Explain why complexes are coloured: ligands split the d orbitals and electrons absorb visible light when promoted between them, so the colour seen is complementary to the colour absorbed; use the colour wheel to deduce the absorbed wavelength and frequency.
Tę umiejętność sprawdza 37 zadań wzorowanych na arkuszach IB z lat 2022–2026.
(i) Iron, Fe, is a transition element. State two properties typical of transition elements that iron shows, other than the formation of coloured compounds. (ii) Explain why aqueous solutions containing the hexaaquacopper(II) ion, [Cu(H2O)6]2+,…
Colorimetry is an alternative technique for determining concentration. Iron(II) ions can be converted to a red complex ion by adding 1,10-phenanthroline. (i) Outline why the concentration of iron(II) in a solution can be measured by colorimetry after this…
The copper(II) ion, Cu2+, forms a variety of coloured complexes. (i) Outline, with a reason, why solutions containing [Cu(H2O)6]2+ ions are blue. Use section 15 of the data booklet. (ii) State the type of bond between the copper(II) ion and…
Explain the origin of the colours of the nickel complexes.
The complex ion [Zn(H2O)6]2+ is colourless, but the complex ion [Cu(H2O)6]2+ is blue. Which option gives a correct reason for the zinc complex and the electron configuration of the copper(II) ion? A. Light is absorbed when an electron is…
The table shows the observed colour of three octahedral complex ions formed by the same metal ion, M2+, with different ligands. Which statement about these complex ions and their colours is correct? A. Splitting of the d-orbitals is greatest in…
Portions of the rinse water were then titrated with the standardized EDTA solution in the presence of murexide as indicator. The burette readings are given in the table. (i) Suggest two reasons why trial 1 required a much larger volume of EDTA than the other…
The cyanide ion acts as a ligand in many complex ions, for example hexacyanoferrate(III), [Fe(CN)6]3−. (i) State the type of bond, as precisely as possible, that joins each cyanide ion to the iron ion. (ii) Deduce the oxidation state of iron in…
Each indicator contains more than one benzene ring. (i) State one functional group, other than the phenyl group, that is present in all three indicators. (ii) Deduce the colour of light absorbed by bromothymol blue in acidic conditions and by bromophenol blue…
Draw a line of best fit on the graph, extrapolating it beyond the range of the data.
State, in mathematical terms, how the absorbance of these solutions depends on their concentration.
The colorimeter can record either absorbance or percentage transmittance at a chosen wavelength. Outline why one particular wavelength has to be selected.
Deduce the equation that relates absorbance to concentration for these solutions, including the numerical value of the constant.
Estimate the absorbance of a 0.400 mol dm−3 solution of nickel(II) sulfate.
Predict the difference, if any, between the absorbance of the 0.400 mol dm−3 solution read from the extrapolated line and the value calculated from the equation in 3d.
Nickel(II) sulfate solution is green. Deduce the most suitable wavelength for this colorimetry, using section 15 of the data booklet.
In the first step, manganese(III) ions formed from the manganate(VII) are complexed by ethanedioate ions. [Mn(H2O)6]3+(aq) + 2 C2O42−(aq) → [Mn(C2O4)2(H2O)2]−(aq) + 4 H2O(l) (i) Deduce the oxidation state of carbon in [Mn(C2O4)2(H2O)2]−. (ii)…
An aqueous solution of nickel(II) sulfate, which contains the [Ni(H2O)6]2+ ion, is green. Which statement explains the origin of this colour? A. Red light is absorbed when electrons are promoted between the split d orbitals of the nickel ion. B. Red…
Anhydrous nickel(II) chloride is yellow, whereas magnesium chloride is white. (i) State nickel's condensed electron configuration. (ii) In terms of electron configuration, state why nickel(II) chloride is a coloured compound. (iii) Nickel(II) chloride absorbs…
Aqueous nickel(II) ions, [Ni(H2O)6]2+, appear green. Which statements correctly account for this colour? I. Red light is absorbed when an electron is promoted from the lower to the higher set of split d-orbitals. II. Green light is emitted when…
Which ion is likely to form a coloured aqueous solution, based on its electron configuration? A. Ag+ B. Ti4+ C. Cd2+ D. Cr3+
Chloride ions can act as ligands towards transition metal ions. Three compounds of chromium that differ in the number of chloride ions bonded directly to the chromium ion have the formulas and colours shown. (i) Deduce the charge of the complex ion in…
Aqueous solutions of nickel(II) sulfate, which contain [Ni(H2O)6]2+ ions, are green. Use section 15 of the data booklet. Which statement explains the colour? A. Green light is absorbed when an electron is promoted between the split 3d orbitals. B.…
Explain the colour of Co2+(aq) in terms of its electronic structure, using section 15 of the data booklet.
The complex ion [Cr(H2O)6]3+ is violet and absorbs light most strongly at about 580 nm. The complex ion [Cr(NH3)6]3+ is orange and absorbs light most strongly at about 465 nm. (i) Explain why the two complex ions have different colours. Use…
[Ni(H2O)6]2+ is green, whereas [Ni(NH3)6]2+ is blue. Which statement best accounts for the different colours of the two complex ions? A. The two sets of ligands give different energy gaps between the split 3d orbitals, so light of different…
A pale blue solution of [Cu(H2O)6]2+ turns deep blue when aqueous ammonia is added in excess and the complex ion [Cu(NH3)4(H2O)2]2+ forms. Which factor explains the change in colour? A. Charge on the metal ion B. Number of d electrons in the…
Nickel forms the chloride NiCl2. (i) State the full electron configuration of the nickel(II) ion, Ni2+. (ii) In aqueous solution nickel(II) ions exist as [Ni(H2O)6]2+, which is green. Describe the interaction between the nickel ion and a…
A colorimeter is set to a wavelength of 550 nm. Explain why it cannot be used to follow reactions of compounds of Sc3+. Use section 5 of the data booklet.
Ultraviolet (UV) light is being investigated as a way of killing micro-organisms in juice without heating it, so that less vitamin C is lost. The absorption spectrum of a dilute aqueous solution of sorbic acid, a preservative that is added to some bottled…
Which solutions would show a wavelength of maximum absorbance different from that of 0.10 mol dm−3 CuSO4(aq)? I. 0.010 mol dm−3 CuSO4 II. 0.10 mol dm−3 Cu(NO3)2 III.…
The wavelength of maximum absorbance of an aqueous solution of 0.10 mol dm−3 CuSO4 is measured. Which aqueous solutions would have a different wavelength of maximum absorbance? I. 0.050 mol dm−3 Cu(NO3)2 II.…
Methyl orange is a synthetic dye that is used as an acid–base indicator. The absorption spectrum of methyl orange in acidic solution is shown. Identify the colour of the acidic solution and give a reason. Use section 15 of the data booklet.
Explain why the complex ion [Cu(NH3)4]2+ is coloured.
A solution of hydrated nickel(II) ions, [Ni(H2O)6]2+, is green. Which statement explains the colour? A. Green light is absorbed when electrons are promoted between d-orbitals B. Light complementary to green is absorbed when electrons are promoted…
The complex ion [Co(H2O)6]3+ is blue and the complex ion [Co(NH3)6]3+ is orange. The colour absorbed by a complex is complementary to the colour observed. The colour wheel gives the wavelength of light of each colour. What is correct about the…
An aqueous solution of copper(II) sulfate is blue because of the [Cu(H2O)6]2+ ion. Use section 15 of the data booklet if needed. Which statement best explains the colour? A. Blue light is absorbed when electrons are promoted between split d orbitals…
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