AQA A-LEVEL Chemistry 7405-1 Paper 1 Mark Scheme.

Question Answers Additional comments/Guidelines Mark 01.1 M1 ΔfH = ΔaH (Sr) + 2ΔaH (Cl) + Δ1st IEH (Sr) + Δ2nd IEH (Sr) + 2ΔEAH(Cl) + ΔLEH (Sr) 1 Or – 828 = 164 + (2 x 121) + 548 + 1060 + (2 x ΔEAH) + (– 2112) 1 M2 2 x ΔEAH = – 730 M3 ΔEAH = – 365 (kJ mol–1) Allow M3 = M2÷2 1 (+) 365, –304.5, and –730 = 2 marks (+) 304.5, (+) 730 and –609 = 1 mark (+) 609 = 0 marks 11 01.3 (Has) covalent character or partial covalent bonding (as well as ionic bonding) Allow chloride ion has been polarised or chloride ion distorted Ignore not perfectly ionic Ignore ions are not spheres Do not allow references to molecules or ions with covalent character Do not allow it is covalently bonded alone 1 01.4 M1 (From Li+ to K+) size (of ion) increases OR charge density (of ion) decreases M1 Allow K+ has more shells or larger distance between nucleus and outer electrons or larger ionic radius Do not allow atomic radius or molecules 1 M2 (Electrostatic) attraction between metal ion and Oδ– of water decreases or attraction between lone pair on O and + ion decreases M2 Not dependent on M1 Allow converse arguments 1 01.5 M1 ΔsolH = ΔLEdissociationH + ΔhydH (Ca2+) + 2x ΔhydH (Br–) 1 or M1 – 110 = 2176 + (– 1650) + 2x ΔhydH (Br–) M2 (2x ΔhydH (Br–)) = – 636 1 M3 ΔhydH (Br–) = – 318 (kJ mol–1) Allow M3 = M2 ÷ 2 1 (+)1858, (+)318 and –636 = 2 marks +3716, –1858 and (+)636 = 1 mark –3716 = 0 marks Question Answers Additional comments/Guidelines Mark 02.1 Average / mean mass of 1 atom (of an element) 1/12 mass of one atom of 12C OR Average / mean mass of atoms of an element 1/12 mass of one atom of 12C OR Average / mean mass of atoms of an element ×12 mass of one atom of 12C OR (Average) mass of one mole of atoms 1/12 mass of one mole of 12C OR (Weighted) average mass of all the isotopes 1/12 mass of one atom of 12C OR Average mass of an atom/isotope compared to/relative to C−12 on a scale in which an atom of C−12 has a mass of 12 This expression = 2 marks If moles and atoms mixed, max = 1 Mark top and bottom line independently. All key terms must be present for each mark. 1 1 02.2 M1 % of 50Cr and 53Cr = 13.9% Let % of 53Cr = x% and Let % of 50Cr = (13.9 - x)% M2 52.1 = 50(13.9 - x) + (52 x 86.1) + 53( x) 100 OR 3x = 37.8 M3 x = % of 53Cr = 12.6% M4 % of 50Cr = 1.3% If x used for 50Cr and 53Cr or x and y, max 2 marks = M1 and M4 Alternative M2 Let % of 53Cr = (13.9%-x)% and % of 50Cr = x% M2 52.1 = 53(13.9 - x)+(52 x 86.1)+50x 100 OR 3x = 3.9 M4 = M1- M3 1 1 1 1 02.3 M1 (Same) number of protons OR electrons M2 (Different) number of neutrons Do not allow same electronic configuration for M1 1 1 02.4 M1 (Ions will interact with and) be accelerated (by an electric field) M2 Ions create a current when hitting the detector OR ions create a current in the detector/electron multiplier. Allow (ions) accelerated to a negative plate Do not allow magnetic field Allow (ions) can be detected 1 1