Chemistry Test - 9

The Bischler-Napieralski reaction is an intramolecular electrophilic aromatic substitution reaction that allows for the cyclization of β-arylethylamides or β-arylethylcarbamates. It was first discovered in 1893 by August Bischler and Bernard Napieralski, in affiliation with Basle Chemical Works and the University of Zurich. The reaction is most notably used in the synthesis of dihydroisoquinolines, which can be subsequently oxidized to isoquinolines.

A mechanism for the Bischler-Napieralski reaction involving a nitrilium intermediate.Two types of mechanisms have appeared in the literature for the Bischler-Napieralski reaction. Mechanism I involves a dichlorophosphoryl imine-ester intermediate, while Mechanism II involves a nitrilium ion intermediate (both shown in brackets). This mechanistic variance stems from the ambiguity over the timing for the elimination of the carbonyl oxygen in the starting amide. In Mechanism I, the elimination occurs with imine formation after cyclization; while in Mechanism II, the elimination yields the nitrilium intermediate prior to cyclization. Currently, it is believed that different reaction conditions affect the prevalence of one mechanism over the other (see reaction conditions).In certain literature, Mechanism II is augmented with the formation of an imidoyl chloride intermediate produced by thesubstitution of chloride for the Lewis acid group just prior to the nitrilium ion.Because the dihydroisoquinoline nitrogen is basic, neutralization is necessary to obtain the deprotonated product.

The particle is γ-ray.

Main Concept :
Neutron proton ratio, Band of stability & Modes of decay 1. The neutron–proton ratio (N/Z ratio or nuclear ratio) of an atomic nucleus is the ratio of its number of neutrons to its number of protons.

2. The ratio generally increases with increasing atomic numbers due to increasing nuclear charge due to repulsive forces of protons.

3. Light elements, up to calcium (Z = 20), have stable isotopes with N/Z ratio of one except for beryllium (n/Z ratio = 1.25), and every element with odd proton numbers from fluorine to potassium. Hydrogen-1 (N/Z ratio = 0) and helium-3 (N/Z ratio = 0.5) are the only stable isotopes with neutron–proton ratio under one.

4. Uranium-238 and plutonium-244 have the highest N/Z ratios of any primordial nuclide at 1.587 and 1.596, respectively, while lead-208 has the highest N/Z ratio of any known stable isotope at 1.537.

5. This causes the radioactivity .

​● Band of stability :

a. It has been found that the stability of nucleus depends upon the neutron to proton ratio (n/p). If we plot the number of neutrons against number of protons for nuclei of various elements, it has been observed that most of the stable (non-radioactive) nuclei lie in a belt shown by shaded region in figure this is called stability belt or stability zone. The nuclei whose n/p ratio does not lie in the belt are unstable and undergo spontaneous radioactive disintegration.

Modes of decay: Rutherford and Soddy, in 1903, postulated that radioactivity is a nuclear phenomenon and all the radioactive changes are taking place in the nucleus of the atom. They presented an interpretation of the radioactive processes and the origin of radiations in the form of a theory known as theory of radioactive disintegration. The main points of this theory are,

● The atomic nuclei of the radioactive elements are unstable and liable to disintegrate any moment.

● The disintegration is spontaneous, i.e., constantly breaking. The rate of breaking is not affected by external factors like temperature, pressure, chemical combination etc.

● During disintegration, atoms of new elements called daughter elements having different physical and chemical properties than the parent elements come into existence.

● During disintegration, either alpha or beta particles are emitted from the nucleus.

● The disintegration process may proceed in one of the following two ways :-

(i) Alpha-particle emission: When an a-particle (₂He⁴) is emitted from the nucleus of an atom of the parent element, the nucleus of the new element, called daughter element possesses atomic mass or atomic mass number less by four units and nuclear charge or atomic number less by 2 units because a-particle has mass of 4 units and nuclear charge of two units.

(ii) Beta-particle emission : b-particle is merely an electron which has negligible mass. Whenever a beta particle is emitted from the nucleus of a radioactive atom, the nucleus of the new element formed possesses the same atomic mass but nuclear charge or atomic number is increased by 1 unit than the parent element. Beta particle emission is due to the result of decay of neutron into proton and electron.  The electron produced escapes as a beta-particle-leaving proton in the nucleus.

(iii) gamma-ray emission : g-rays are emitted due to secondary effects. The excess of energy is released in the form of g-rays. Thus g-rays arise from energy re-arrangements in the nucleus. As g-rays are short wavelength electromagnetic radiations with no charge and no mass, their emission from a radioactive element does not produce new element.

Special case: If in a radioactive transformation 1 alpha and 2 beta-particles are emitted, the resulting nucleus possesses the same atomic number but atomic mass is less by 4 units. A radioactive transformation of this type always produces an isotope of the parent element.

Concept 1 :
Artificial radioactivityThe conversion of one element into another by artificial means, i.e., by means of bombarding with some fundamental particles, is known as artificial transmutation. The phenomenon was first applied on nitrogen whose nucleus was bombarded with a-particles to produce oxygen.

The element, which is produced, shows radioactivity, the phenomenon is known as Induced radioactivity. The fundamental particles which have been used in the bombardment of different elements are,

Since α- particles, protons and deutrons carry positive charge, they are repelled by the positively charged nucleus and hence these are not good projectiles. On the other hand, neutrons, which carry no charge at all, are the best projectiles. Cyclotron is the most commonly used instrument for accelerating these particles. The particles leave the instrument with a velocity of about 25,000 miles per second. A more recent accelerating instrument is called the synchrotron or bevatron. It is important to note that this instrument cannot accelerate the neutrons, being neutral.

When a target element is bombarded with neutrons, product depends upon the speed of neutrons. Slow neutrons penetrate the nucleus while a high-speed neutron passes through the nucleus.

Thus slow neutrons, also called thermal neutrons are more effective in producing nuclear reactions than high-speed neutrons.

ALCHEMY (nuclear transmutation) The process of transforming one element into other is known as alchemy and the person involved in such experiments is called alchemist. Although, gold can be prepared from lead by alchemy, the gold obtained is radioactive and costs very high than natural gold.

Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of another element by a process which occurs either through nuclear reactions (in which an outside particle reacts with a nucleus), or through radioactive decay (where no outside particle is needed). Transmutation technology has the potential to greatly reduce the long-term negative effects of radioactive wastes on human populations by reducing its radioactive half-life.

Synthetic elements : Elements with atomic number greater than 92 i.e. the elements beyond uranium in the periodic table are not found in nature like other elements. All these elements are prepared by artificial transmutation technique and are therefore known as transuranic elements or synthetic elements.

In the Hydrogen Spectrum, Balmer series of transitions in the spectrum of hydrogen atoms fall in the visible region.

All the spectral series of the hydrogen emission spectrum have their limits of wavelength and lie in the specific region of the electromagnetic spectrum. Only the Balmer series lies in the visible region.

Hence the correct answer is (B).

The hard spheres or ion cores touch one another across a face diagonal ⇒ the cube edge length, a = 2R√2

Other Concepts :

Concept 1 :
Important ionic solidsStructure of ionic crystals​

Main Concept :
HybridisationHybridization is a hypothetical concept.  The process of mixing or amalgamation of atomic orbitals of nearly same energy to produce a set of entirely new orbitals of equivalent energy is known as hybridization.

No. of hybrid orbitals formed = No. of atomic orbitals mixed most of the hybrid orbitals are similar but they are not necessarily identical in shape.  They never from π- bonds.

a) The hybridization of carbon in CH₄, C₂H₄ and C₂H₂ is sp³, sp² and sp respectively.  The bond angles are 109.5^o, 120^o and 180^o respectively.

b) The hybridization of O - atom in H₂O and that of N - atom in ammonia is sp³.  The shape of H₂O is V- shape (bent molecule) while that of NH₃ is pyramidal.  The bond angles are 104.5^o and 106.5^o respectively.

c) The hybridization of O - atom in H₃O⁺ ion and that of N - atom in  ion is sp³. The shape of H₃O⁺ is pyramidal while that of  is tetrahedral.

d) Diamond involves sp³ hybridization. It is hard and bad conductor of electricity.  Graphite involves sp² hybridization. It is soft and good conductor of electricity.
Other Concepts :

Concept 1 :
Valence Shell Electron Pair Repulsion theory [VSEPR] for Molecules

The basic concept of the theory was suggested by Sidgwick and Powell (1940). It provides a useful idea for predicting shapes and geometries of molecules. The concept tells that, the arrangement of bonds around the central atom depends upon the repulsion operating between electron pairs(bonded or non bonded) around the central atom. Gillespie and Nyholm developed this concept as valence shell electron pair repulsions (VSEPR) theory. The main postulates of the VSEPR theory are :

(1) For polyatomic molecules containing 3 or more atoms, one of the atoms is called the central atom to which other atoms are linked.

(2) The geometry of a molecule depends upon the total number of valence shell electron pairs (bonded or not bonded) present around the central atom and their repulsion due to relative sizes and shapes.

(3) If the central atom is surrounded by bond pairs only, then it gives the symmetrical shape to the molecule.

(4) If the central atom is surrounded by lone pairs (lp) as well as bond pairs (bp) of electrons then the molecule has a distorted geometry (unsymmetrical shape).

(5) The relative order of repulsion between electron pairs is as follows : 

A lone pair is concentrated around the central atom while a bond pair is pulled out between two bonded atoms. As such repulsion becomes greater when a lone pair is involved.

Lone pair-bond pair and their respective shapes table

Step1: Visualise lp - lp repulsion

Lone pair-lone pair repulsion is strongest because they are free moving electrons so they will move as far away from each other as possible.

Step2: Visualise lp - bp repulsion

Bonding pair-lone pair repulsion is not as strong because the bonding pair is not free moving, therefore, will not be repelled.

Step3: Visualise bp - bp repulsion

Bonding pair-bonding pair repulsion is weakest because they are bound to the covalent bonds. They cannot move away from each other because they must stay in the region between two atoms.

Step4: Now after analysing all the above 3 steps arrange them accordingly .

Concept 3 :
Hybridisation of Atomic Orbitals sp, sp², sp³, sp³d, sp³d², dsp² and sp³d³.

The concept of hybridization was introduced by Pauling and Slater.

Hybridization: It is defined as the intermixing of dissimilar orbitals of the same atom but having slightly different energies to form same number of new orbitals of equal energies and identical shapes. The new orbitals so formed are known as hybrid orbitals.

How to determine type of hybridization: The structure of any molecule can be predicted on the basis of hybridization which in turn can be known by the following general formulation,

Where; H = Number of orbitals involved in hybridization viz. 2, 3, 4, 5, 6 and 7, hence nature of hybridization will be sp, sp², sp³, sp³d, sp³d², sp³d³ respectively.
V = Number of electrons in valence shell of the central atom,
M = Number of monovalent atom
C = Charge on cation,
A = Charge on anion

Characteristics of hybridization:
(1) Only orbitals of almost similar energies and belonging to the same atom or ion undergoes hybridization.
(2) Hybridization takes place only in orbitals, electrons are not involved in it.
(3) The number of hybrid orbitals produced is equal to the number of pure orbitals, mixed during hybridization.
(4) In the excited state, the number of unpaired electrons must correspond to the oxidation state of the central atom in the molecule.
(5) Both half filled orbitals or fully filled orbitals of equivalent energy can involve in hybridization.
(6) Hybrid orbitals form only sigma bonds.
(7) Orbitals involved in pi bond formation do not participate in hybridization.
(8) Hybridization never takes place in an isolated atom but it occurs only at the time of bond formation.

Geometric Arrangements Charactristic of Hybrid Orbital Sets

Main Concept :
Unique value of reaction rate A reaction rate can be reported quite differently depending on which product or reagent selected to be monitored.

Given a reaction:

Even though the concentrations of A, B, C and D may all change at different rates, there is only one average rate of reaction. To get this unique rate, choose any one rate and divide it by the stoichiometric coefficient. When the reaction has the formula:

Rate law expressionThe rate law or rate equation for a chemical reaction is an equation that links the reaction rate with concentrations or pressures of reactants and constant parameters (normally rate coefficients and partial reaction orders). For many reactions the rate is given by a power law such as

r = k[A]^x [B]^y

Where [A] and [B] express the concentration of the species A and B, respectively (usually in moles per liter (molarity, M)). The exponents x and y are the partial reaction orders and must be determined experimentally; they are often not equal to the stoichiometric coefficients. The constant k is the rate coefficient or rate constant of the reaction.

Since the concentration of A decreases, teh change in its concentation is negative. It is multiplied by -1 to obtain the rate of reaction which is always a positive quantity. The rate obtained from Eqs. 1 and 2 is called the average rate of reaction and is represented as r avg. It depends on the time interval between which is measured and the concentration of reactants and products.

It depends on the time interval between which is measured and the concentration of reactants and products.

The rate at which a reactant is being consumed at any particular moment is called the instantaneous rate. Mathematically, the instantaneous rate can be determined by measuring the average rate in the smallest time interval dt (i.e., as Δt approaches zero). Thus for the reaction A ⟶ B , the instantaneous rate can be expressed using average rate as

Graphically, the two rates may be represented as shown in diagram.

Note: When we use the term “reaction rate” we mean instantaneous rate, unless stated otherwise.

For reaction in which the stoichiometric coefficients of the reactants and products are the same, as in decomposition of thionyl chloride (SO₂Cl₂), the rate of appearance of the products.

Example: The rate of reaction is equal to the change in the phenolpthalein concentration divided by the length of time over which the change occurs.

Two optically active forms are possible for a compound of following structural formula

Main Concept :

Concept of Enantiomers Enantiomer: The optically active entity which is non-superimposable on its mirror image is called as enantiomer to each other.

Bigger cation stabilizes  bigger anion. i.e.

$\mathrm{M}\mathrm{g}{\left(\mathrm{O}\mathrm{H}\right)}_2<\mathrm{C}\mathrm{a}{\left(\mathrm{O}\mathrm{H}\right)}_2<\mathrm{S}\mathrm{r}{\left(\mathrm{O}\mathrm{H}\right)}_2<\mathrm{B}\mathrm{a}{\left(\mathrm{O}\mathrm{H}\right)}_2$

So solubility decreases as strength of bonding between ions increases
Main Concept :
Examples on Fajan's Rule, Covalent Bond Characteristics

Fajans Rule: The magnitude of polarization or increased covalent character depends upon a number of factors. These factors are,

(1) Small size of cation: Smaller the size of cation, greater is its polarizing power i.e. greater will be the covalent nature of the bond.

(2) Large size of anion: Larger the size of anion, greater is its polarizing power i.e. greater will be the covalent nature of the bond.

(3) Large charge on either of the two ions: As the charge on the ion increases, the electrostatic attraction of the cation for the outer electrons of the anion also increases with the result its ability for forming the covalent bond increases.

(4) Electronic configuration of the cation: For the two ions of the same size and charge, one with a pseudo noble gas configuration (i.e. 18 electrons in the outermost shell) will be more polarizing than a cation with noble gas configuration (i.e., 8 electron in the outer most shell).

For example,
 

Question: What is the bond character of SnCl₄?

Solution:

Step1: Think about the size of cation and anion

Step2: If the cation is small with large positive charge and large anion

Step3: Then the bond character is covalent.

Sn⁴⁺ is a small cation with high positive charge, and is a large anion, as already stated. Therefore, according to the rules, SnCl₄ is the tin halide with more covalent charactor.

Other Concepts :

Concept 1 :
Chemical properties of Alkaline earth metals

$2M+O_2\to 2\mathit{MO}(\mathit{M\; is\; Be},\mathit{Mg\; or\; Ca})$

$2M+O_2\to M{O}_2\mathit{}\left(\mathit{M\; is\; Ba\; or\; Sr}\right)$

(ii) Their less reactivity than the alkali metals is evident by the fact that they are slowly oxidized on exposure to air, However the reactivity of these metals towards oxygen increases on moving down the group.
(iii) The oxides of these metals are very stable due to high lattice energy.
(iv) The oxides of the metal (except BeO and MgO) dissolve in water to form basic hydroxides and evolve a large amount of heat. BeO and MgO possess high lattice energy and thus insoluble in water.
(v) BeO dissolves both in acid and alkalies to give salts i.e. BeO possesses amphoteric nature.

$BeO+2NAOH\to \underset{Sod.\text{}Beryllate}{NaBe{O}_2}+H_{2}O;$

$BeO+2HCl\to \underset{BerylliumChloride}{BeC{l}_2}+H_{2}O$

(vi)The basic nature of oxides of alkaline earth metals increases from Be to Ra as the electropositive Character increases from Be to Ra.
(vii)The tendency of these metal to react with water increases with increase in electropositive character i.e. Be to Ra.
(viii) Reaction of Be with water is not certain, magnesium reacts only with hot water, while other metals react with cold water but slowly and less energetically than alkali metals.
(ix) The inertness of Be and Mg towards water is due to the formation of protective, thin layer of hydroxide on the surface of the metals.
(x) The basic nature of hydroxides increase from Be to Ra. It is because of increase in ionic radius down the group which results in a decrease in strength of M –O bond in M –(OH)₂ to show more dissociation of hydroxides and greater basic character.
(xi) The solubility of hydroxides of alkaline earth metals is relatively less than their corresponding alkali metal hydroxides Furthermore, the solubility of hydroxides of alkaline earth metals increases from Be to Ba. Be (OH)₂ and Mg (OH)₂ are almost insoluble, Ca (OH)₂ (often called lime water) is sparingly soluble whereas Sr(OH)₂ and Ba (OH)₂ (often called baryta water) are more soluble.

The trend of the solubility of these hydroxides depends on the values of lattice energy and hydration energy of these hydroxides. The magnitude of hydration energy remains almost same whereas lattice energy decreases appreciably down the group leading to more –Ve values for $\Delta H_{solution}$ down the group.

$\Delta H_{solution}=\Delta H_{latticeenergy}+\Delta H_{hydrationenergy}$

More negative is $\Delta H_{solution}$ more is solubility of compounds.

(xii) The basic character of oxides and hydroxides of alkaline earth metals is lesser than their corresponding alkali metal oxides and hydroxides.
(xiii) Aqueous solution of lime water [Ca(OH)₂] or baryta water [Ba(OH)]₂ are used to qualitative identification and quantative estimation of carbon dioxide, as both of them gives white precipitate with CO₂ due to formation of insoluble CaCO₃ or BaCO₃

$\mathit{Ca}{\left(\mathit{OH}\right)}_2+C{O}_2\to \mathit{CaC}{O}_3+H_{2}O;\mathit{Ba}{\left(\mathit{OH}\right)}_2+C{O}_2\to \mathit{BaC}{O}_3+H_{2}O$
                                    (white ppt)                                                  (white ppt)

SO₂ also give white ppt of CaSO₃ and BaSO₃ on passing through lime water or baryta water. However on passing CO₂ in excess, the white turbidity of insoluble carbonates dissolve to give a clear solution again due to the formation of soluble bicarbonates,

$\mathit{CaC}{O}_3\to H_{2}O+C{O}_2\to \mathit{Ca}{\left(\mathit{HC}{O}_3\right)}_2$

(2) Hydrides

(i) Except Be, all alkaline earth metals form hydrides (MH₂) on heating directly with H₂ .

$M+H_2\to M{H}_2$

(ii) BeH₂ is prepared by the action of LiAlH₄ on BeCl₂

$2\mathit{BeC}{l}_2+\mathit{LiAl}{H}_4\to 2\mathit{Be}{H}_2+\mathit{LiCl}+\mathit{AlC}{l}_3$

(iii) BeH₂ and MgH₂ are covalent while other hydrides are ionic.
(iv) The ionic hydrides of Ca, Sr, Ba liberate H₂ at anode and metal at cathode.

$Ca{H}_2\stackrel{fusion}{\rightleftharpoons }C{a}^{2+}+2H^{–}$

Anode: $2H^{–}\to H_2+2e^{–}$    Cathode:$C{a}^{2+}+2e^{–}\to \mathit{Ca}$

(v) The stability of hydrides decreases from Be to Ba.
(vi) The hydrides having higher reactivity for water, dissolves readily and produce hydrogen gas.

$\mathit{Ca}{H}_{2\left(S\right)}+2H_{2}O\to \mathit{Ca}{\left(\mathit{OH}\right)}_2+2H_2\uparrow$

(3) Carbonates and Bicarbonates
(i) All these metal carbonates (MCO₃) are insoluble in neutral medium but soluble in acid medium. These are precipitated by the addition of alkali metal or ammonium carbonate solution to the solution of these metals.

${\left(N{H}_4\right)}_{2}C{O}_3+\mathit{CaC}{l}_2\to 2N{H}_4\mathit{Cl}+\mathit{CaC}{O}_3$

$N{a}_{2}C{O}_3+\mathit{BaC}{l}_2\to 2\mathit{NaCl}+\mathit{BaC}{O}_3$

(ii) Alkaline earth metal carbonates are obtained as white precipitates when calculated amount of carbon dioxide is passed through the solution of the alkaline metal hydroxides.

$M{\left(\mathit{OH}\right)}_{2\left(\mathit{aq}\right)}+C{O}_{2\left(g\right)}\to \mathit{MC}{O}_{3\left(S\right)}+H_2{O}_{\left(l\right)}$

and sodium or ammonium carbonate is added to the solution of the alkaline earth metal salt such as CaCl₂.

$\mathit{CaC}{l}_{2\left(\mathit{aq}\right)}+N{a}_{2}C{O}_{3\left(\mathit{aq}\right)}\to \mathit{CaC}{O}_{3\left(S\right)}+2\mathit{NaC}{l}_{\left(\mathit{aq}\right)}$

(iii) Solubility of carbonates of these metals also decreases downward in the group due to the decrease of hydration energy as the lattice energy remains almost unchanged as in case of sulphates.
(vi) The carbonates of these metals decompose on heating to give the oxides, the temperature of decomposition increasing from Be to Ba. Beryllium carbonate is unstable.

$MC{O}_3\stackrel{Heat}{\to }MO+C{O}_2$

(4) Halides

(i) The alkaline earth metals combine directly with halogens at appropriate temperatures forming halides, MX₂. These halides can also be prepared by the action of halogen acids (HX) on metals, metal oxides, hydroxides and carbonates.

$M+2\mathit{HX}+M{X}_2+H_2;\mathit{MO}+2\mathit{HX}\to M{X}_2+H_{2}O$

$M{\left(\mathit{OH}\right)}_2+2\mathit{HX}\to M{X}_2+2H_{2}O$

$\mathit{MC}{O}_3+2\mathit{HX}\to M{X}_2+C{O}_2+H_{2}O$

Beryllium chloride is however, conveniently obtained from oxide

$BeO+O+C{l}_2\stackrel{870–1070K}{\to }BeC{l}_2+CO$

(ii) BeCl₂ is essentially covalent, the chlorides MgCl₂, CaCl₂ , SrCl₂ and BaCl₂ are ionic; the ionic character increases as the size of the metal ion increases. The evidence is provided by the following facts,
(a) Beryllium chloride is relatively low melting and volatile whereas BaCl₂ has high melting and stable.
(b) Beryllium chloride is soluble in organic solvents.
(iii) The halides of the members of this group are soluble in water and produce neutral solutions from which the hydrates such : MgCl₂ 6H₂O, CaCl₂.6H₂O. BaCl₂ 2H₂O can be crystallised. The tendency to form hydrated halides decreases with increasing size of the metal ions.
(iv) BeCl₂ is readily hydrolysed with water to form acid solution, $\mathit{BeC}{l}_2+2H_{2}O\to \mathit{Be}{\left(\mathit{OH}\right)}_2+2\mathit{HCl.}$

(v) The fluorides are relatively less soluble than the chlorides due to high lattice energies. Except BeCl₂ and MgCl₂ the chlorides of alkaline earth metals impart characteristic colours to flame.

CaCl₂                            SrCl₂                                  BaCl₂
Brick Red Colour         Crimson Colour           Grassy Green Colour
 
Structure of BeCl₂ : In the solid phase polymeric chain structure with three centre two electron bonding with Be-Cl-Be bridged structure is shown below,


 

(iii) These nitrides are hydrolysed water to liberate

$M_3{N}_2+6H_{2}O\to 3M{\left(\mathit{OH}\right)}_2+2N{H}_3$

(7) Sulphates
(i) All these form sulphate of the type M SO₄ by the action of H₂ SO₄ on metals, their oxides, carbonates or hydroxides.

$M+H_{2}S{O}_4\to \mathit{MS}{O}_4+H_2;\mathit{MO}+H_{2}S{O}_4\to \mathit{MS}{O}_4+H_{2}O$

$\mathit{MC}{O}_3+H_{2}S{O}_4\to \mathit{MS}{O}_4+H_{2}O+C{O}_2$

$M{\left(\mathit{OH}\right)}_2+H_{2}S{O}_4\to \mathit{MS}{O}_4+2H_{2}O$

(ii) The solubility of sulphates in water decreases on moving down the group. BeSO₄ and MgSO₄ are fairly soluble in water while BaSO₄ is completely insoluble. This is due to increases in lattice energy of sulphates down the group which predominates over hydration energy.
(iii) Sulphates are quite stable to heat however, reduced to sulphide on heating with carbon.

$\mathit{MS}{O}_4+2C\to \mathit{MS}+2C{O}_2$

(8) Action with carbon : Alkaline metals (except Be, Mg) when heated with carbon form carbides of the type MC₂ These carbides are also called acetylides as on hydrolysis they evolve acetylene.

$M{C}_2+2H_{2}O\to M{\left(\mathit{OH}\right)}_2+C_2{H}_2$

(10) Nitrates : Nitrates of these metals are soluble in water On heating they decompose into their corresponding oxides with evolution of a mixture of nitrogen dioxide and oxygen.

$M{\left(N{O}_3\right)}_2\to \mathit{MO}+2N{O}_2+\left(\frac{1}{2}\right)O_2$