The method and the results are on the transition metals lab. Do the analysis yourself first, then check the answers below.
Quick answer: Transition metals are d-block elements that form ions with a partially filled d subshell. These answers go with the Chemistry 11-12 lab on transition metals: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
These model answers use the sample table. Colours and the through-origin gradient should match closely; expect your own absorbances to differ slightly, but the straight-line pattern must be clear.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.2.5
Chloride ions are bigger than water molecules, so only four chloride ligands fit, giving tetrahedral [CuCl₄]²⁻. Water shifts the equilibrium back toward [Cu(H₂O)₆]²⁺, which is blue.
Question 4 Calibration graph
The points lie close to a straight line through the origin, showing absorbance is directly proportional to concentration (Beer-Lambert behaviour).
Question 5 Molar absorptivity
Slope = Σ(Ac) ÷ Σc² = 0.0898 ÷ 0.012 = 7.5 dm³ mol⁻¹; it measures how strongly the complex absorbs at 600 nm for a 1 cm cell.
Question 6 Unknown solution
c = 0.36 ÷ 7.5 = 0.048 mol dm⁻³ for the diluted sample; the dilution was ×5, so the original is 0.24 mol dm⁻³.
Question 7 Why a filter
The complex absorbs orange-red light most strongly, so the filter picks the wavelength with the greatest absorbance for a sensitive reading.
Question 8 Improvements
Use a volumetric pipette and flask for the dilutions, and repeat each absorbance reading three times and average them. Zero the colorimeter with a water blank each time.
