XMS 2026 Sec 3 Pure Chemistry WA1 Mark Scheme

Marking Scheme 3E Chemistry WA 1 2026 Section A – MCQ 1 2 3 4 5 A D A C D Section B – Structured Questions Qn Marking Scheme Marks 6a experiment gas 1 gas 2 water level at U increases remains the same decreases 1 carbon dioxide (CO2) propane (C3H8)  2 carbon dioxide (CO2) ammonia (NH3)  1 1 6b 1. Nitrogen has a relative molecular mass of 28, which is lower than that of carbon dioxide, which has a relative molecular mass of 44, but higher than that of ammonia, which has a relative molecular mass of 17. 2. As such, nitrogen diffuses out of the porous pot faster than carbon dioxide diffuses in in the left beaker but slower out of the porous pot than ammonia gas diffuses in in the right beaker, causing water level at U to decrease. ACCEPT 1 m ammonia & carbon dioxide molecular mass calculated correct & correct use of diffusion concept 2 Mark scheme will use these abbreviations / + R A Ig ref ecf AW AVP ORA OWTTE underline ( ) alternatives statements on both sides of the + are needed for that mark reject accept (for answers correctly cued by the question) ignore as irrelevant with reference to error carried forward alternative wording (where responses vary more than usual) alternative valid point or reverse argument or words to that effect actual word given must be used by candidate (grammatical variants excepted) the word / phrase in brackets is not required but sets the context

7a argon and carbon dioxide 1 7b • Particles close together and orderly arrangement • At least 3 by 3 arrangement 7c 1. Oxygen particles change from sliding past one another to moving rapidly in any direction. 2. Oxygen particles change from being close together and disorderly, to far apart and disorderly. ACCEPT: 1m for liquid arrangement + movement 2 7d 1. Argon has an electronic configuration of 2, 8, 8. 2. It is unreactive as it has a fully-filled valence shell. 2 Section C – Free Response Questions Qn Marking Scheme Marks 8ai isotope number of protons number of neutrons number of electrons nuclide notation hydrogen 1 0 1 H11 deuterium 1 1 1 H12 tritium 1 2 2 H13 ACCEPT D for deuterium & T for tritium 1 8aii 1. Hydrogen, deuterium and tritium atoms contain one proton each 2. Deuterium atom has one more neutron than hydrogen atom, while tritium atom has two more neutrons than hydrogen atom / Hydrogen atom has one neutron, deuterium atom has two neutrons while tritium atom has three neutrons. 1m – understanding of isotope 1m – use of data 2 8aiii They all have one positively-charged proton and one negatively-charged electron/ equal number of positively-charged protons and negatively-charged electrons. 1 8aiv 1. D2O has similar chemical properties as H2O, hence heavy water will not disrupt biological processes/ used in the same way in the body 2. Deuterium atoms are twice as heavy as compared to hydrogen atoms, hence they can be detected using analytical techniques like Mass Spectrometry. ACCEPT: heavier and link it back to Mass Spectrometry (detect) 2

REJECT: monitor 1m for stating both correct properties without providing sufficient explanations to support 8bi name of ion chemical symbol number of electrons hydrogen ion H+ 0 hydride ion H– 2 1 8bii 2 8c 1. Like Group 1 metals, hydrogen atom only contains 1 electron in its valence shell. 2. However, hydrogen atoms can gain or lose 1 electron to form hydride / hydrogen ions, while Group 1 atoms only lose 1 electron to form ions with +1 charge. 1m for explaining using electrons OR ions for marking point 2 (do not need to talk about both) 2 9a Silver chloride is insoluble in water while most ionic compounds are soluble in water. REJECT: insoluble in water and ethanol, solubility property 1 9b 1. Silver chloride has a giant ionic lattice structure, 2. with strong electrostatic forces of attraction/ strong ionic bonds, 3. which requires a large amount of energy to overcome/ break, resulting in a high melting and boiling point. 3 Mg H 2+ – 2