EJC Prelim P1_Worked_Solution

2018 JC2 Preliminary Examination H2 Chemistry 9729 Paper 1 Worked Solution 1 The positive α particles either passes straight through the empty space or are occasionally repelled by the dense positive nucleus. They are not affected by the much smaller electrons and hence does not provide any information about the electrons.  C 2 [O] : 2Am Amnn ne++ −→+ [R] : 32Cu Cunn e n+− ++→ So, 32 2Am Cu Am Cunn nn++ +++→+ 4 Am 25.0 0.0100 2.5 10 mol1000 nn + −=× = × 3 4 Cu 15.0 0.0500 7.5 10 mol1000n + −=× = × CuAm :1 : 1 : 3 3nnn n n+ ==  = Am species formed has O.S. of +6 () 2 2AmO +  D 3 OF 2 : 2 b.p. + 2 l.p.  bent  105º CH4 : 4 b.p. + 0 l.p.  tetrahedral  109.5º SF6 : 6 b.p. + 0 l.p.  octahedral  90º H2O : 2 b.p. + 2 l.p.  bent  105º O3 :  bent  <120º N2O :  linear  180º PF3 : 3 b.p. + 1 l.p.  trig. pyr.  107º BF3 : 3 b.p. + 0 l.p.  trig. planar  120º IF3 :  trig. planar  120º NO2 :  bent  >120º SO2 : 2 b.p. + 1 l.p.  bent  <120º CO2 : 2 b.p. + 0 1.p.  linear  180º  B 4 Bonding in solid NH 4HF2:  A 5 At low pressure, gas particles are far apart. IMF between particles causes force they impinge on wall to be smaller and thus pressure is lower than ideal gas  pVreal < pVideal At higher pressure, gas particles are close together and the volume occupied by particles is significant compared to volume of container. Hence the gas occupies a larger volume than ideal gas  pVreal > pVideal  B 6  Arrhenius acid: Produces H+(aq) in water  Brønsted-Lowry acid: H+ donor; B(OH)3 accepts a OH– and does not donate H+  Lewis acid: Lone pair acceptor; accepts a lone pair fron OH–  Monobasic acid: each mole of B(OH)3 reacts with one mole of OH–  B 7 NaC l : no hydrolysis  pH = 7 MgCl2 : slight hydrolysis  pH ≈ 6.5 22MgC H O Mg(OH)C HC++ll l … AlCl3 : extensive hydrolysis  pH ≈ 3 32 3A C 3H O A (OH) 3HC+→ +ll l l SiCl4 : complete hydrolysis  pH ≈ 1 42 2SiC 2H O SiO 4HC+→ +ll PCl5 : complete hydrolysis  pH ≈ 1 52 3 4PC 4H O H PO 5HC+→ +ll  A 8 A : Graph is for ionic radii B : Melting point of Si should be highest due to extensive strong Si–Si covalent bonds within giant molecular structure C : Nuclear charge increases across period while shielding effect is the same, hence ENC increases across the period resulting in increase in electronegativity D : Silicon being a metalloid should only have conductivity below that of the metals (Na, Mg, Al)  C 9 () () ()() ()() ()() ()() ()() ()() ()() ()() 1f f ff 2 ff 2 f f2 ff 2 products reactants 2N a O H a q H g 2N a s 2H O 2N a O H a q 0 02 H O 2N a O H a q 2H O HH H HH HH H H HH Δ= Δ − Δ =Δ + Δ − Δ− Δ =Δ + − −Δ =Δ −Δ   l l l dd d dd dd d d dd ()() ()()f2 c 2HO H gHHΔ= Δ ldd as both corresponds to the same reaction: H2(g) + ½O2(g) → H2O(l)  B 10 B : At 298 K, C is a solid C : Hydrogen exists as H 2 under std state D 