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Unit 7, , p- BLOCK ELEMENTS:, 1. Classify the following 1 5 th group p-block elements in to nonmetals/metalloids, /metal., 1)Nitrogen 2) Phosphorus 3) Arsenic 4) Antimony 5) Bismuth 1M each, Answer:, Nonmetals: Nitrogen and Phosphorus, Metalloids: Arsenic and Antimony, Metal: Bismuth, 2. Write the formula of, 1M each, 1) chile salt petre 2) Indian salt petre 3)apatite mineral 4)chlorapetite 5) Fluorapetite, Answer: 1) NaNO3 2) K NO3 3) Ca9(PO4)6 CaX2, 4) Ca9(PO4)6 CaCl2, 5), Ca9(PO4)6 CaF2, 3. Write the valence shell electronic configuration of 15th group elements., 1M, Answer; ns2 np3, 4. There is a considerable increase in covalent radius from N to P. However, from As to Bi, only small increase in covalent radius is observed. Give reason., 1M, Answer: This is due to the presence of completely filled d and/or f orbital in heavier, members., 5. Ionization enthalpy decreases down the group 15. Give reason., 1M, Answer: Due to gradual increase in atomic size., 6. The ionization enthalpy of the group 15 elements is much greater than that of group, 14 and group 16 elements in the corresponding periods. Give reason., 1M, Answer: Because of the extra stable half-filled p orbital electronic configuration and smaller, size., 7. How does electronegativity of 15th group elements varies down the group?, 1M, Answer: decreases, 8. Mention the common Oxidation states of p block elements., 1M, Answer: common ox.state of these elements are-3,+3 and +5, 9. How is stability of oxidation states of 15th group elements varies?, 1M, Answer: -3 in their covalent compounds. In addition to the −3 state, N and P also show −1, and −2, All the elements present in this group show +3 and +5 oxidation states. Stability of +5 ox., State decreases and that of +3 ox. State increases due to inert pair effect.
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10.Nitrogen atom has five valence electrons but it does not form NCl5., 1M, Answer: Because of absence of d-orbitals it can’t expand its covalency from 3 to 5., 11.Nitrogen does not form pentahalides.Why?, 1M, Answer: Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to expand, its covalence beyond four. That is why it does not form pentahalide., 12.Why is Nitrogen an inert gas?, 1M, Answer: Nitrogen exists as triply bonded diatomic non polar molecule. Due to short, internuclear distance between two nitrogen atoms the N ≡ N bond strength is very high. It, is, therefore, very difficult to break the bond., 13.Why nitrogen exhibits anomalous behavior?, 2M, Answer: Due to smaller size, high electronegativity, high ionisation enthalpy and nonavailability of d-orbitals, nitrogen shows anomalous behavior., 14.Mention any three anomalous properties of nitrogen., 3M, Answer; (any three of the following), 1)Nitrogen forms pπ – pπ bonds where as other members not., 2) nitrogen exists as diatomic molecule with a triple bond, 3)The single N−N bond is weaker than P−P bond due to small bond length., 4) lower catenation tendency., 5)cannot form dπ – pπ bonds like phosphorus., 15.Why R3P=O exist but R3N=O does not?, 1M, Answer: Due to the absence of d orbitals in valence shell of nitrogen, nitrogen cannot form, d π–p π bond. Hence R3N=O does not exist., 16.Catenation property of nitrogen is less than phosphorus. Why?, 1M, Answer: Due to strong pπ–pπ overlap in Nitrogen and weaker N-N bond than the single PP bond., 17.Write the formula of hydrides formed by 15th group elements?, 1M, Answer: EH3, 18.How does the stability of 15th group metal hydride varies down the group?, 1M, Answer:The stability of hydrides decreases on moving down from NH3 to BiH3., 19.Why is NH3 basic while BiH3 is only feebly basic., 1M, Answer: NH3 is basic due to smaller size & high electro negativity of Nitrogen., 20.Ammonia has higher boiling point than Phosphine. Explain., 1M, Answer: Ammonia (NH3) form hydrogen bond but Phosphine (PH3) does not. Hence boiling, point of ammonia is higher than that of phosphene., 21.Write the formula of two types of oxides formed by 15th group elements?, 1M, Answer: E2O3 and E2O5, 22.Out of E2O3 and E2O5 which is acidic?, 1M
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33.How does dilute nitric acid with copper?, 2M, Answer: Dil. Nitric acid reacts with copper to form cupric nitrate with the liberation of, nitric oxide., 3Cu + 8 HNO3(dilute) → 3Cu(NO3)2 + 2NO + 4H2O, 34.How does concentrated nitric acid with copper?, 2M, Answer: Conc.Nitric acid reacts with copper to form cupric nitrate with the liberation of, nitrogen dioxide., Cu + 4HNO3(conc.) → Cu(NO3)2 + 2NO2 + 2H2O, 35.How does dilute nitric acid with zinc?, 2M, Answer: Dil. Nitric acid reacts with zinc to form zinc nitrate with the liberation of nitrous, oxide., 4Zn + 10HNO3(dilute) → 4 Zn (NO3)2 + 5H2O + N2O, 36.How does concentrated nitric acid with zinc?, 2M, Answer: Conc.Nitric acid reacts with zinc to form zinc nitrate with the liberation of, nitrogen dioxide., Zn + 4HNO3(conc.) → Zn (NO3)2 + 2H2O + 2NO2, 37.How does concentrated nitric acid with iodine?, 2M, Answer: Conc.Nitric acid oxidizes iodine to form iodic acid., I2 + 10HNO3 → 2HIO3 + 10NO2 + 4H2O, 38.How does concentrated nitric acid with carbon?, 2M, Answer:, Conc.Nitric acid oxidizes carbon to carbon dioxide, C + 4HNO3 → CO2 + 2H2O + 4NO2, 39.What is passivity?, 1M, Answer: Some metals like aluminium and chromium do not dissolve in concentrated, nitric acid due to the formation of a protective layer of oxide on the surface of the, metal. This phenomena is called passivity of metals., 40.explain Brown ring test with equations ., 3M, Answer:, Dilute FeSO4 solution is added to an aqueous solution of nitrate ion., concentrated H2SO4 is then added along the sides of the test tube. A brown ring is, observed at the interface between the solution and H2SO4 layers indicates the presence of, nitrate ion in the solution., NO3- + 3Fe2+ + 4H+ → NO + 3Fe3+ + 2H2O, [Fe (H2O)6 ]2+ + NO → [Fe (H2O)5 (NO)]2++ H2O, (brown), 41.Write the resonance structurs of a) NO b) NO2 c) N2O5, 1M each, Answer:
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a) Structure of NO:, , b) Structure of NO2 :, , c) Structure of N2O5 :, , 42.Distinguish between white and red phosphorus., Answer: (any two), White phosphorus, It is a soft and waxy solid., It is poisonous., It is insoluble in water but soluble in, carbon disulphide., Highly reactive, In both solid and vapour states, it exists as, a P4 molecule., Less stable, , 2M, , Red Phosphorus, It is a hard and crystalline solid., It is non-poisonous., It is insoluble in both water and carbon, disulphide., It is relatively less reactive., It exists as a chain of tetrahedral P4 units., More stable, , 43.How is Phosphine prepared in the laboratory form white phosphorous?, 2M, Answer: In the laboratory phosphene is prepared by heating white phosphorus with, concentrated NaOH solution in an inert atmosphere of CO2., P4 + 3NaOH + 3H2O → PH3 + 3NaH2 PO2, 44.Give a reaction to support Basic nature of phosphine., 2M, Answer: Phosphine react with hydrogen bromide and forms phosphonium bromide., PH3 + HBr → PH4 Br, 45.How is Phosphorous trichloride is obtained from phosphorous and chlorine? 2M, Answer: Phosphorus tri chloride is obtained by passing dry chlorine over heated white, phosphorus., P4 + 6Cl2 → 4PCl3, 46.How is Phosphorous pentachloride is obtained from phosphorous and chlorine? 2M
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51.Write the formula, structure ,reducing property and basicity of Orthophosphoric acid., 3M, Answer:, Formula- H3PO4, Reducing property: Not a Reducing agent as it does not have P – H linkage, structure:, , Basicity: Three( as it contains three P-OH linkage), 52.How do you account for the reducing behavior of H3PO2 on the basis of its structure?, 1M, Answer: In H3PO2, two H atoms are bonded directly to P atom which imparts reducing, character to the acid., 53.Classify the following 1 6 th group p-block elements in to nonmetals/metalloids /, metal., 1)Oxygen 2) Sulphur 3) selenium 4) Tellurium 5) Polonium, 1M each, Answer:, Nonmetals: Oxygen and Sulphur, Metalloids: selenium and Tellurium, Metal: Polonium, 54.Name the 16th group p-block element which is radioactive in nature., 1M, Answer: Polonium, 55.Write the valence shell electronic configuration of 16th group elements., 1M, Answer; ns2 np4, 56.Mention the Oxidation state of oxygen., 1M, Answer; Oxygen exhibits the oxidation state of−2 in metal oxides, −1 (H2O2), zero (O2 and, O3) and +2 (OF2)., 57.Write a note on Anomalous Behavior of Oxygen., 3M, It is due to its Small size, High electronegativity and absence of d-orbitals oxygen shows, anomalous properties., 1. Strong hydrogen bonding is present in H2O, which is not found in H2S., 2. Absence of d-orbitals in oxygen limits its covalence to four and in practice rarely, exceeds two. On the other hand, other elements of the group can expand their, covalence beyond four.
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58.How is Oxygen obtained from potassium chlorate?, Oxygen can be obtained by heating potassium chlorate in presence of MnO2., , 2M, , 59.Write the chemical equation for the reaction of Oxygen with aluminum /carbon, /methane., 1M each, Answer:, , 60.What are acidic oxides? What type of oxides are acidic in nature? Give example. 3M, Answer: Acidic oxides are those oxides which combine with water to give an acid., Non-metal oxides and Oxides of some metals in higher oxidation state are acidic in nature., Example for non metal acidic oxides− SO2, Cl2O7, CO2, N2O5, Examples for metal oxides which are acidic − Mn2O7, CrO3, V2O5, 61.What are basic oxides? What type of oxides are basic in nature? Give example. 3M, Answer: Basic oxides are those oxides which combine with water to give bases., Metal oxides are basic in nature., Examples for metal oxides which are basic- Na2O, CaO, BaO, 62.What are amphoteric oxides? Give example., 2M, Answer: Amphoteric oxides are those oxides which show the characteristics of both acidic, as well as basic oxides ., Example − Al2O3, 63.Illustrate amphoteric nature of Al2O3 with suitable reactions., 2M, Answer:, , 64.What are neutral oxides? Give example., 2M, Answer: Neutral oxides arethose oxides which are neither acidic nor basic., Examples − CO, NO, N2O, 65.How is Ozone prepared from oxygen?, 2M, Answer: A slow dry stream of oxygen is passed through a silent electrical discharge. Oxygen, partially gets converted into ozone., 66.Why is high concentrations of ozone can be explosive?, 2M, Answer: High concentrations of ozone can be explosive because the decomposition of O3 to, O2 results in the liberation of heat (ΔH = − ve) and an increase in entropy (ΔS = + ve), leading, to large negative value of ΔG.
