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AQA Specimen Paper 1 Q8
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![22 0 8 . 1 A co-ordinate bond is formed when a transition metal ion reacts with a ligand. Explain how this co-ordinate bond is formed. [2 marks] . 2 0 8 Describe what you would observe when dilute aqueous ammonia is added dropwise, to excess, to an aqueous solution containing copper(II) ions. Write equations for the reactions that occur. [4 marks] Barcode Typesetter code<br />
23 0 8 . 3 When the complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane, the ammonia molecules but not the water molecules are replaced. Write an equation for this reaction. [1 mark] . 4 0 8 Suggest why the enthalpy change for the reaction in Question 8.3 is approximately zero. [2 marks] . 5 0 8 Explain why the reaction in Question 8.3 occurs despite having an enthalpy change that is approximately zero. [2 marks] Turn over for the next question Barcode Typesetter code Turn over <br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_QP_-_Paper_1_AQA_Chemistry_A-Level_8-0.jpg)
![MARK SCHEMEA-level ChemistrySpecimen paper 1 Marking guidance Mark AO Comments An electron pair on the ligand Is donated from the ligand to the central metal ion Blue precipitate Dissolves to give a dark blue solution [Cu(H2O)6]2+ + 2NH3 Cu(H2O)4(OH)2 + 2NH4 Cu(H2O)4(OH)2 + 4NH3 [Cu(NH3)4(H2O)2]2+ + 2OH + 2H2O [Cu(NH3)4(H2O)2]2+ + 2H2NCH2CH2NH2 [Cu(H2NCH2CH2NH2)2(H2O)2]2+ + 4NH3 CuN bonds formed have similar enthalpy / energy to CuN bonds broken And the same number of bonds broken and made 3 particles form 5 particles / disorder increases because more particles are formed / entropy change is positive Therefore, the free-energy change is negative 1 1 1 1 1 1 1 1 1 AO1a AO1a AO1b AO1b AO2d AO2d AO2b AO3 1b AO3 1b AO2e AO2e M2 can only be awarded if M1 is correct 13 of 15 Question 08.1 08.2 08.3 08.4 08.5<br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_MS_-_Paper_1_AQA_Chemistry_A-Level_8.jpg)