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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 351. |
Match the list of noble gas compounds in column I with their shapes in column II and mark the appropriate choice. A. `(A) rarr (iv), (B) rarr (iii), (C) rarr (ii), (D) rarr (i)`B. `(A) rarr (i), (B) rarr (ii), (C) rarr (iii), (D) rarr (iv)`C. `(A) rarr (ii), (B) rarr (iii), (C) rarr (iv), (D) rarr (i)`D. `(A) rarr (iii), (B) rarr (i), (C) rarr (iv), (D) rarr (ii)` |
| Answer» Correct Answer - D | |
| 352. |
Oganesson has been synthetically produced by collision ofA. Ra and CaB. Cf and CaC. Cf and CuD. Ra and He |
| Answer» Correct Answer - B | |
| 353. |
Which of the following is not correct about xenon hexafluoride? A. It has oxidation state of +6.B. The hybridisation involved in `XeF_(6)" is "sp^(3) d^(3)`C. The shape of `XeF_(6)` is distorted octahedral and can be represented asD. On hydrolysis it gives `Xe, HF and O_(2).` |
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Answer» Correct Answer - D On hydrolysis the products formed are `XeO_(3) and HF`. `XeF_(6)+3H_(2)OrarrXeO_(3)+6HF` |
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| 354. |
Which of the following is not a use of noble gases?A. Argon is widely used for filling incandescent electric bulbs.B. Neon is used in safety devices for protecting electrical instruments.C. Radon is used in radiotherapy of cancer.D. Helium is filled in tubes of cycles and scooters tyres. |
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Answer» Correct Answer - D Helium is used in filling tubes of aeroplane tyres. |
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| 355. |
Why m.p. and b.p. of group 14 elements are higher in comparison to group 13? |
| Answer» Due to covalent bond (strong binding forces) | |
| 356. |
Name the type of bonding in lead. |
| Answer» Correct Answer - Metallic | |
| 357. |
Name the type of bonding in `SnF_(4)` and `PbF_(4)`. |
| Answer» Correct Answer - Ionic | |
| 358. |
Which of the following is a Lewis acid ?A. `AlCl_(3)`B. `MgCl_(2)`C. `CaCl_(2)`D. `BaCl_(2)` |
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Answer» Correct Answer - A Alkaline earth metals form ionic chloride whereas aluminium chloride is covalent. Despite of sharing electrons with chlorine, the octet of aluminium is incomplete. To complete the octet, it needs electrons and thus, acts as a Lewis acid `._(13)Al = 2,8,3 and ._(17)Cl = 2,8,7` `{:(" "Cl),(" |"),(Cl-Al-Cl),(" "uarr),("Octet incomplete"):}`. |
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| 359. |
On heating the viscosity of liquid sulphur areA. incrasesB. decreasesC. first increasea and then decreasesD. first decrease and the n increase |
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Answer» Correct Answer - 2 Both rhombic and monoclinic sulphur melt to forms a low-visosity straw-colord liquid. Owing to the conversion of rhomble to monocline sulphure,and also to possible variations in the percentage ofa llotropes of liquid sulphur formed,the melting points are not sharp, rhombic sulphur melts at approxmately `113^(@)C` whist monoclinic sulphur at approximately `119^(@)C`. But when the liquid is heated, there is an abrupt change in propertics at `159^(@)C`. The most dramatic transformation is a `10^(4)`-fold increases in visosity.The liquid also darkness considerably until it is nearly black and becomes viscous. We can explain these change in terms of a rupture of the `S_(8)` rings . The octasulphur chain then link one to another to form polymers containing as many as `20,000 S` atoms. Thus, the rise in viscocity is explained by a replacement of the free-moving `S_(8)` molecules by these interwined chains, which have strong dispersion force interactions. The viscosity increases sharply abd continue to rise up to`200^(@)C`. At about `200^(@)C` the viscosity begins to fall and at its boiling point of `445^(@)C` the liquids is again mobile. When sulphur vapour come in contact with a cool surface it sublimes to give a pale yellow solid. The drcreases in viscosity of liquid sulphur that occurs above `200^(@)C` is explained as being due to the breakdown of these long chains and the reforming fo `S_(8)` rinds. Sulphur vapour contains `S_(8)` rings ,together with small fragments such as `S_(6),S_(4)` consist of `S_(2)` molecules. At `600^(@)C` the gas mainly consists of `S_(2)` molecules. At very high temperatures,atomic sulphur is formed. The `S_(2)` molecules is paramagnetic and blue colored like `O_(2)` and prsumably has similarly bonding. `S_(2)` gas is stable up to `2200^(@)C` .The stability of `S_(2)` is used in the quantitative analysis of `S` compounds. They are burnt in a reducing flame, and the color from excited `S_(2)` is measured spactrophotometrically .`S_(3)` and `S_(4)` are also known . |
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| 360. |
In the cyclo `-S_(8)` molecule of rhombic sulphur, all the `S-S` bond lengths and all the `S-S-S` bond angle are `"_____"` (approximate values ) respectivelyA. `204`pm and `105^(@)`B. `204`pm and `107^(@)`C. `102`pm and `102^(@)`D. `102`pm and `106^(@)` |
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Answer» Correct Answer - 2 In all of the ring forms of `S`,the `S-S` distance is `204-2.6p m` and the bond angle `S-S-S` in the range `102-108^(@)`. They are all soluble in `CS_(2)`. Orthorhombic form of `S` is thermodynamically and most stable. |
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| 361. |
Which of the following is incorrect regarding ozone?A. it is oxidized `H_(2)S` to `SO_(2)`B. it oxidized alkaline `KI` to potassium iodate or to potasium periodate depending upon the amountC. its oxidizes dry iodine to `I_(4)O_(9)` a yellow powerD. silver metal is blackened by ozone. |
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Answer» Correct Answer - 1 `H_(2)S` is oxidized to sulphur `H_(2)S+O_(3)rarrH_(2)O+S+O_(2)` Silver metal is blackened due to alternate oxidation of the metal and reduction of oxide `2Ag+O_(3)rarrAg_(2)O+O_(2)` `Ag_(2)O+O_(3)rarr2Ag+2O_(2)` Other reaction are `KI+3O_(3)rarr KIO_(3)+3O_(2)` `KI+4O_(3)rarrKIO_(4)+4O_(2)` `O_(3)rarrO_(2)+O]xx9` `(2I_(2)+9Orarr I_(4)O_(9))/(2I_(2)+9O_(3)rarr I_(4)O_(9)+9O_(2))` |
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| 362. |
Which of the following is a the most preferred and hence of the lower energy for `SO_(3)`?A. B. C. D. |
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Answer» Correct Answer - 1 In this structure sulphur atom forms the maximum number of covalent bonds which results into lowest energy for `SO_(3)`. |
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| 363. |
Which one is the active constituent of bleaching powder?A. `CaCI_(2)`B. `CaOCl_(2)`C. `Ca(OCI)_(2)`D. `CaO_(2)Cl` |
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Answer» Correct Answer - 3 Bleaching poeder (also called chloride of line) is a whitish powder, consisting mainly of calcium hypochlorite, `Ca(Ocl)_(2)`. It is prepared by the action of chlorine on a suspension of calcium hydoxide: `2Cl_(2)(g)+2Ca(OH)_(2)(s) rarr Ca(OCl)_(2).2H_(2)O(s)+CaCl_(2)(aq.)` the action of dilute acids liberates chlorine, which acts as an oxidizing agent and so bleaches the material. |
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| 364. |
Carbon is an essential constituent of all living matter such asA. fatsB. carbohydratesC. proteinsD. all of these |
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Answer» Correct Answer - D Fats and oils are simple lipids consisting of mixtures of various glycerides of fatty acids, which occur in plants an animals and serve as storage materials. Carbohydrates are a large group of organic compounds composed of `C, H` and `O` only, usually with the general formula `C_(X)(H_(2)O)_(Y)`. Protein molecules consist of hundreds of thousands of amino acids jointed together by the peptide linkage. |
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| 365. |
Which of the following exists as a cyclic tetramer in the solid state?A. `SO_(3)`B. `SeO_(3)`C. `TeO_(3)`D. `PoO_(3)` |
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Answer» Correct Answer - 2 `SO_(3)` in the gas phase exists as planar triangular molecules species.In the solid state, `SO_(3)` exist in serveral modification having a linear cyclic trimetric or a polymeric chain structure.On the other hand ,`SeO_(3)` exists as a cyclic tetramer `(Se_(4)O_(12))` in the solid state`TeO_(3)` is also a solid with a network structure in which `TeO_(6)` octahedral share all vetices. |
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| 366. |
When exposed to ultraviolet radiatoin ( for example, from fluorescent lights), the white phosphorus slowly turns toA. black `P`B. yellow `P`C. Violet `P`D. red `P` |
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Answer» Correct Answer - 4 If white `P` is heated to about `250^(@)C` or a lower temperature in the presence of sunlight ,then red `P` is formed. This is a polymetic solid, which is much less reactive than white phosphorus. Violet `P` is formed by heating a solution red `P` in molten lead to `500^(@)C` ,and black `P`, is formed by heating white `P` under a pressure thousands of times atmosphere. |
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| 367. |
Which of the following in incorrect?A. `H_(2)SO_(4)` reach with `PCl_(5)` to produces `SO_(2)Cl_(2)`B. `K_(4)[Fe(CN)_(6)]` reacts with concentrated `H_(2)SO_(4)` to produces `CO_(2)`C. Solid `KCIO_(3)` on heating with concentrated `H_(2)SO_(4)` produces `CIO_(2)`D. `H_(2)SO_(4)` forms `SO_(3)` on treatment with phosphorous pentoxides |
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Answer» Correct Answer - 2 On heating potassium ferroeyanide with concentrated `H_(2)SO_(4),Co` is evolved: `K_(4)Fe(CN)_(6)+6H_(2)SO_(4)+6H_(2)Orarr2K_(2)SO_(4)+FeSO_(4)+3(NH_(4))_(2)SO_(4)+6CO` One or both the hydroxyl groups can be replaced by `Cl` on treatment with `PCl_(5)` On heating potassium chlorate with concentrated sulphuric acid, chloride dioxide is evolved with explosion: `2KClO_(3)+3H_(2)SO_(4)rarr3KHSO_(4)+HClO_(4)+2ClO_(2)+H_(2)O` Dehydration of concentrated `H_(2)SO_(4)` in ht epresence of `P_(4)O_(10)` Produces `SO_(3)`: `H_(2)SO_(4)+P_(2)O_(5)rarr2HPO_(3)+SO_(3)`. |
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| 368. |
Which of the following gives dioxygen and metal on heating?A. `BaO_(2)`B. `Ag_(2)O`C. `MnO_(2)`D. `Pb_(3)O_(4)` |
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Answer» Correct Answer - 2 We can obtain dioxygen by (i) thermal decomposition of the oxides of matel which are low in the electrochemical series: `2HgOoverset(450^(@)C)rarr2Hg+O_(2)` `2Ag_(2)O overset(350^(@)C)rarr4Ag+O_(2)` (ii) the thermal deocmpositonof higer oxides: `2Pb_(3)O_(4)overset(Delta)rarr6PbO+O_(2)` `2PbO_(2)overset(Delta)rarr2PbO+O_(2)` `3MnO_(2)overset(Delta)rarrMn_(3)O_(4)+O_(2)` (iii) the thermal decomposition of peroxides: `2BaO_(2)overset(Delta)rarr2BaO+O_(2)` |
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| 369. |
Which of the following compounds is exceptionally stable for steric reasons?A. `SF_(4)`B. `TeF_(6)`C. `SF_(6)`D. `SeF_(6)` |
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Answer» Correct Answer - 3 Sulpher hexafluoride `(SF_(6)` which contains`6-`valent sulpher is chemically intert towards fused alkali and oxygen. Because of its inertness and good dielectric properties it is used as a gaseous insulator in high voltage generators. However, the very inertness of `SF_(6)` makes ot a particular problem in the context of climate impact. The gas absorbs radiation throughout much of hte otherwise transparent part of the infrated region int he atmsophere. As a result ,it is anextraordinary effectives greenhouses gas, `1` tonnes of `SF_(6)` being equivalent to `23,900` tonnes of `CO_(2)` in terms of infrared absoption. |
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| 370. |
`NaOH` gives disproportionation reaction with |
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Answer» The reaction is disproportionation in nature because chlorine undergoes decrease as well as increase in oxidation states. `overset(O)Cl_(2)+2NaOH overset("Cold") to Na overset(-1)(Cl)+Na overset(+1) (ClO)+H_(2)O` `overset(O) (Cl_(2)) +6NaOH overset("Hot") to 5Na overset(-1)(Cl)+Na overset(+5)(ClO_(3)) +3H_(2)O` |
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| 371. |
When chlorine water is exposed to sun light, the colour change which occurs is from :A. colourless to brwonB. brown to colourlessC. light blue to colourlessD. greenish yellow to colourless |
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Answer» Correct Answer - D `underset("yellow")underset("Greenish")(Cl_(2))+H_(2)O to underset("Colourless")(2HCl+(O))` |
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| 372. |
Which of the following reaction is not feasible?A. `2KI + Br_(2) to 2KBr +I_(2)`B. `2KBr + I_(2) to 2KI+ Br_(2)`C. `2KBr + Cl_(2) to 2KCl + Br_(2)`D. `2H_(2)O + 2F_(2) to 4HF + O_(2)` |
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Answer» Correct Answer - B `I_(2)` cannot replace `B_(2)` from KBr solution. |
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| 373. |
The reaction between urea and nitrous acid producesA. `N_(2)O`B. `N_(2)`C. `NO_(2)`D. `NH_(3)` |
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Answer» Correct Answer - 2 Nitrogen may be obtained in the elementary form by heating urea with nitrous acid. `underset("Urea")(H_(2)NCONH_(2))+2NHO_(2)rarr2N_(2)+CO_(2)+3H_(2)O` Nitrous acid is unstable and is always prepared in situ by the action of dilute sulphuric acid on sodium or potassium nitrite. |
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| 374. |
Which of the following is an exothermic compound?A. `SbH_(3)`B. `AsH_(3)`C. `PH_(3)`D. `NH_(3)` |
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Answer» Correct Answer - 4 The thermal stability of the hydrides decreases as we move from `NH_(3)` to `BiH_(3)` on account of the decrease of `E-H` bond strength. Only `NH_(3)` has negative `Delta_(f)H^(Ɵ)` whilst all other hydrides have positive `Delta_(f)H^(Ɵ)` |
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| 375. |
Combustion of hydrazine producesA. `NH_(2)OH`B. `N_(2)`C. `N_(2)O`D. `N_(2)O_(5)` |
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Answer» Correct Answer - 2 Hydrazine is a covalent liquid, which fumes in air, and smells similar to`NH_(3)`. Pure hydrazine burns readily in air with the evolution of a large amount of heat. `N_(2)H_(4)(l)+O_(2)(g)rarrN_(2)(g)+2H_(2)O(l)DeltaH=-621" KJ mol"^(-1)` |
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| 376. |
Which of the following is correct for the azide `(N_(3)^(-))` ion?A. it is constidered as a pseufohalide ionB. Analysis fo `N_(3)^(-)` is by reduction with `H_(2)S`C. The `N_(3)^(-)` ion has `16` outer electorns and is isoelectronic with `CO_(2)`D. all of these |
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Answer» Correct Answer - 4 It forms the extremely unstable and explosive compounds fluorazide `FN_(3)`, chlorazide `ClN_(3)`, bromazide `BrN_(3)` and iodazide`IN_(3)` but the dimer `N_(3)-N_(3)` is unknown `NaN_(3)+H_(2)S+H_(2)OrarrNH_(3)+N_(2)+S+NaOH` The `N_(3)^(-)` ion is linear `(N-N-N)` as is `CO_(2)` . |
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| 377. |
Which of the following reactions are feasible for hydrazine?A. `N_(2)H_(4)+2CusO_(4)rarrCu+N_(2)+2H_(2)SO_(4)`B. `N_(2)H_(4)+2O_(2)rarr2H_(2)O_(2)+N_(2)`C. `N_(2)H_(4)+2I_(2)rarr4HI+N_(2)`D. all of these |
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Answer» Correct Answer - 4 When dissolved in water (in neutral or basic solutions ) hydrazine or its salts are powerful reducing agents. They are used to produce silver and copper mirrors and to precipitate the platinum metals. Hydrazine also `I_(2)` reduces and `O_(2)` |
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| 378. |
`Zn` gives `H_(2)` gas with `H_(2)SO_(4)` and`HCI` but not with `HNO_(3)`becauseA. `Zn` acts a oxidies agent where it reacts with `HNO_(3)`B. `HNO_(3)` is a weaker acid than `H_(2)SO_(4)` and `HCl`C. `Zn ` is placed above hydrogen in electrochemical series.D. `NO_(3)^(-)` is reduced in preference to hydronium ion |
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Answer» Correct Answer - 3 `Zn` liberates `H_(2)` gas from dilute `HCl//H_(2)SO_(4)` as it is presetn aboce `H` in electrochemical series `[E_(Zn^(2+)//Zn)^(Ɵ) lt E_(H^(+)//H_(2))]` But `HNO_(3)` is an oxidising agent thus hydrogen gas released initially gets oxidized to `H_(2)` ol while `NO_(3^(-)` is reduced : ` Zn +2HNO_(3)rarr Zn(NO_(3))_(2)+2H]xx4` `(~60%)` `{:(HNO_(3)+8H rarr NH_(3)+3H_(2)O),(NH_(3)+HNO_(3) rarr NH_(4)NO_(3)),(bar(4Zn+10HNO_(3) rarr 4Zn(NO_(3))_(2)+NH_(4)NO_(3)+3H_(2)O)):}` |
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| 379. |
Which of the following reaction is not feasible?A. `2KI+Br_(2)rarr2KBr+I_(2)`B. `2KBr+I_(2) rarr 2KI+Br_(2)`C. `2KBr+Cl_(2)rarr2KCl+Br_(2)`D. `2H_(2)O+2F_(2)rarr4HF+O_(2)` |
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Answer» Correct Answer - 2 A halgen `(X_(2))` of lower atomic number can displace other halgons of higher atomic number from their salts `(X)^(-)` thus following reaction: `2KBr+I_(2)rarr2KI+Br_(2)` is not possible `E_(I_(2)//I^(-))^(Ɵ) lt E_(Br_(2)//Br^(-))^(Ɵ)` |
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| 380. |
What happens when phosphorus acids `(H_(3)PO_(3))` is heated ? |
| Answer» Disproportionation occurs `4H_(3)PO_(3)to3H_(3)PO_(4)+PH_(3)` | |
| 381. |
Elements in which the last electron enters any one of the three `p` orbitals of their respective ________ shells are called `p`-block elements.A. penultimateB. antepenultimateC. outermostD. foremost |
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Answer» Correct Answer - C The differentiating electron goes to the `p`-subshell of the last shell. |
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| 382. |
Which of the following statements regarding sulphur is incorrect?A. `S_(2)` molecule is paramagnetic.B. The vapours the `200^(@)C` consist mostly of `S_(8)` rings.C. At `600^(@)C`, the gas mainly consists of `S_(2)` molecules.D. The oxidation state of sulphur is never less than `+4` in its compounds. |
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Answer» Correct Answer - D Sulphur exhibits oxidation states of `-2,+2,+4 " and " +6` in its compounds |
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| 383. |
Which halogen has tendency to form cation ? |
| Answer» Correct Answer - Iodine. | |
| 384. |
Which of the following is a nitric acid anhydride? |
| Answer» Correct Answer - `N_(2)O_(5)` | |
| 385. |
Which of the following statement is false?A. The must abundant rare gs found in the atomspher is heliumB. Xenon is the most reactive among the rare gasesC. Helium is inert gasD. Radon is obtained form the decay of radium |
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Answer» Correct Answer - 1 Except radon which is a radioactive element, all other noble gates occur in the elemental state in the atmosphere,Their total percentage in dry air is about `1%` by volume of which `Ar` is the major components. |
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| 386. |
Which of the following is a nitric acid anhydride?A. `N_(2)O_(3)`B. `NO_(2)`C. `N_(2)O_(5)`D. `NO` |
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Answer» Correct Answer - 3 `N_(2)O_(5)` is an acidic oxide which reacts with water with hissing sound forming nitric acid. `N_(2)O_(5)+H_(2)O rarr 2HNO_(3)` On account of this it is known as nitric anhydride. |
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| 387. |
it is possible to obtain oxygen from air by fractional distillation becauseA. oxygen is more reactive than nitrogenB. oxygen has higher boiling point the nitrogenC. oxygen has lower density than nitrogenD. oxygen is in a different group of the periodic table form nitrogen |
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Answer» Correct Answer - 2 The most economical method for commercial preparation of `O_(2)` involves liquefaction of air (after removing `CO_(2)` and water vapour) followed by fractional distillation of the liquids air so obtained. During the process ,dinitrogen `(N_(2))` with lower baking point `(77 K)` distils over in the gaseous form leaving behind dioxygen with higher boiling point `(90 K)` in the liquid state. |
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| 388. |
Anamolous behaviour of fluorine in group 17 is due toA. Small sizeB. High electronegativityC. Low F-F bond dissociation enthalpy and absence of vacant d orbitalD. All of these |
| Answer» Correct Answer - D | |
| 389. |
Which of the following form `SiO_(2)` is used in modern radio and television broadcasting and mobile radio communications?A. QuartzB. Silica gelC. KieselghurD. None of these |
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Answer» Correct Answer - A Its ability to control radio frequencies is utilized in the construction of electronic equipment, i.e., radar devices. It is also used in the construction of special lenses and prisms since it is transparent to both infrared and ultraviolet radiations. |
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| 390. |
In which of the following properties does white phosphorus resemble red phosphorus?A. Reaction with hot `NaOH` soln.B. PhosphorescenceC. Solubitlity in organic solventsD. Burning of air |
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Answer» Correct Answer - 4 Both white and red burn in excess of oxygen to from tetraphosphorus decaoxide: `P_(4)(s)+5O_(2)(g) rarr P_(4)O_(10)(s)` White `P` ignites in air at `35^(@)C` while red `P` ignites in air at `260^(@)C`. White `P`, has much lower melting and boiling points than red `P` , because very litter energy is required to sever the weak dispersion forces between the individual `P_(4)` molecules in the former allotrope. Similary white `P` , unlike red `P` , is easily dispersed as in carbon disulphide, butthis solvent is ineffecuture in breaking down the strong macromolecular structure of red `P`. White `P` is less dence than the red variety because its structure is less compact. The more open structure of the white from also accounts for its high chemical reactivity, which is further enhanced by the fact that considerable strain is present in the `P_(4)` units which is relieved by chemical reactions. While `P` dissolves in boiling `NaOH` solution in an inert atmosphere giving `PH_(3)` `P_(4)+3NaOH+3H_(2)O rarr PH_(3)+3NaH_(2)PO_(2)` Red `P` shows no sign of reaction ,White `P` glows in dark (chemilluminescemce or phosphorescence) due to slow combustion while red `P` does not glow. |
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| 391. |
which of the following element of Group `17` shows radio-activity?A. AstatineB. IodineC. BromineD. Chlorine |
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Answer» Correct Answer - 1 Astiatine does not occur in nature ,But overtwenty artificial isotopes have been made.All of these are radiancetive,The most stable isotopes are `.^(210)At (t_(1//2)=8.3" hours")` and `.^(211)At (t_(1//2)=7.5" hours")`. The latter was first made in `1940` by a nuclear reaction in which `Bi` was bombarded with high energy `alpha` prticles: `._(83)^(209)Bi+._(2)^(4) He rarr ._(85)^(211)At+2_(0)^(1)H` Tracer methods were used to study the chemistry of `.^(211)At`, using minute quantities of about `10^(-14)` mole. This isotope decays by orbital element capture and by `alpha -`emission. At appears to resmble `I` quite closely. |
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| 392. |
Identify the group 15 elements (s) which correspond to the following description. (a) exists mainly in `+3` oxidation state. (b) is a gas at room temperature (c ) forms a basic oxide (d) is the most abundant element in the atmosphere. |
| Answer» (a) Bi (b) N (c )Bi (d) N. | |
| 393. |
Which of the following is a reducing agent?A. `SeO_(2)`B. `TeO_(2)`C. `SO_(2)`D. `PoO_(2)` |
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Answer» Correct Answer - 3 Sulpher dioxides is one of the few common gases that is a reducing agent ,itself being easily oxidized to the sulphate ion: `SO_(2)(aq.)+2H_(2)O(l)rarrSO_(4)^(2-) (aq.) +4H^(+) (aq.)+2e^(-)` To test for reducing gases,such as sulphur dioxide ,we can use an oxidizing agent that undergoes a colour change, the most convenient one being the dichromate ion. A filter paper soaked in acidified orange dichromate ion will turn green as a result of the formation of the chlormium (III) ion: `Cr_(2)O_(7)^(2-)(aq.)+14H^(+)(aq.)+6e^(-) rarr 2Cr^(3+)(aq.) +7H_(2)O(l)` |
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| 394. |
In which of the following pairs of halgens do the members resemble each other more closely in their properties?A. `Cl` and `I`B. `CI` and `Br`C. `Br` and `At`D. `F` and `CI` |
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Answer» Correct Answer - 2 Because they have little difference in polarity of their bond with a given element. |
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| 395. |
The main source of fluorine is the mineralA. `Na_(2)AIF_(6)`B. `CaF_(2).3Ca_(3)(PO_(4))_(2)`C. `CaF_(2)`D. `NaF` |
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Answer» Correct Answer - 3 Halogens are very reactive elements and hence do not occur in the free elemental state in nature. They are found mainly in the form of metal halides although iodine also occurs as iodate `(IO_(3)^(-))`. The most important naturally occuring compound of fluorine is fluorspar (calcium fluoride), `Ca^(+)(F^(-))_(2)`. Other well known `F` containing minerals are fluora aptite `[3Ca_(3)(PO_(4))_(2).CaF_(2)]` and cryloite ,`(Na^(+))_(3)AlF_(6)^(3-)`,which is importance in the extraction of `Al`. |
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| 396. |
Producer gas is a mixture ofA. `CO+H_(2)`B. `CO_(2)+H_(2)`C. `CO+N_(2)`D. `CO_(2)+N_(2)` |
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Answer» Correct Answer - C A mixture of `25% CO` and `70% N_(2)` is called producer gas. The rest is `4% CO_(2)` with traces of `CH_(4), H_(2)`, and `O_(2)`. |
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| 397. |
Sulphur dioxide is a`//`an `"_____"` oxide.A. amphotericB. acidicC. basicD. neutral |
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Answer» Correct Answer - 2 The common oxide of sulpher ,sulpher dioxide, is a colourless ,dense,poisonous (toxic) gas, with a very pungent smell .It has an acid "taste ". The taste is a result of the reaction of `SO_(2)` with water on the tongue to give the weak acid sulphurous acid: `SO_(2)(g)+H_(2)O(l) hArr H_(2)SO_(3)(aq.)` The maximum tolerable levels for humans is about `5p p m` but plans begin to suffer in concentration as low as `1 p p m`. |
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| 398. |
Fluorine is prepared by the electrolysis ofA. molten cryoliteB. fused `KF`C. anhydrous `HF`D. a solution of `KHF_(2)` in `HF` |
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Answer» Correct Answer - 4 Difluorine is still produced by the Moissan electrochemical method,a process devised `129` years ago. Here fluorine is obtained by treating `CaF_(2)` with concentrated `H_(2)SO_(4)` to give an aqueous mitxture of `HF`. This is distilled yielding anhydros liquid `HF`. Then a cooled solution of `KHF_(2)` in anhydrous `HF` is electrolyzed ,giving `F_(2)` and `H_(2)`. `CaF_(2)+H_(2)SO_(4)rarrCaSO_(4)+2HF` `KF+HFrarrK[HF_(2)]` `HF+K[HF_(2)]overset("electrolyse")rarrH_(2)+F_(2)` `KHF_(2)rarrKF+HF, KF rarr K^(+)+F^(-)` Cathhode, `K^(+)+e^(-)rarrK` `K+HFrarrKF+H` `2HrarrH_(2)` Anode, `F^(-)rarrF+e^(-)` `2FrarrF_(2)` There are many differents in ibtainibng fluorine (i) `HF` is corrosive and etches glass and also causes very painful skin wounds. These arise partly by dehydraing the tissue and partly from th eacidic nature of `HF`. The wounds are slow to heal beacuse `F^(-)` ions remove `Ca^(2+)` ionsf rom the tissues (ii) Gaseous `HF` is also very toxic (`3p p m)` compared with `HCN(10p p m)` (iii) Anhydrogen `HF` is only slightly ionized and is therefore a poor conductor of electricity .Thus a mixture of `KF` and `HF` is electrolyzed to increases the conductively. Moissan used a solution of `KF` in `HF` with a mole ratio of `1:13` but modern methods use a mole ratio of `1:2` of `KF:HF` so that the vapour pressure of toxic and corrosive `HF` is much lower. this mixture melts at about `72^(@)C`, a much easier temperature to maintain .Note that `KF` and `HF` react to form the acid salt `K^(+)[F-H...F]^(-)` (iv) Water must be rigorously excluded otherwise the `F_(2)` produced will oxidize it to `O_(2)` (v) `H_(2)(g)` liberated at the cathode must be separated from the `F_(2)` liberated at the abode by a diaphragm (made of teflon), otherwise they will react explosively (vi) `F_(2)` is extermely teactiveIt catches fire with traces of grease or with crystanlline silicon. Glass and most metals are attacked. It is difficult to find suitable materials from which we could make the reaction vessel. Moissan used a Pt U- tube beause `Pt` is very unreactive but it is very expensive .`Cu` or Monel metal `(Cu/Ni" alloy")` are now used instead, because they cost less. A protective fluoride film forms on the surface of the metal and slows down further attack. (vii) The cathods are made of steel ,the anodes are carbon,and teflon is used for electrical insulation. Graphite anodes must be not be used beacuse graphite reacts with `F_(2)` froming graphite compounds `CF`. In htese `F` atoms progressively invade the space between the sheets of graphite, focusing them aprt and buckleing them. Thsi gradully stops the fraphite from conducting. Thsu current needed increase generating more heat and eventually an explosion may occur .To avoid this ungraphitized carbon is used. It is made from powered coke compacted and impregnated with `Cu`. Recently a chemical method for the prepartion of fluorine has beeen develped. This involves the following reaction: `K_(2)MnF_(6)+2SbF_(5)rarr2KSbF_(6)+MnF_(3)+(1)/(2)F_(2)` In this reaction, the stronger Lewis acid `SbF_(5)` displaces the waker one,`MnF_(5)` from its salt. `MnF_(4)` is unstable and readily decomposes to give `MnF_(3)` and fluorine. |
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| 399. |
Sulphur dioxide is produced commercially on a vast scale byA. burning sulphur in airB. buring hydrogen sulphide in airC. roasting various metal sulphidesD. All of these |
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Answer» Correct Answer - 4 `S(s)+O_(2)(g)rarrSO_(2)(g)` `2H_(2)S+3O_(2)(g)rarr2H_(2)O(l)+2SO_(2)(g)` Particularly `FeS_(2)` and to a smaller extent `CuS` and `ZnS` are roasted with air in smelters: `4FeS_(2)+11O_(2)rarr2Fe_(2)O_(3)+8SO_(2)` `2ZnS+3O_(2)rarr2ZnO+2SO_(2)` Large amounts of `SO_(2)` are produced as a waste product by burning coal and to a lesser extent, other fossile fuels, oil and gas. This undoubtedly harms the environment. In the laboratory, it is prepared by heating copper with concentrated sulphuric acid : `Cu(S)+2H_(2)SO_(4)rarrCuSO_(4)+2H_(2)O+SO_(2)uarr` Side reactions occur and asome copper sulphide is formed .The gas is dried by passing it through cone. sulphuric acid and is collected upward displacement of air. (Silver metal also undergoes similar reaction `2Ag+2H_(2)SO_(4) rarr Ag_(2)SO_(4)+2H_(2)O+SO_(2)` Alternatively, it can be made by heating a solution of a sulphite or hydrosulphite with concentrated sulphuric acid or hydrochloric acid: `NaSO_(3)+H_(2)SO_(4)rarrNa_(2)SO_(4)+H_(2)O+SO_(2)(g)` or `SO_(3)^(2-)(Aq.)+2H^(+)(aq.)rarrH_(2)O(l)+SO_(2)(g)` `NaHSO_(3)+HCl rarr NaCl +H_(2)O+SO_(2)(g)` or `HSO_(3)^(-)(aq.)+H^(+)(aq.)rarr H_(2)O(l)+SO_(2)(g)` Siphone of liquefied `SO_(2)` provide a convenient supply of the gas for laboratory use. |
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| 400. |
`CO` is commercially produced by passing steam over red hotA. charcoalB. cokeC. graphiteD. diamond |
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Answer» Correct Answer - B `C(s) + H_(2)O(g) overset(Delta)rarr CO(g) + H_(2)(g)` This reaction also produces hydrogen. |
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