2025 H2 Chem Prelim P1 detailed ans_VJC

1 VICTORIA JUNIOR COLLEGE 2025 JC2 H2 CHEMISTRY PRELIM EXAM PAPER 1 ANSWERS 1 B 7 D 13 C 19 C 25 D 2 A 8 A 14 D 20 D 26 B 3 C 9 A 15 B 21 C 27 C 4 D 10 B 16 A 22 C 28 B 5 B 11 A 17 D 23 A 29 A 6 B 12 C 18 D 24 A 30 D 1 B species Bk2+ Fm3+ protons 97 100 neutrons 249 – 97 = 152 252 – 100 = 152 electrons 97 – 2 = 95 100 – 3 = 97 Hence, Fm3+ has more electrons than Bk2+ but both ions have the same number of neutrons 2 A According to Hund’s rule, electrons will occupy the subshells singly first before pairing up. All the elements in Period 3 have principal quantum 3 as its valence shell. There is 1 orbital for s subshell and 3 orbitals for p subshell. element electronic configuration no. of paired electrons Na [Ne]3s1 0 Mg [Ne]3s2 2 Al [Ne]3s23p1 2 Si [Ne]3s23p2 2 P [Ne]3s23p3 2 S [Ne]3s23p4 4 Cl [Ne]3s23p5 6 Ar [Ne]3s23p6 8 Total no. of paired electrons = 0 + 2 + 2 + 2 + 2 + 4 + 6 + 8 = 26 3 C All three molecules have instantaneous dipole -induced dipole and permanent dipole -permanent dipole interactions. Statement 1 (incorrect): Chlorine is more electronegative than bromine and thus there is a larger electronegativity difference between hydrogen and chlorine than between hydrogen and bromine. Correspondingly, there is a larger overall dipole moment in HC l, which leads to stronger permanent dipole - permanent dipole interactions between molecules of HCl than between molecules of HBr. Statement 2 (correct): Fluorine has less electrons than bromine. Thus, the total number of electrons in HF is less than that in HBr. This leads to HF having a smaller electron cloud size and less extent of electron cloud polarisation, resulting in weaker instantaneous dipole - induced dipole interactions between HF molecules. Statement 3 (Correct): Fluorine is more electronegative than chlorine and thus there is a larger electronegativity difference between hydrogen and fluorine than between hydrogen and chlorine. Correspondingly, there is a larger overall dipole moment in HF, which leads to stronger permanent dipole -permanent dipole interactions between molecules of HF than between molecules of HCl. 4 D 5 B Option A (incorrect): Only molecules of ideal gases are assumed to have elastic collisions i.e. collisions are associated with no loss of kinetic energy. Option B (correct): Molecules of both ideal gases and real gases are in constant random motion. Option C (incorrect): Only molecules of ideal gases are assumed to have no intermolecular forces of attraction. Option D (incorrect): Molecules of ideal gases only are assumed to have negligible volume (size) compared to the volume (size) of the container. 6 B Option A (incorrect): A compound containing a hydrogen atom is not necessarily an Arrhenius acid. Option B (correct): As acetylene is unable to react with water, it is unable to dissociate in water to form H 3O+, which is characteristic of an Arrhe