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OCR A Specimen Paper 1 Q22
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![22 A student carries out a number of experiments on transition metal compounds. 26 4.800 g of a green hydrated crystalline solid A are heated in a crucible to remove the water of crystallisation. 1.944 g of water are removed to leave 0.0180 mol of solid residue B. Solid B contains 32.8%, by mass, of the transition metal. All of B is reacted with AgNO3(aq) to form 7.695 g of a white precipitate, C. The green crystalline solid A is dissolved in water to produce a green solution containing a complex ion, D. When aqueous sodium hydroxide is added to solution of D, a greygreen precipitate, E, is observed, which dissolves in excess aqueous sodium hydroxide to form a green solution. (a) Determine the formulae of A, B, D and E. Show all your working. Specimen A =B =D =E =OCR 2014 H432/01 [9]<br />
27 (b)* Transition metal complexes often have different shapes and may form a number of stereoisomers. Describe the different shapes and the different types of stereoisomerism found in transition metal chemistry. Use suitable examples and diagrams in your answer. Specimen . . . . . . . . .END OF QUESTION PAPEROCR 2014 H432/01 [6]<br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_QP_-_Paper_1_OCR_Chemistry_A_A-Level_22-0.jpg)
![H432/01 Question 22 (a) Mark Scheme June 20XX Marks Guidance Answer 1. n(AgCl) formed = 7.695 = 0.05362 (mol) (cid:51) 143.5 2. 0.0180 mol of B forms 0.05362 mol of Cl No of Cl ions in formula of B = 0.05362 = 3 (cid:51) 0.0180 3. Molar mass of B = 2.856 = 158.7 (g mol1) (cid:51) 0.0180 158.7(335.5) = 52.2 which is chromium (cid:51) 4. n(H2O) = 1.944 = 0.108 (mol) 18 0.0180 mol CrCl3: 0.108 mol H2O OR 1 mol CrCl3: 6 mol H2O (cid:51) A CrCl36H2O (from points 2, 3 and 4) (cid:51) B CrCl3 (from points 2 and 3) (cid:51) D [Cr(H2O)6]3+ (from determination of A and understanding of reaction with water) (cid:51) E Cr(OH)3 (from understanding of reaction of D with aqueous hydroxide) (cid:51) Specimen ALLOW Alternative working throughout 20 P M T<br />
H432/01 Question (b)* Answer Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. Level 3 (56 marks) Links together names of shapes with correct 3-D diagrams AND Appreciates the two different types of isomerism and labels diagrams appropriately There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Demonstrates clear and confident knowledge of relevant technical language using the termsnon-superimposable mirror images within optical isomerismopposite and adjacent/same side in cistrans Level 2 (34 marks) Names and labels at least two of the shapes appropriately giving 3-D diagrams AND Appreciates that two types of isomerism exist in transition metal chemistry, gives diagrams to illustrate at least one pair of isomers and names them correctly There is a line of reasoning presented with some structure. The information presented is in the most-part relevant and supported by some evidence. Answers question with a sound grasp of relevant technical language using the terms H2O OH2 Cu OH2 H2O OH2 OH2 Octahedral Specimen OR 21 Mark Scheme June 20XX Marks Guidance Indicative scientific points may include: Shapes of complex ionssix coordinate bonds: octahedral3-D diagrams with charges linked to shapes four coordinate bonds: tetrahedral or square planar 2- 2+ Cl Cu Cl Cl Tetrahedral Cl Cl Cl Pt NH3 H3N Square Planar cistrans isomerism3-D diagrams to illustrate found in octahedral and square planar complexes transopposite; cisadjacent / same side P M T<br />
H432/01 Question tetrahedral, octahedral cistrans OR opticalLevel 1 (12 marks) Names and draws structures of two of the shapes AND Appreciates one type of isomerism that can be seen in transition metal chemistry The information is basic and communicated in an unstructured way. The information is supported by limited evidence and the relationship to the evidence may not be clear. Answers question with a basic grasp of relevant technical languagelinks octahedral to six ligands and tetrahedral to four ligands either in word or by diagramcorrectly links one type of isomerism to a structure 0 marks No response or no response worthy of credit. H2C Cl H2N Cl Cr Specimen OR Total 15 H2 C N2H H2N H2C H2C C H2 Mark Scheme June 20XX Answer Marks Guidance Optical isomerismFound in octahedral complexes when bidentate ligands are present Isomers are non-superimposable mirror images3-D diagrams to illustrate 2+ H2C H2C NH2 Cl Cr N H2 H2N Cl NH2 CH2 C H2 NH2 CH2 N H2 CH2 2+ 2+ NH2 C H2 NH2 Ni NH2 NH2 CH2 N H2 CH2 H2C H2C H2N NH2 Ni N H2 H2N H2 C 2+ CH2 HN2 NH2 CH2 C H2 22 P M T<br />](https://learnah.org/wp-content/uploads/2018/08/Specimen_MS_-_Paper_1_OCR_Chemistry_A_A-Level_22-0.jpg)
