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Edexcel Jun 2016 (IAL) Paper 5 Q
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![A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D 21 Chromium is in the d-block of the Periodic Table and it is a transition metal. (a) Scandium is also in the d-block of the Periodic Table but it is not a transition metal. Explain, by giving any relevant electronic configurations, why scandium is not a transition metal. (3)(b) When a few drops of aqueous ammonia are added to an aqueous solution of chromium(III) ions, a green precipitate of chromium(III) hydroxide is formed. Complete the ionic equation for this reaction. State symbols are not required. [Cr(H2O)6]3+ +NH3 (cid:314) (c) Explain, in terms of oxidation numbers of chromium, whether or not each of these two reactions are redox. Cr2O7 2CrO4 2 + 14H+ + 6Fe2+ (cid:314) 2Cr3+ + 7H2O + 6Fe3+ Reaction 1 2 + 2H+ (cid:314) Cr2O7 2 + H2O Reaction 2 (2) (2)*P46665A01932* 19 Turn over<br />
(d) Chromium(III) chloride can exist in aqueous solution as three possible complex ions with different numbers of free chloride ions. Complex ion Free chloride ions [Cr(H2O)6]3+ [CrCl(H2O)5]2+ [CrCl2(H2O)4]+ 3Cl 2Cl Cl (i) There are two possible structures for complex ion Z. Complete the diagrams below to show the two possible structures for complex ion Z.CrCr D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A (2) (2) (ii) Name the type of bond between the ligands and the chromium(III) ion and explain how it is formed.20 *P46665A02032* D O N O T W R I T E I N T H I S A R E A<br />
(iii) The formula of the complex ion present in the solution is found by adding aqueous silver nitrate to the solution. This only reacts with the free chloride ions to form a precipitate of silver chloride. Ag+(aq) + Cl(aq) (cid:314) AgCl(s) The precipitate is then filtered, washed, dried and weighed. In an experiment, 0.012 mol of one of the forms of chromium(III) chloride was used and 3.44g of silver chloride was formed. Deduce the formula of the complex ion. You must show your working. (3) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (Total for Question 21 = 14 marks) *P46665A02132* 21 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJune_2016_IAL_QP_-_Unit_5_Edexcel_Chemistry_21-0.jpg)
![Mark (3) Reject d shell sub-shell / orbital other than 3d Acceptable Answers Transition metals form at least one ion with an incomplete d-subshell / partially filled d orbital(s) ALLOW forms an ion with unpaired d electron(s) OR Scandium only forms an ion with an empty d-subshell / all d orbitals are empty OR Scandium does not form an ion with an incomplete d-subshell / partially filled d (1) orbital(s) Scandium (only) forms Sc3+ ALLOW Sc only has one oxidation state (in compounds) (1) Sc3+ is [Ar] OR Sc is [Ar]3d14s2 / [Ar]4s23d1 and loses all three outer electrons ALLOW [Ar] written out as 1s22s22p63s23p6 (1) Question Number 21(a)<br />
Acceptable Answers Reject Mark (2) Acceptable Answers ALLOW oxidation numbers written by formulae in equations Reject Mark (2) First mark Reaction 1 is a redox reaction as chromium decreases / changes in oxidation number from (+)6 / VI to (+)3 / III (1) Second mark Reaction 2 is not a redox reaction as chromium has oxidation number (+)6(+) 2 / reactant and 2 and Cr2O7 / VI in CrO4 product / both species (1) IGNORE change in oxidation number of iron [Cr(H2O)6]3+ + 3NH3OR [Cr(H2O)6]3+ + 3NH3Cr(OH)3 + 3H2O + 3NH4 Any equation where NH3 replaces water ligands [Cr(OH)3(H2O)3] + 3NH4 Correct formula of chromium(III) hydroxide ALLOW [Cr(H2O)3(OH)3] (1) IGNORE square brackets Rest of equation and balancing Conditional on correct formula of chromium(III) hydroxide (1) IGNORE state symbols even if incorrect Question Number 21(b) Question Number 21(c)<br />
Question Number 21(d)(i) Acceptable Answers In both complexes: Reject Mark (2) IGNORE charges on ions (Cl- or Cr3+) inside the brackets IGNORE exact position of dative bond from the water Any complex ion showing the two chloride ligands in the cis positions where Cl-Cr-Cl bond angle is 90o e.g. (1) Any complex ion showing the two chloride ligands in the trans positions where Cl-Cr-Cl bond angle is 180o e.g. (1) ALLOW for one mark two diagrams with correct chlorine, but no water OR two diagrams with correct water, but no chlorines ALLOW for one mark two diagrams with Cl2 instead of Cl<br />
Mark Mark Reject No TE on incorrect moles Question Number 21(d)(ii) Acceptable Answers Reject dative(covalent) ALLOW co-ordinate (covalent/ bonding) (1) (formed from) the lone pair (of electrons) on the oxygen / chloride ion / ligand / water (to the chromium ion) (1) ALLOW pair of electrons for lone pair IGNORE element / molecule / atom Question Number 21(d)(iii) Working is essential Acceptable Answers mol of AgCl = 3.44/143.4 = 0.023989 (1) ratio Cr3+: (free Cl) (= 0.012: 0.023989) = 1 : 2 ALLOW this written in words (1) so, [CrCl(H2O)5]2+ / (ion) Y (is formed) (1) ALLOW structure of Y drawn IGNORE SF except 1SF ALLOW for two marks Y if 178.8 used for Mr X if 107.8 / 82.5 used for Mr If no other mark is awarded: ALLOW 1 mark for just [CrCl(H2O)5]2+ / (ion) Y (is formed) (Total for Question 21 = 14 marks)<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_IAL_MS_-_Unit_5_Edexcel_Chemistry_21-0.jpg)
