11. Group 17
A section of Chemistry, 9701
Listing 10 of 617 questions
Explain why chromium complexes are coloured. Four different compounds can be obtained when anhydrous chromium(chloride reacts with water under various conditions. When samples of each compound are reacted separately with aqueous silvernitrate, different amounts of silverchloride are precipitated. The precipitation leaves the complex ions P, Q, R and S in solution. formula of compound moles of AgCl precipitated per mole of complex ion complex ion property of complex ion CrCl 3(H2O)6 P non-polar CrCl 3(H2O)5 Q polar CrCl 3(H2O)4 R polar CrCl 3(H2O)4 S non-polar Draw three-dimensional diagrams for the structures of complex ions P, Q, R and S. Include the charges for each complex ion. P Cr Q Cr R Cr S Cr  Suggest why complex ion S is non-polar. The structure of picolinicacid is shown. picolinic acid CO2H N The conjugate base of picolinicacid is a bidentate ligand, Z. Define the term bidentate ligand. Draw the structure of Z.  Z reacts with aqueous chromium(ions, [Cr(H2O)6]3+, in a 3 : 1 ratio to form a new neutral complex. State the coordination number and the geometry of the chromium(centre in the complex. coordination number geometry ����������������������������������������� (NH4)2Cr2O7 decomposes readily on heating to form Cr2O3, steam and an inert colourless gas. Deduce the oxidation numbers of chromium in (NH4)2Cr2O7 and in Cr2O3. (NH4)2Cr2O7 Cr2O3 ��������������������������������������������������� Construct an equation for the thermal decomposition of (NH4)2Cr2O7. 
9701_s21_qp_41
THEORY
2021
Paper 4, Variant 1
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Explain why chromium complexes are coloured. Four different compounds can be obtained when anhydrous chromium(chloride reacts with water under various conditions. When samples of each compound are reacted separately with aqueous silvernitrate, different amounts of silverchloride are precipitated. The precipitation leaves the complex ions P, Q, R and S in solution. formula of compound moles of AgCl precipitated per mole of complex ion complex ion property of complex ion CrCl 3(H2O)6 P non-polar CrCl 3(H2O)5 Q polar CrCl 3(H2O)4 R polar CrCl 3(H2O)4 S non-polar Draw three-dimensional diagrams for the structures of complex ions P, Q, R and S. Include the charges for each complex ion. P Cr Q Cr R Cr S Cr  Suggest why complex ion S is non-polar. The structure of picolinicacid is shown. picolinic acid CO2H N The conjugate base of picolinicacid is a bidentate ligand, Z. Define the term bidentate ligand. Draw the structure of Z.  Z reacts with aqueous chromium(ions, [Cr(H2O)6]3+, in a 3 : 1 ratio to form a new neutral complex. State the coordination number and the geometry of the chromium(centre in the complex. coordination number geometry ����������������������������������������� (NH4)2Cr2O7 decomposes readily on heating to form Cr2O3, steam and an inert colourless gas. Deduce the oxidation numbers of chromium in (NH4)2Cr2O7 and in Cr2O3. (NH4)2Cr2O7 Cr2O3 ��������������������������������������������������� Construct an equation for the thermal decomposition of (NH4)2Cr2O7. 
9701_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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The elements of Group 17 are called halogens. Complete Table 1.1. Table 1.1 halogen colour at 293 K chlorine bromine iodine State the trend in volatility of the halogens chlorine, bromine and iodine. Explain your answer. Iodine is made by reacting bromine with sodium iodide. Construct an ionic equation for the reaction of bromine with sodium iodide. State the role of bromine in the reaction. Explain your answer. Concentrated sulfuric acid is added to separate samples containing equal amounts of NaCl , NaBr and NaI. All three samples initially react to produce the hydrogen halide. Write an equation to describe the acid–base reaction that occurs when concentrated sulfuric acid reacts with NaBr. Deduce which sodium halide, NaCl , NaBr or NaI, produces the largest percentage yield of hydrogen halide when concentrated sulfuric acid is added. Explain your answer by considering the relative reactivity of the halide ions as reducing agents. identity of sodium halide explanation
9701_s24_qp_21
THEORY
2024
Paper 2, Variant 1
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