1 This question is about compounds and ions of iron(II) and iron(III) that contain ethanedioate ions, C2O42–.
The C2O42– ion, shown below, is an example of a bidentate ligand.
i. Explain what is meant by the term bidentate ligand.
[2]
ii. A complex ion E contains three C2O42– ions bonded to an iron(III) ion in an octahedral shape.
Complex ion E exists as a mixture of two optical isomers.
Draw 3D diagrams to show the structures of the optical isomers of E.
Include any overall charge.
[3]
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, 2(a) This question is about the chemistry of compounds containing phosphorus.
Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, (b) When phosphorus(V) chloride, PCl5, and ammonium chloride are heated together, the compound P3N3Cl6 is
formed, together with HCl gas.
P3N3Cl6 has a cyclic structure, like the Kekulé structure of benzene.
i. Write an equation for the reaction of PCl5 and ammonium chloride to form P3N3Cl6.
[1]
ii. Calculate the percentage by mass of P in P3N3Cl6.
Give your answer to 2 decimal places.
percentage by mass of P = ................... % [2]
iii. Suggest one example of evidence that could show that P3N3Cl6 has a Kekulé structure rather than a
delocalised structure.
[1]
iv. In a molecule of P3N3Cl6 all the N and Cl atoms are bonded to P atoms.
Suggest a possible structure for a molecule of P3N3Cl6.
[2]
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, 3 This question is about the analysis of organic compounds.
A student investigates the alkaline hydrolysis of 1-bromopropane as outlined below.
Step 1 The student adds 1-bromopropane to an excess of aqueous potassium hydroxide, KOH(aq), in a pear-
shaped flask.
Step 2 A TLC chromatogram is run using propan-1-ol and the reaction mixture.
Step 3 The reaction mixture is refluxed.
A TLC chromatogram of the reaction mixture is run every 10 minutes.
The TLC chromatograms are shown below
i. Determine the Rf value of propan–1–ol.
Show your working.
Rf = ................... [1]
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The C2O42– ion, shown below, is an example of a bidentate ligand.
i. Explain what is meant by the term bidentate ligand.
[2]
ii. A complex ion E contains three C2O42– ions bonded to an iron(III) ion in an octahedral shape.
Complex ion E exists as a mixture of two optical isomers.
Draw 3D diagrams to show the structures of the optical isomers of E.
Include any overall charge.
[3]
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, 2(a) This question is about the chemistry of compounds containing phosphorus.
Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, (b) When phosphorus(V) chloride, PCl5, and ammonium chloride are heated together, the compound P3N3Cl6 is
formed, together with HCl gas.
P3N3Cl6 has a cyclic structure, like the Kekulé structure of benzene.
i. Write an equation for the reaction of PCl5 and ammonium chloride to form P3N3Cl6.
[1]
ii. Calculate the percentage by mass of P in P3N3Cl6.
Give your answer to 2 decimal places.
percentage by mass of P = ................... % [2]
iii. Suggest one example of evidence that could show that P3N3Cl6 has a Kekulé structure rather than a
delocalised structure.
[1]
iv. In a molecule of P3N3Cl6 all the N and Cl atoms are bonded to P atoms.
Suggest a possible structure for a molecule of P3N3Cl6.
[2]
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, 3 This question is about the analysis of organic compounds.
A student investigates the alkaline hydrolysis of 1-bromopropane as outlined below.
Step 1 The student adds 1-bromopropane to an excess of aqueous potassium hydroxide, KOH(aq), in a pear-
shaped flask.
Step 2 A TLC chromatogram is run using propan-1-ol and the reaction mixture.
Step 3 The reaction mixture is refluxed.
A TLC chromatogram of the reaction mixture is run every 10 minutes.
The TLC chromatograms are shown below
i. Determine the Rf value of propan–1–ol.
Show your working.
Rf = ................... [1]
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