ntate ligand. A complex ion of chromium(III) contains one ethanedioate ligand and four fluoride ligands. Determine the charge of this complex ion and the coordination number of chromium in this complex ion.","markscheme":"- Calculates the charge of the complex: $+3 + (-2) + 4(-1) = -3$, yielding a charge of $3-$ B1\n- Calculates the coordination number: $1 \\times 2$ (from the bidentate ethanedioate) $+ 4 \\times 1$ (from the monodentate fluorides) $= 6$ B1","marks":2,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"direct_calculation","label":"Direct Calculation","steps":[{"type":"text","order":0,"title":"Analyze the given components","content":"To solve this problem, we need to list all the components of the complex ion and their properties:\n\n* **Central metal ion:** Chromium(III), which means it has a charge of $+3$ (written as $\\text{Cr}^{3+}$).\n* **Bidentate ligand:** One ethanedioate ion, $\\text{C}_2\\text{O}_4^{2-}$, which has a charge of $-2$ and forms $2$ coordinate bonds.\n* **Monodentate ligand:** Four fluoride ions, $\\text{F}^-$, each having a charge of $-1$ and forming $1$ coordinate bond.","highlights":[{"text":"ethanedioate ion, \$\\text{C}_2\\text{O}_4^{2-}\$, is a bidentate ligand","location":"specification"},{"text":"chromium(III)","location":"specification"},{"text":"one ethanedioate ligand and four fluoride ligands","location":"specification"}]},{"type":"text","order":1,"title":"Calculate the coordination number","content":"The **coordination number** is the total number of coordinate bonds formed between the metal ion and the ligands.\n\n* **Ethanedioate ligand contribution:** Since it is bidentate, $1 \\text{ ligand} \\times 2 \\text{ bonds/ligand} = 2 \\text{ bonds}$\n* **Fluoride ligands contribution:** Since fluoride is a monodentate ligand, $4 \\text{ ligands} \\times 1 \\text{ bond/ligand} = 4 \\text{ bonds}$\n\nAdding these together:\n$$\\text{Coordination Number} = 2 + 4 = 6$$"},{"type":"text","order":2,"title":"Calculate the overall charge","content":"The overall **charge** of the complex ion is the sum of the charge of the central metal ion and the charges of all the ligands.\n\n$$\\text{Overall Charge} = \\text{Charge of } \\text{Cr}^{3+} + \\text{Charge of } \\text{C}_2\\text{O}_4^{2-} + 4 \\times (\\text{Charge of } \\text{F}^-)$$\n\nSubstituting the values:\n$$\\text{Overall Charge} = (+3) + (-2) + 4(-1)$$\n$$\\text{Overall Charge} = +3 - 2 - 4 = -3$$\n\nTherefore, the charge of the complex ion is **$3-$**."},{"type":"text","order":3,"title":"State the final answers","content":"The final parameters of the chromium(III) complex are:\n* **Charge of the complex ion:** $3-$ (or $-3$)\n* **Coordination number:** $6$"}]}],"generatedAt":"2026-06-11T09:08:47.298Z","modelVersion":"gemini-3.5-flash","explanationVersion":"v2"},"options":[]},{"id":"dd007fa2-81b1-4e6d-a81e-bff2fe251b28","label":"b","content":"An acidified solution containing dichromate(VI) ions, \$\\text{Cr}_2\\text{O}_7^{2-}\$, reacts with oxovanadium(IV) ions, \$\\text{VO}^{2+}\$, in a redox reaction to form a solution containing chromium(III) ions, \$\\text{Cr}^{3+}\$, and dioxovanadium(V) ions, \$\\text{VO}_2^+\$. Construct the overall balanced ionic equation for this reaction.","markscheme":"- Writes the correct reduction half-equation: $\\text{Cr}_2\\text{O}_7^{2-} + 14\\text{H}^+ + 6\\text{e}^- \\rightarrow 2\\text{Cr}^{3+} + 7\\text{H}_2\\text{O}$ M1\n- Writes the correct oxidation half-equation: $\\text{VO}^{2+} + \\text{H}_2\\text{O} \\rightarrow \\text{VO}_2^+ + 2\\text{H}^+ + \\text{e}^-$ M1\n- Multiplies the oxidation half-equation by $6$, combines, and simplifies to obtain the final balanced overall equation: $\\text{Cr}_2\\text{O}_7^{2-} + 2\\text{H}^+ + 6\\text{VO}^{2+} \\rightarrow 2\\text{Cr}^{3+} + \\text{H}_2\\text{O} + 6\\text{VO}_2^+$ A1","marks":3,"order":1,"markingRubric":null,"explanation":{"methods":[{"id":"half_equation","label":"Half-Equation Method","steps":[{"type":"text","order":0,"title":"Identify

Transition elements

Question 18

Transition elements Questions

Transition elements

Question 18

Transition elements Questions