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OCR B A Level Chemistry > Developing Metals > Flashcards

Flashcards in Developing Metals Deck (13)
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1

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!

2

What is the meaning of co-ordination number?

the number of lone pairs donated by ligands to the metal ion

3

A reaction is predicted to occur from redox potential values. Why might the reaction not occur?

The activation enthalpy is large

4

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?

MnO4–(aq)
Mn2+(aq)
H+(aq)

5

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

6

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

7

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

8

What is a reducing agent?

A species that donates its electrons to reduce another species in a redox reaction, which itself is oxidised

9

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

10

How can half equations be balanced?

Balancing the charges by using electrons
If the oxidising agent contains oxygen, H+ or H2O can be used

11

Explain the meaning of the term 'complex'

A central metal ion/atom that is surrounded by ligands

12

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

13

Explain the meaning of the term 'polydentate'

A ligand that can form more than one bond to the central atom/ion