2024 Prelims RVHS H2 Chem P2 (Ans)

1 River Valley High School 2024 JC2 H2 Chemistry 9729 Prelim Exam Paper 2 Suggested Solutions 1 (a) (i) Proton and deuterons are deflected to the negative plate , but hydrogen atoms is not deflected . This is because protons and deuterons are positively charged , whereas hydrogen atoms are electrically neutral. The mass of a proton is half of the mass of a deuteron (1 neutron and 1 proton), thus angle of deflection for proton doubled to that of deuterons. [2] (ii) +1310 kJ mol−1 (Same value as first IE for hydrogen.) The electron to be removed from deuterium atom and hydrogen atom experience the same nuclear charge and no shielding effect. They are of similar/same distance from the nucleus . Thus, the attraction of positive nucleus for the (1s) electrons to be removed is the same. Or Hydrogen and deuterium have the same electronic configuration . Although deuterium has an additional neutron , it has no charge , therefore does not affect the attraction of nucleus for the electrons to be removed. [2] (b) (i) 1s2 2s2 2p6 3s2 3p6 3d8 4s2

2 (ii) For all atoms, there is an increase in successive ionisation energies as the electron is removed from an ion of increasing positive charge. The significant jump from 2 nd to the 3rd ionisation energy for element A is due the removal of the 3 rd/3p electron from an inner principal quantum shell which is more strongly attracted to the positive nucleus compared to a 3s electron. 3d and 4s electrons are very close in energy. Similar amount of energy is required to remove the 4s/2nd and 3d/3rd electron from Ni. (iii) Element B is Mg. [1] (c) (i) 2NO + 2CO → N2 + 2CO2 Or NO2 + 2CO → ½ N2 + 2CO2 [1] (ii) During adsorption, the formation of weak bonds between the NO x molecules and the active sites on rhodium surface weakens/breaks the bonds within the NOx molecules. Reaction occurs more readily as the NO x particles are held on rhodium surface in close proximity and in the correct orientation. During desorption, the weak bonds between the product particles and the rhodium surface are broken . The products formed diffuse away from the surface of the catalyst and the active sites become available again. [3] (d) (i) First order with respect to CxHy at low concentration, but zeroth order at high concentration. At high [C xHy], adding more substrates cannot accelerate the reaction as all the active sites on the catalyst surface are saturated/ occupied. [2] (ii) [2]

3 A catalyst provides an alternative reaction pathway with a lower activation energy . As a result, more reactant particles possess energy  activation energy required for an effective collision and the frequency of effective collisions increases . Thus, rate constant is increased. (iii) (e) NO2 forms photochemical smog which causes respiratory problems. [1] 2 (a) (i) A B [2] (ii) Condensation/ Addition-elimination [1]