Flashcards in Developing Metals Deck (13)
Which statement is true for all transition metal elements?
Statement 1: Their ions can form complexes with ligands.
Statement 2: They can form compounds in which the metal has a positive or negative oxidation state.
Statement 3: They form ions with a partially filled 3d sub-shell.
Statement 1 is true. Statement 2 is untrue – they are able to form positive or negative ions but the oxidation state of the transition metal is always positive. Statement 3 is also untrue –the d-block contains more than one period!
What is the meaning of co-ordination number?
the number of lone pairs donated by ligands to the metal ion
A reaction is predicted to occur from redox potential values. Why might the reaction not occur?
The activation enthalpy is large
A student sets up a half-cell for the reaction shown. 8H+ + MnO4– + 5e– → Mn2+ + 4H2O
What solution(s) does the student place in the beaker?
Explain how cobalt compounds can absorb light. (3 marks)
d electrons are split by the ligands
electrons move up energy levels
absorb light since ∆E= hv
Describe the colour changes and reactions that occur when Fe2+(aq), Fe3+(aq), and Cu2+(aq) ions react with NH3(aq) and NaOH(aq). (6 marks)
colours of aqueous solutions:
Cu2+ is blue. Fe2+ is green. Fe3+ is yellow/brown
addition of NaOH:
precipitates of hydroxides formed. copper is (pale) blue. iron(II) is dark green. iron(III) is brown/red
addition of NH3:
copper(II) hexaaqua dissolves in excess ammonia to give dark blue solution. iron precipitates don't dissolve
A student has test-tubes containing solutions of 0.10 mol dm–3, 0.20 mol dm–3, 0.30 mol dm–3, and 0.40 mol dm–3 of MnO4– ions. How could they use colorimetry to measure the concentration of a solution?
Use colorimeter with green/yellow filter
Measure absorbance of all MnO4– solutions
Plot calibration curve of concentration against absorbance
Measure absorbance of unknown and read off concentration from graph
What is a reducing agent?
A species that donates its electrons to reduce another species in a redox reaction, which itself is oxidised
What is an oxidising agent?
A species that gains electrons from another species that's being oxidised in a redox reaction, which itself is reduced
How can half equations be balanced?
Balancing the charges by using electrons
If the oxidising agent contains oxygen, H+ or H2O can be used
Explain the meaning of the term 'complex'
A central metal ion/atom that is surrounded by ligands
Explain the meaning of the term 'ligand'
A molecule/ion that has at least one lone pair of electrons, that can form dative covalent bonds