MAHESH TUTORIALS I.C.S.E.

Transcription

1 ICSE X MAHESH TUTRIALS I.C.S.E. Marks : 80 Exam No. : MT/ICSE/I SPA 033SUBJECT : CHEMISTRY Time : 2 hrs. Sulphuric acid, Ammonia, Analytical Chemistry, rganic Chemistry HCl, Nitric acid, Metallurgy Model Answer Paper A.. SECTIN I (40 Marks) Attempt all questions from this section. (A). (A) an alkane 2. (D) Copper [II] oxide 3. (B) S 4. (B) Ammonium nitrite 5. (C) Eight (B). Catalytic hydrogenation 2. Methane 3. Esterification reaction /Dehydration 4. Catenation 5. Dehydrohalogenation (C). E : Ag(NH 3 Cl 2. B : AgCl 3. D : FeCl 2 4. A : NH 4 Cl 5. C : PbCl 2 (D). 2CH 4 500ºC electric arc HC CH + 3H 2 ethyne 2. H C C H Ni 300ºC H 2 C = CH 2 ethene 3. CH 3 CH + NH 4 H CH 3 CNH 4 ammonium acetate 4. CH 4 [] CH 3 H methane K 2 Cr 2 7 methanol CH 3 H [] HCH K 2 Cr 2 7 formaldelyde (E). Fe.N 2. (i) X - Fe (ii) Y - H 2 T7 I SPB 008

2 When the test tube is shaken the conc. H 2 may further mix with water. The heat evolved assists in decomposing the unstable brown ring. 4. In the brown ring test the conc. sulphuric acid being heavier settles down and the iron [II] sulphate layer remains above it resulting in formation of the brown ring at the junction. 5. N (F). 2, 2 dimethyl pentane 2. Propanoic acid Propanol Butyne 5. Pentan - 3- one (G). According to Le Chatelier s principle if a reaction proceeds with decrease in volume then the forward reaction is favoured (i.e. higher percentage yield of NH 3 by increasing the pressure. 2. Sulphuric acid is a dibasic acid. Sulphuric acid forms two types of salts with an alkali since its basicity is two. NaH NaH [insufficient] [acid salt] 2NaH Na 2 + 2H 2 [excess] [normal salt] 3. Homologous series is a series of organic compounds, where the successive members follow a regular structural pattern, successive compounds differing by a-ch 2 group. All members show similar chemical properties because of same functional group. The physical properties like boiling point, melting point, increase with increase in molecular weight. 4. Concentrated Sulphuric acid has a strong affinity towards water and hence acts as a drying agent. 5. In its aqueous solution, ammonia is present in the form of NH 4 H which dissociates partially to give NH 4 + & H ions which are responsible for conduction of electricity. (H). Solution turns pale brown. 2. A white precipitate is observed. 3. Effervescences are seen./ colourless gas is evolved. 4. Fruity smell is observed. 5. White precipitate is observed. T7 I SPB 008

3 A.2 SECTIN II (40 Marks) Attempt any four questions from this section. (A). (B) Dehydrating agent 2. (D) xidizing agent 3. (C) Non-volatile acid 4. (D) xidizing agent 5. (A) Acid (B). Fe C 2Fe + 3C 2 molten iron 2. 2Al(H) 3 00ºC Al H 2 pure alumina 3. 4Al Al 2 3 (bright light) heated alumina air (Aluminium oxide) 4. ZnC 3 < 400ºC Zn + C 2 calamine zinc carbonate 5. Cu + Zn Zn + Cu A.3 (A). Reaction with copper Cu + 4HN 3 Cu(N 3 + 2H 2 + 2N 2 When Cu is heated with conc. HN 3, reddish brown fumes of N 2 are evolved. 2. Heating Conc. HN 3 Conc. 4HN 3 2H 2 + 4N Reddish brown fumes of N 2 evolved N 2 is acidic moist blue litmus turns red. 3. Brown Ring Test for detection of Nitrate Radical: i) Take dilute HN 3 at room temperature. ii) Add freshly prepared saturated ferrous sulphate solution. iii) Then add conc. H 2 from the sides of the test tube slowly. iv) A brown ring of nitroso ferrous sulphate is obtained at the junction of the two liquids. 6Fe + 3H 2 + 2HN 3 2Fe 2 ( ) 3 + 4H 2 + 2N (conc.) (dil.) Fe + N Fe.N Nitroso Iron (II) Sulphate 5 T7 I SPB 008

4 (B). 2Al + 2NaH + 2H 2 2NaAl 2 + 3H 2 Sodium aluminate 2. Zn + 2NaH Na 2 Zn 2 sodium zincate (C). Ethyl alcohol containing pyridine or copper sulphate is termed as denaturated alcohol. 2. Anhydrous acetic acid on cooling below 6.5ºC crystallizes out in the pure form, forming a crystalline mass resembling ice. Hence pure acetic acid is called glacial acetic acid. 3. Esterification is a condensation of an alcohol with an acid in the presence of dehydrating agent [conc. H 2 ] to give an ester. A.4 (A). Aluminium is above copper in the reactivity series, it forms stronger oxides as compared to copper, hence copper oxide can be reduced using carbon but aluminium oxide cannot be reduced. ½ 2. Aluminium is an amphoteric metal it would react with the alkalis present in the cleaning powder to form a soluble salt and hence would corrode. ½ (B). C 3 H 6, C 2 H Nickel / Platinum (C). Tap water contains chlorine. This forms dil. hydrochloric acid, which will form a white ppt. with AgN 3 soln. Hence tap water is not used. 2. HCl acid is used to clean metal surfaces (pickling) before galvanizing as it removes oxide layer formed over the metal. 3. H + ions formed on ionisation of hydrogen chloride gas results in its acidic property. The ionisation occurs in the presence of a polar covalent solvent such as water. Hence, dry HCl gas does not affect a dry strip of blue litmus paper but it turns red in the presence of water. 4. Due to the high solubility of HCl gas in water, it fumes in moist air forming tiny droplets of hydrochloric acid. A.5 (A). Bayer s process is the process for concentration of Bauxite ore. The impure bauxite is purified to pure aluminium through different steps. 2. Red mud is the insoluble impurity such as iron (III) oxide etc. left behind on treating the ore with sodium hydroxide or caustic soda. The impurities are removed by dissolving the ore in sodium hydroxide followed by filtration. T7 I SPB 008

5 Sodium hydroxide is used for concentration of bauxite. Bauxite is digested with conc. soln. of NaH under pressure. Being amphoteric, it reacts with NaH forming salt and H 2. Moreover the impurities present (Fe 2 3 and Si 2 ) in bauxite remain unaffected with conc. alkali soln. Hence it is used to remove impurities in bauxite ore. (B). Sulphite or pyrite burners. S + 2 S 2 4 FeS Fe S 2 2. Contact tower 2S (air) V ºC - 2 atmos. 2S Absoption tower S 3 H 2 S Dilution tank H 2 2H 2 (C) A :- Sodium chloride (NaCl) B :- Conc. Sulphuric acid. C :- Lead chloride (PbCl 2 ) A.6 (A). H C C H Ni 300ºC H C C H Ethyne H H Ethene 2. H - C C H + 2CuCl + 2NH 4 H Cu C C - Cu + 2NH 4 Cl + 2H 2 Ethyne Copper acetylide (Red precipitate) 3. CH 3 I + 2[H] Zn/ Cu couple Alcohol CH 4 + HI Iodomethane Nascent hydrogen Methane 4. C 2 H 5 H + conc.h 2 70ºC CH 2 = CH 2 Ethene T7 I SPB 008

6 (B). Ammonia gas is collected by the downward displacement of air. 2. A glass rod dipped in conc. HCl acid is brought near the mouth of the jar. Dense white fumes of ammonium chloride are formed. 3. Fountain experiment 4. If ammonia is inhaled it affects the respiratory system. (C). The organic acid present in vinegar is acetic acid. 2. Bromo ethane reacts with alcoholic KH to liberate ethene by dehydro halogenation. A.7 (A). Hall Heroult s process. 2. Aluminium is amongst the highly reactive metals in the acitivity series, it forms strong oxides which are difficult to be reduced to metal. Hence, electrolytic reduction is done to obtain aluminium from alumina. 3. Cryolite : Na 3 AlF 6 3Na + + Al F Fluorspar : CaF 2 Ca F Alumina : Al 2 3 2Al Cathode : Carbon lining of the cell. Anode : Thick carbon rods. (B). H CH 3 C CH 2 2. H 3 C CH CH 3 CH 3 (C). Sodium hydroxide solution when added to zinc sulphate solution, a gelatinuous white precipitate is formed, which is soluble in excess of sodium hydroxide solution. Zn + 2NaH Na 2 + Zn(H Zn(H + 2NaH(excess) Na 2 Zn 2 + 2H 2 sodium zincate (colourless soln. 2. Cu + NH 4 H (NH 4 + Cu(H blue Copper (II) hydroxide (pale blue) T7 I SPB 008 Ppt is soluble in excess of NH 4 H Cu(H + (NH 4 + 2NH 4 H 4H 2 + [Cu(NH 3 ) 4 ] (in excess) Tetramine copper (II) sulphate (Deep blue solution) r Cu(H + 4NH 4 H 4H 2 + [Cu(NH 3 ) 4 ] (H Tetramine copper (II) hydroxide Deep blue solution 2