ICSE QUESTION PAPER Class X Chemistry (2016) Solution

Transcription

1 ICSE QUESTION PAPER Class X Chemistry (016) Solution Section I 1. Metals are good reducing agents because they are electron donors. Electrovalent compounds have high melting points. (iii) Higher the ph value of solution, the more alkaline it is. (iv) AgCl, a white precipitate, is soluble in excess NH 4 OH. (v) Conversion of ethene to ethane is an example of hydrogenation. (A) 17 Element with atomic number 19 will lose 1 electron to achieve the noble gas configuration which can be accepted by element with atomic number 17. (C) 1:1 1 mole of hydrogen 1 g of hydrogen 1 mole of hydrogen molecules 1 g of hydrogen molecules g of hydrogen molecules 1 mole of oxygen 16 g of oxygen 1 mole of oxygen molecules 16 g of oxygen molecules 3 g of oxygen molecules (iii) (D) Copper and tin Bronze is an alloy which consists of copper and tin. (iv) (B) mainly ions Strong electrolytes dissociate into ions. (v) (C) HCl is highly soluble in water. HCl is highly soluble in water. Its high solubility may be demonstrated by the fountain experiment.

2 AlN (s) + 3H O (l) Al(OH) 3(aq) + NH 3(g) Cu (s) + 4HNO 3(aq) Cu(NO 3 ) (aq) + NO (g) +H O (l) (iii) NaHCO 3(s) + HCl (l) NaCl (aq) + H O (l) + CO (g) (iv) Na SO 3(s) + H SO 4(l) Na SO 4(aq) + H O (l) + SO (g) (v) CH 3 CH Cl + KOH (aq) CH 3 CH OH + KCl (aq) When dil. HCl is added to lead nitrate solution and heated, it forms a white precipitate of lead chloride. Pb(NO 3 ) + HCl PbCl + HNO 3 A white precipitate of barium sulphate forms when barium chloride is mixed with sodium sulphate. BaCl (aq) + Na SO 4(s) NaCl (aq) + BaSO 4(s) (iii) When sugar reacts with conc. H SO 4, it gives a black spongy mass of carbon which is called sugar charcoal. Conc. HSO 4 C1 H O11 s 1C(s) 11HO (iv) When dilute hydrochloric acid is added to copper carbonate, it decomposes to give copper chloride. CuCO 3 + HCl CuCl + H O + CO (v) Dil. HCl reacts with thiosulphates to produce sulphur dioxide and yellow sulphur is precipitated. Na S O 3 + HCl NaCl + H O + SO + S (e) The tendency of an atom to attract electrons to itself when combined in a compound: Electronegativity The method used to separate ore from gangue by preferential wetting: Froth flotation process (iii) The catalyst used in the conversion of ethyne to ethane: Lindlar catalyst (iv) The type of reactions alkenes undergo: Addition reaction (v) The electrons present in the outermost shell of an atom: Valence electrons

3 (f) Given : Mass of gas 3 g Volume occupied by 3 gms of gas 0 litres volume of gas 0 Number of moles of gas molar gas volume.4 Mass of gas Number of moles of gas Gram molecular weight of gas Gram molecular weight of gas Mass of gas 3 Number of moles of gas g Ca(NO ) CaO 4NO O 3 At STP, 1 mole of any gas contains.4l Sin ce, 4 moles of NO are produced, volume of nitrogen dioxide obtained L (g) moles of Ca(NO ) produces moles of CaO g Ca(NO ) produces 11 g CaO 1 g Ca(NO 11 ) will produce g CaO g CaO Hence, 8 g of Ca(NO ) will produce g of CaO Column-I Pb(NO 3 ) from PbO MgCl from Mg FeCl 3 from Fe NaNO 3 from NaOH ZnCO 3 from ZnSO 4 3 Column-II Precipitation Simple displacement Combination Neutralisation Titration (h) 1. 1-Propene. -Butyne 3. Ethanal 1. less than. less than

4 . 5 Atom J is a Group 5 element and a group is determined by the number of electrons present in the outermost shell. Element M from Group 7 accepts one electron to form an ion with a single negative charge. (iii) T is more reactive than R. The tendency of losing electrons increases down the group. Because chemical reactivity depends on the tendency to lose electrons, thus reactivity increases on going down the group. (iv) Element T has its electrons arranged in four shells. Element T belongs to Period 4, and all elements of this period have four shells. Metallic Smallest (1) Ionic bond is formed by transfer of one electron from element W to element X. () Covalent bond is formed by sharing of electrons between elements Y and Z. (1) HCl () NaCl 3. CH 6 7O 4CO 6H O CaC H O Ca(OH) CH Conc.H SO 4/170 C (iii) C H OH CH CH H O 5

5 (iii) CH CH When bromine dissolved in CCl 4 is added to ethene, the orange colour of bromine disappears because of the formation of colourless ethylene bromide. Nitric oxide Nitrogen dioxide 4. Sulphur dioxide Freshly prepared K Cr O 7 paper changes from orange to green. Hydrogen sulphide The gas released has a rotten egg smell. When NH 4 OH is added to copper sulphate solution drop-wise, a pale blue ppt. is obtained. CuSO 4 NH 4OH Cu(OH) (NH 4) SO4 With excess of NH 4 OH, the ppt. dissolves to give a deep blue solution of tetrammine copper(ii)sulphate. Cu(OH) (NH 4) SO4 NH 4OH [Cu(NH 3) 4]SO 4 4H O When NH 4 OH is added to zinc sulphate solution drop-wise, a white, gelatinous ppt. is obtained. ZnSO 4 NH 4OH Zn(OH) (NH 4) SO4 With excess of NH 4 OH, the ppt. dissolves to give a colourless solution of tetrammine zinc(ii)sulphate. Zn(OH) (NH 4) SO4 NH 4OH [Zn(NH 3) 4]SO 4 4H O

6 Electrodes: Cathode: Copper Anode: Platinum Reaction at the cathode: Cu + + e Cu Reaction at the anode: 4OH - 4e 4OH OH + OH H O + O The cathode and anode are both made of graphite plates. Reaction at the cathode: Pb + + e Pb Reaction at the anode: Br - e Br Br + Br Br Oxygen is the product formed at the anode. Ag + and Na mole oxygen molecule x moles of oxygen molecule 1 10 molecules molecules moles of oxygen molecule 1 10 molecules Number moles of O molecul Mass of O Molar mass of O Mass of O g es occupies.4l molecules occupies L volume Vapour density = 9 Element Percentage At. mass Gram atom Ration Carbon /1 = /6.9 = 1 Hydrogen /1 = /6.9 =.5 5 Empirical formula is C H 5 Molecular weight = Vapour density Molecular weight = n (Empirical formula weight) 58 = n ( ) n = So, molecular formula = C 4 H 10

7 4NH 5O 4NO 6H O 3 4 moles of ammonia 100 cm 1 mole of ammonia 5 cm 4 moles of ammonia requires 5 moles of O. So, volume of oxygen required cm Ammonia Nitrogen 8NH 3 + 3Cl N + 6NH 4 Cl 3PbO + NH 3 3Pb + 3H O + N B A (iii) C Electrostatic forces of attraction between ions in the solid state are very strong. These forces weaken in the fused state or in the solution state. Hence, ions become mobile. If silver nitrate solution is used directly instead of double cyanide of silver and sodium, the deposition of silver will be very fast and hence not very smooth and uniform. (iii) Copper has no mobile electrons in the solid state and an electrolyte should dissociate into oppositely charged ions to conduct electricity. Hence, copper is a non-electrolyte.

8 7. Conc. caustic soda Heat Al(OH) Al O 3H O C 3 (iii) Cryolite (iv) At the cathode: Al e Al (v) The anode has got to be replaced from time to time as it gets oxidised by the oxygen evolved at the anode. When exposed to the atmosphere, it becomes a monohydrate. Na CO.10H O Na CO.H O 9H O Dryair 3 3 It absorbs moisture from the atmosphere to become moist and ultimately dissolves in the absorbed water, forming a saturated solution. Fe 3+ ion FeCl 3NaOH Fe(OH) 3NaCl Pb + ion 3 3 (Re ddish brown ppt.) Pb(NO ) NH OH Pb(OH) NH NO (iii) Ca + ion Ca(NO ) NaOH Ca(OH) NaNO 3 3 (chalky whiteppt. insolublein excess) (White ppt.sparingly soluble)