [BeF 4 ] -2 (a) The order is Be(H <Mg(H < Ca(H < Sr(H < Ba(H (a) Freely reacts with acids and displaces hydrogen M + 2HCl? MCl 2 (a) Alkaline earth metals being reducing agents cannot be extracted by ordinary chemical reduction methods (b) Electrolysis of aqueous solution of their compounds cannot be employed for extraction as they react with water (c) The metals are best extracted by the electrolysis of their fused metal halides containing NaCl Addition of NaCl reduces the fussion temperature NEETIITCM Chemical Properties of s-block Elements Ex6 Basic character is maximum for - (A) LiH (B) CsH (C) KH (D) NaH Ans [B] Sol Basic charater of hydroxides increase down the group Ex7 Sol Which of the following halides has the highest melting point - (A) NaCl (B) NaI (C) NaBr (D) NaF Ans [D] Lattice energy increase in following order MI < MBr < MCl < MF (M = Metal) Ex8 Which of the following does not give an oxide on heating - (A) Mg (B) Li 2 (C) Zn (D) K 2 Ans [D] Sol Alkali metal carbonates (except Li 2 ) do not decompose on heating Ex9 When heated in steam, Mg burns brilliantly producing - (A) Mg(H (B) Mg and H 2 (C) Mg and 2 (D) Mg and 3 Ans [B] Sol Mg Mg NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 7

8 NEETIITCM Ex10 A blue coloured solution of sodium in liquid NH 3 acts as strong reducing agent, because - (A) of ammoniated sodium (B) ammonia dissociates (C) sodium nitride is formed (D) of ammoniated electron Ans [D] Sol Na + (x + Y) NH 3 Na + (NH 3 ) x + e - (NH 3 ) y Ex11 Sol When magnesium ribbon is heated to redness in an atmosphere of nitrogen and subsequently cooled with water, the gas evolved is - (A) N 2 (B) NH 3 (C) N 2 (D) C 2 Ans [B] Magnesium reacts with nitrogen to form magnesium nitride, Mg 3 N 2 as a greenish yellow amorphous powder It reacts with water forming magnesium hydroxide and ammonia Mg 3 N 2 + 6H 2 3Mg(H + 2NH 3 6 EXCEPTINAL PRPERTIES SHWN BY s-blck ELEMENTS In s-block elements Li & B e shows anomalous behavior due to their extremely small size 61 Anomalous behavior of Lithium (a) The first member of alkali group exhibits the characteristic properties but it differs at time in many respects from them due to small atomic and ionic size (b) n account of its small size exerts the greatest polarising effect out of all the alkali metals and ions,consequently covalent character is developed (c) Li has the highest ionisation energy and electronegativity as compared to other alkali metals (d) It is not affected by air easily and does not lose its lustre even on melting (e) It is more harder and lighter than other alkali metals (f) It reacts slowly with water to liberate hydrogen (g) It does not react with oxygen below 0 o C When burnt in air or oxygen, it forms only monoxide, Li 2 However, the rest of the alkali metals give peroxide or superoxides (h) Li 2 is much less basic than oxides of other alkali metals Lithium is the only alkali metal which directly reacts with nitrogen to from Li 3 N 6Li + N 2 2Li 3 N (j) Lithium hydroxide decomposes at red heat to form Li 2 Hydroxides of other alkali metals do not decompose 2 LiH Li 2 (k) LiH is known in solution but not in solid state while the bicarbonates of other alkali metals are known in solid state (l) Li 2 is less stable, as it decomposes on heating Li 2 Li 2 + C 2 (m) Li 2 S 4 is the only alkali metal sulphate, which does not form double salts eg, alum (n) Lithium reacts with bromine very slowly ther alkali metal react violently (o) Li when heated in NH 3 forms imide Li 2 NH while other alkali metals form amides MNH 2 (p) LiH is much weaker base than NaH or KH (q) Lithium shows resemblance with magnesium, an element of group II A This resemblance is termed as diagonal relationship 62 Anomalous behaviour of Beryllium (a) It is the hardest of all alkaline earth metal as maximum metallic bonding is their due to smallest size (b) The melting and boiling points of the beryllium are the highest (c) It is least reactive due to highest ionisation potential (d) due to low value of oxidation potential it does not decompose water (e) Due to high charge density its polarising effect is highest and it forms covalent bond (f) Be does not react directly with hydrogen (BeH 2 is formed by indirect method) NEETIITCM (g) It dissolves in alkalies with evolution of hydrogen Be + 2 NaH + 2 H 2 Be 2 2H 2 Sodium beryllate other alkaline earth metals do not react with alkalies (h) It does not liberate hydrogen from acids readily due to lowest oxidation potential amongst alkaline earth metals xides and hydroxides of beryllium are amphoteric in nature Be S 4 BeS 4 Be + 2 NaH Be 2 NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 8

9 NEETIITCM Be has a 4 : 4 Zinc sulphide (Wurtzite) Structure, but all others have a 6 : 6 sodium chloride structure Be (H + 2HCl BeCl + 2H 2 Be (H + 2HCl Be 2 + 2H 2 The hydroxide is unstable in water and is covalent in nature (j) Like Al, its carbide (Be 2 C) on hydrolysis evolves methane (k) Its carbonate is instable towards heat (l) As very high energy is required to excite electron from lowest energy state (m) Due to its small size it has strong tendency to form complex (n) It shows diagonal relationship with Al Examples based on Ex12 Sol Exceptional Properties Shown by s-block elements Both Be and Al become passive on reaction with conc nitric acid due to (A) The non reactive nature of the metal (B) The non reactive nature of the acid (C) The formation of an inert layer oxide on the surface of the metals (D) None of these Ans [C] Both Be and Al are rendered passive due to formation of inert, insoluble and impervious oxide layer on their surface Ex13 Which of the following is an amphoteric oxide - (A) Ca (B) Sr (C) Be (D) Mg Ans [C] Sol Be, because it is least electropositive in its group Therefore, instead of basic oxide, it forms amphoteric oxide Ex14 Sol Ex15 Which one of the following is most stable in ether - (A) BeCl 2 (B) CaCl 2 (C) SrCl 2 (D) None of these Ans [A] Due to smaller cation BeCl 2 is most covalent and is most stable in ether NEETIITCM Li has the maximum value of ionisation potential among alkali metals ie lithium has the minimum tendency to ionise to give Li + ion Thus, lithium is - (A) Strongest reducing agent (B) Poorest reducing agent (C) Strongest oxidising agent (D) Poorest oxidising agent Ans [A] Sol 7 SDIUM The ionisation potential value of Lithium is maximum among alkali metals ie its tendency to ionise to give Li + ions should be the minimum ie Li should be the poorest reducing agent But, lithium is the strongest reducing agent This is due to the largest value of hydration energy of Li + ions 71 ccurence Alkali metals are highly reactive, they do not occur in free state In combined state they are found in the form of ores 72 res of Sodium Rock salt or sodium chloride - NaCl (ii) Chile salt petre or sodium nitrate - NaN 3 (iii) Borax or sodium borate - B H 2 (iv) Glauber's salt - S 4 10H 2 (v) Cryolite - Na 3 AlF 6 (vi) Soda Feldspar - NaAl Si Extraction of Sodium Sodium is extracted from sodium chloride by a process known as Down's process Down's Process : Sodium is obtained by the electrolysis of a mixture of sodium chloride (40%) and calcium chloride (60%) CaCl 2 which is a fusing agent is added to lower the melting point of NaCl from 1085K to 850 K The main reason of lowering the temperature are - (a) The melting point of NaCl is very high and it is very difficult to maintain this temperature (b) Sodium is volatile at high temperature and therefore a part of metal possesed may vapourise forming fog (c) Chlorine produced as by product may corrode the material of the vessel at this temperature (d) The metal obtained at this temeprature will be in collidal state and its seperation will be difficult (ii) By Electrolysis : NaCl Na + + Cl At cathode : Na+ + e Na At anode : Cl Cl + e Cl + Cl Cl 2 NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 9

10 NEETIITCM Note : Aqueous sodium chloride cannot be used for preparing sodium by electrolysis Because instead of metallic sodium, hydrogen gas will be liberated at cathode 74 Properties Highly reactive, so kept in kerosene (ii) Na dissolve in liquid NH 3 Blue solution (iii) It form sodium amalgam with mercury (iv) Action of Air 75 Uses 4Na + 2 Moist???? 2 Air 4NaH C??? 2? + 2H H???? Sodium with lead alloy is used to prepare tetraethyl lead (C 2 H 5 ) 4 Pb, which acts as an antiknock compound for petrol 4C 2 H 5 Cl + 4Na + 4Pb (C 2 H 5 ) 4 Pb + 4NaCl + 3Pb (ii) In sodium v apour lamp, which emits monochromatic yellow light (iii) Used for the preparation of useful reagents such as NaNH 2 (sodamide), 2, NaCN 8 CMPUNDS F SDIUM 81 Sodium Chloride (NaCl) 811 Preparation Sea water is the major source of sodium chloride Sea water Evaporation?????? Crude NaCl By Solar Heat (27 to 29% of NaCl) NEETIITCM It contains impurities of S 4, MgCl 2, CaCl 2 etc (ii) Insoluble impurities removed by filtration HCl gas passed (iii) Filtrate??????? Pure NaCl (ppt) Then HCl gas is passed through the solution to get saturated solution due to common ion effect, the crystals of pure NaCl seperate out (iv) MgCl 2 and CaCl 2 being in the solution (ii) Its solubility in water is 36 gm in 100 gm of water at 0 C (iii) Pure sodium chloride is non-hygroscopic but due to the impurities of CaCl 2 2H 2 and MgCl 2 2H 2 it behave as hygroscopic (iv) Reaction with K 2 Cr 2 7 S 4 (conc) 813 Uses 4NaCl + K 2 Cr H 2 S 4??? 4NaHS 4 S 4 + 2Cr 2 Cl 2 + 3H 2 (range red) Used as a table salt, an essential constituent of our food (ii) It is used in freezing mixture 82 Sodium Carbonate ( ) It exists in various form : Soda ash H 2 : Crystal corbonate 7H 2 : Hepta hydrate 10H 2 : Washing soda 821 Preparation (a) Solvay Process : When C 2 gas is passed through a brine solution (about 28% NaCl) saturated with ammonia, it gives NaH NH 3 + C 2 NH 4 H NH 4 H + NaCl NaH + NH 4 Cl The precipitated sodium bicarbonate is filtered and dired ie Calcination :? 2NaH??? + C 2 Raw material for the process are - Sodium (chloride NaCl) (ii) Limestone (Ca ) for C 2 (iii) Ammonia gas (NH 3 ) Impurities of MgCl 2 and CaCl 2 salts are precipeted as their carbonates (b) Leblanc Process : NaCl S 4 NaHS 4 + NaCl??? NaHS 4 + HCl at high????? temp S 4 + HCl 812 Properties FCC structure of solid S 4 + 4C??? S + 4C S + Ca CaS + NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 10

11 NEETIITCM 822 Properties Hydrolysis : + 2H 2 H 2 + 2NaH (ii) It reacts with metal (MgCl 2, CaCl 2 ) to form insoluble basic carbonate CaCl 2 + Ca + 2NaCl while carbonates of metals like Fe, Al, Sn etc when formed are immediately hydrolysis Fe(S 4 ) + 3 Fe 2 ( ) 3 (iii) Efflorescence : 823 Uses 3H 2???? 2Fe(H) 3 + 3C 2 10H 2 when exposed to air it give nine out of ten H 2 molecules 10H 2 H 2 + 9H 2 This process is called efflorescene For making fusion mixture - + K 2 (II) In textile and petrolieum refining 83 Sodium Bicarbonate or Baking Soda (NaH ) 831 Preparation It is obtained as an intermidate product in solvay's process for the manufacture of 832 Properties Its aqueous solution is alkaline in nature NaH NaH (H 2 + C 2 ) NEETIITCM (ii) It reacts with acids (HCl, H 2 S 4 ) and evolves C 2 NaH + HCl NaCl + C 2 (iii) When equimolar amounts of and NaH are dissolved in water and the resulting solution cooled to 35 C, crystals of sodium sesquicarbonate NaH 2H 2 seperate out It is neither deliquescent nor efflorescence and is used for wool washing 833 Uses In the preparation of baking powder (ii) In the prepartion of effervescent drinks - and fruit salts (iii) In medicines to reince acidity of the stomach (as Antacid) (iv) In the fire extinguishers 84 Sodium Hydroxide (Caustic Soda), NaH 841 Preparation Caustisization process (Gassage Process) : Involves heating of a 10% solution of with a little excess of milk of lime [Ca(H ] + Ca(H Ca + 2NaH (ii) Electrolytic Method : (a) Nelson cell or Diaphragm cell : NaCl(Aq) H 2 H + + H Na + + Cl At Cathode : (Perforated steel) 2H + + 2e H 2 At Anode : (Graphite) 2Cl Cl 2 + 2e Note : Here H + ions of H 2 are not discharged because of the high potential of halogen over mercury Sodium amalgam is removed from the cell It is then decomposed in a seperate cell by water 2Na Hg + 2H 2 2NaH + Hg 842 Properties It absorbs C 2 from air forming (ii) It may be purificd by dissolving it in alcohol in which impurities including are insoluble (iii) Reaction : (a) NaH + S 2 S 3 (b) NaH + Si 2 Si 3 (Sodium silicate or glass) (cnah + Al 2 3 2NaAl 2 (Sodium Aluminate) NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 11

12 NEETIITCM (iv) Reaction with Non metals : 9 CALCIUM (a) No reaction with H 2, N 2 and C (a) Its important ores are : (b) Limestone, (Marble) Ca (ii) Gypsum CaS 4 2H 2 (c) X 2 + 2NaH NaX + NaX cold Sodium Hypohalite 3X 2 + 6NaH NaX + NaX 3 + 2H 2 hot Sodium Halate (v) Reaction with Metals : (a) With Alkali metals : No reaction (b) (c) Formation of unstable hydroxides : HgCl 2 + 2NaH 2NaCl + Hg(H NEETIITCM???? Hg (Yellow) 2AgN 3 + 2NaH 2NaN 3 + 2AgH (Brown) (vi) Action of carbon monooxide : NaH + C (vii) Caustic Property :???? Ag ???? C?? HCNa NaH is a powerful caustic and breaks down proteins of the skin and flesh to a pasty mass, therefore it is commonly known as caustic soda (iii) Dolomite Ca Mg (iv) Fluorspur CaF 2 (v) Anhydrite CaS 4 (b) Extraction : It is obtained by the electrolysis of fused CaCl 2 By adding CaF 2, melting point of CaCl 2 decreases 700 C CaCl 2???? Ca Cl At Cathode (Iron) : Ca e At Anode (Graphite) : 2Cl Ca Cl 2 + 2e (ii) Gold Schmidt (thermite) Process : 3Ca + 2Al Al Ca Ca is reduced by Al because it has greater affinity for oxygen than Ca Note : Unlike Na and K, Calcium cannot be obtanied by the electrolysis of Ca(H Because Ca(H when heated strongly form quicklime which doesnot melt on heating (c) Properties : When heated in a current of C 2, it forms carbide and oxide 5Ca + 2C 2 Heat???? 4Ca + CaC 2 (ii) It absorbs ammonia forming Ca(NH 3 ) 6 which on heating gives calcium amide and then calcium nitride Ca(NH 3 ) 6 (d) Uses : 3Ca(NH 2 Heat???? Ca(NH 2 + 4NH 3 Heat???? Ca 3 N 2 + 4NH 3 For removal of sulphur from petroleium (ii) As dehydrating agent in the preparation of absolute alcohol NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 12

13 NEETIITCM 10 CMPUNDS F CALCIUM 101 Calcium oxide Quick lime, Burnt lime (Ca) 1011 Preparation It is prepared by heating lime stone (Ca ) at 800 C Ca Condition for Good Yield : Ca + C 2 H = 1799 KJ Since the reaction is reversible, therefore the carbon dioxide formed must be removed as soon as it is formed so that the reaction remain in the forward direction (ii) Temperature should not be allowed to rise above 1270K otherwise silica (Si 2 ) present as impurity in limestone will react with Ca to form CaSi Properties Action of water : Ca Ca(H Caloric (quick lime) (Slaked lime) Paste of lime in water is called milk of lime, while its hydrate is known as lime water (ii) With moist chlorine : Ca + Cl 2 CaCl 2 (Bleaching powder) (iii) When heated with carbon, it forms calcium carbide 1013 Uses Ca + 3C In purification of sugar 2000 C????? CaC 2 + C NEETIITCM (ii) As basic lining in furnances 102 Calcium hydroxide, Slaked lime Ca(H 1021 Preparation By the action of water on quick lime Ca Ca(H + Heat means it is an exothermic reaction 1022 Properties Sparingly soluble in water and its solubility decreases with increases in temperature (ii) Action of C 2 : Lime water turns milky on passing C 2 gas Ca(H + C 2 Ca (Milkiness) (iii) Action of chlorine : (a) Cold Condition : Cold 2Ca(H + 2Cl 2???? CaCl 2 + Ca(Cl + 2H 2 (b) Below 35 C : 3Ca(H + 2Cl 2 (Cal Hypochlorite) below?? CaCl 2 35 C?? (c) n gentle Heating : 6Ca(H + 6Cl 2 (d) n Red Hot : 2Ca(H + 2Cl 2 Heat (iv) Action of Ammonia :???? 5CaCl 2 + Ca(Cl 3 + 6H 2 Re d Heat????? 2CaCl 2 + 2H Ca(H + 2NH 4 Cl CaCl 2 + 2NH 3 + 2H Uses For softening of hard water (ii) For purification of sugar and coal gas (iii) In preparation of bleaching powder, white wash, plaster etc 103 Calcium Carbonate (Ca ) 1031 Preparation From slaked lime ; Ca(H + C 2 Ca (ii) From sodium or ammonium carbonate : + CaCl 2 Ca + 2NaCl 1032 Properties 1033 Uses It is a white solid and emits in two crystalline forms ie (a) Calcite (b) Aragonite For manufacturing of cement, washing soda, marble and glass (ii) Used in extraction of metals such as iron (iii) It is used as a constituent of tooth paste NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 13

14 NEETIITCM 104 Calcium Sulphate or Gypsum CaS 4 2H Preparation Ca S 4 CaS 4 + C 2 (ii) CaCl 2 + NaS 4 CaS 4 + 2NaCl 1042 Properties When gypsum is heated to 390K, it changes to a partially hydrated compound known as plaster of paris 2(CaS 4 2H 2 ) 390K???? (CaS 4 H 2 + 3H 2 or CaS H 2 Upon further heating to about 437K it becomes completely anhydrous and is called dead burnt plaster (CaS 4 )H 2 473K???? 2CaS 4 Dead burnt plaster (ii) It forms an important fertilizer (NH 4 S 4 CaS 4 + 2NH 3 + C 2 Ca + (NH 4 S 4 (iii) It forms double salt with ammonium sulphate as CaS 4 (NH 4 S 4 H 2 (iv) Setting of plastar of Paris : n mixing with water it forms a plastic mass which sets into a hard solid in 5-15 min This is called setting of plaster of paris The setting is due to hydration of plaster of paris into gypsum (CaS 4 H 2 + 3H 2 2CaS 4 2H 2 11 CEMENT Gypsum NEETIITCM It is a finely ground mixture of calcium silicates and aluminates which set to a hard mass when treated with water 111 Composition of Cement The average composition of cement is - Ca = 50 to 60%, Mg = 2 3%, Si 2 = 20 25%, Fe 2 3 = 1 2%, Al 2 3 = 5 10%, S 3 = 1 2% For a good quality cement the ratio of silica and alumina (Al 2 3 ) should be between 25 to 40 (ii) If lime is in excess the cement cracks during setting (iii) Water is sprinkled over cement plasters so that needle like cyrstal s of hydrated silicates can form a strong interlocking network 112 Major Components of Cement Tricalcium silicate : 3Ca SI 2 (ii) Dicalcium silicate : 2Ca Si 2 (iii) Tricalcium aluminate : 3Ca Al 2 3 (iv) Tetracalcium aluminate : 4CaAl 2 3 Fe 2 3 Dicalcium silicate is slowest setting component Tricalcium silicate is fastest setting component 113 Raw Materials Limestone provides Ca (ii) Clay provides Al 2 3 and sillica (Si 2 ) (iii) Gypsum CaS 4 2H Preparation The powdered lime stone (3 parts) and clay (1 parts) are mixed The mixture is heated at about K (ii) Following reaction occur : Ca Ca + C 2 2Ca + S 2 2Ca Si 2 (Dicalcium Silicate) 3Ca + Si 2 3Ca Si 2 (Tricalcium Silicate) 3Ca + Al 2 3 3Ca Al 2 3 (Tricalcium Aluminate) 4Ca + Al Fe 2 3 4Ca Al 2 3 Fe 2 3 (Tetra calcium aluminoferrate) Due to very high temp in this zone about 20-30% mass melts and combines with solid mass to form pebbles known as cement clinkers 115 Reinforced Concrete Cement (RCC) When concerete is filled in beams made of iron bars, it is called RCC iron imports extra strength to the structure NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 14

15 NEETIITCM SLVED EXAMPLES Q1 A colourless solid (X) on heating evolved C 2 and also gave a white residue, soluble in water Residue also give C 2 when treated with dilute acid (X) is - (A) (B) Ca (C) NaH (D) Ca(H Sol (1) NaHC Na + H2+C Acid Soluble in C 2 water Q2 C 2 gas along with solid (Y) is obtained when sodium salt (X) is heated (X) is again obtained when C 2 gas is passed into (Y) X & Y are - (A), (B), NaH (C) NaH, (D), NaH 2NaHC Sol (3) 3 (X) Na 2C3 H2 C2 (Y) Heat C3 H2 C2 (Y) 2NaHC 2 (X) Q3 Commercial common salt becomes slightly damp on keeping This is due to the fact that - (A) Common salt is hygroscopic (B) Common salt contains some impurity which is hygroscopic (C) Salt is efflorescent (D) Salt is crystalline Sol (2) Commercial common salt commonly becomes slightly damp on keeping because common salt contains some impurity MgCl 2 and CaCl 2 which is hygroscopic in nature and absorbs moisture from the atmosphere Q4 The highest melting point among alkali metal of - (A) Li (B) Na (C) K (D) Rb Sol (1) Li has highest melting point among alkali metals All alkali metals have low MP The MP decrease down the group The low MP are attributed to their larger atomic size due to which the binding energies of their atoms in the crystal lattice are low Q 5 Li has the maximum value of ionisation potential among alkali metals ie lithium has the minimum tendency to ionise to give Li + ion lithium is - (A) Strongest reducing (B) Poorest reducing agent (C) Strongest oxidising agent (D) Poorest oxidising agent Sol (1) The ionisation potential value of Lithium is maximum among alkali metals ie, its tendency to ionise to give Li + ions should be the minimum ie Li should be the poorest reducing agent But, lithium is the strongest reducing agent This is due to the largest value of hydration energy of Li + ions Q 6 Which of the following compound decomposes at highest temperature - (A) Sr (B) Ba (C) Ca (D) Mg Sol (2) Ba decomposes at highest temp All the carbonates decompose on heating to give C 2 and metal oxide M M + C 2 The stability of carbonate towards heat depends upon the stability of the resulting metal oxide More is the stability of the resulting metal oxide lesser is the stability of the carbonate towards heat and vice versa NEETIITCM NEETIITCM - Free NEET & IIT Study Meterial & Papers Page - 15

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