Developing Metals Flashcards
Explain what is meant by a transition metal/ element.
A d-block element which forms one or more ions with an incomplete d-subshell.
What are general properties of metals?
- High mp/ bp point due to strong electrostatic attraction which requires a lot of energy to break.
- Electrical conductors due to delocalised electrons which are free to carry charge
- High density due to closely packed arrangement of particles.
What are properties specific to transition elements?
- Variable oxidation states
- Form coloured ions in solution
- Form complex ions with ligands
- Catalytic activity
What are the electronic configurations of chromium and copper?
The electronic configurations of chromium and copper are exceptions to the rule of filling up subshells:
* Chromium: 1s2,2s2,2p6,3s2,3p6,3d5,4s1
* Copper: 1s2,2s2,2p6,3s2,3p6,3d10,4s1
Should be in superscript and no commas!
What 2 oxidation states can Fe have?
Fe2+ or Fe3+
What 2 oxidation states can Cu have?
Cu+ and Cu2+
Colour of Fe2+ in solution.
pale green
Colour of Fe3+ in solution.
brown
Colour of Cu2+ in solution.
blue
Colour of Cu+ in solution.
colourless
What happens to Cu+ in solution and why?
Cu+ is unstable in solution and will disproportionate into Cu2+ and Cu readily.
2Cu+(aq) ⟶ Cu2+(aq) + Cu(s).
Explain what is meant by disproportionation?
The same element is oxidised and reduced in the same reaction.
What is a complex ion?
A complex ion has a central transition metal ion surrounded by other groups called ligands. E.g [Cu(H2O)6]2+
What is a ligand?
Ligands have a lone pair with which they form dative covalent (coordinate) bonds to the central ion. May be neutral or a negative ion. E.g. H2O:, :CN-
What is meant by monodentate?
Ligand forms 1 coordinate bond to the central metal ion, donating 1 electron pair.
What is meant by bidentate?
Ligand forms 2 coordinate bonds to the central metal ion, donating 2 electron pairs.
What is meant by hexadentate?
Ligand forms 6 coordinate bonds to the central metal ion, donating 6 electron pairs.
What is meant by polydentate?
Ligand forms many coordinate bonds to the central metal ion, donating many e- pairs.
Give examples of monodentate ligands.
- H2O:
- :NH
- :SCN-
- :CN-
- :Cl-
- :OH-
Give examples of bidentate ligands.
- Ethandioate ion
- Ethane-1,2-diamine
What is meant by coordination number?
The number of coordinate bonds from ligands to the central metal ion.
What are the 2 bond shapes associated in complex with a coordination number of 4?
Tetrahedral or Square Planar
What is the bond angle for a tetrahedral complex?
109.5°
What is the bond angle for a square planar complex?
90°
What is the bond shape for a complex ion with a coordination number of 6?
Octahedral
What is the bond angle for a complex ion with a coordination number of 6?
90°
What is ligand substitution reaction?
Where one ligand in a complex is replaced by another ligand.
What are some examples of complex ions of iron?
[Fe(H2O)6]2+ , [Fe(H2O)6]3+
What are some examples of complex ions of copper?
[Cu(H2O)6]2+ , [Cu(Cl)4]2- , [Cu(NH3)4]2+
What is a precipitation reaction?
When two ionic aqueous solutions react together to form an insoluble ionic solid, this is known as a precipitate.
How does iron(II) and iron (III) react with NaOH?
How does copper(II) react with NaOH?
How does iron(II) and iron (III) react with NH3(aq)?
How does copper(II) react with NH3(aq)?
Why do transition metals make good homogeneous catalysts?
- Since transition metals have various oxidation states, they make good homogeneous catalysts.
- This is because they are able to oxidise and reduce reactants and intermediates to form the desired products.
Why do transition metals make good heterogeneous catalysts?
Using the 3d and 4s electrons of the atoms on the catalyst surface, transition metals can form weak bonds with reactants which makes them more reactive.
Why are transition metals often coloured?
- When light is incident on an object, some is absorbed.
- It will only be absorbed if its energy equals the difference in energies between two energy levels of the atom.
- If it does, an electron becomes excited and is raised to a higher energy level.
- The difference in energy between the two energy levels is often equivalent to the wavelengths/frequencies of the visible region of the electromagnetic spectrum.
- Therefore transition metal complexes often appear coloured.
How to calculate the standard cell potential.
E cell =E°(+ve terminal) - E°(-ve terminal)
Measured in V volts.
What is a half cell?
A half cell contains the chemical species present in a redox half equation.
What is a metal/ metal ion half-cell?
Consist of an element in different oxidation states in equilibirum. e.g. Cu(s) + 2e- ⇌ Cu2+ (aq)
What is a metal ion/ metal ion half cell?
Consist of an element in two different oxidation states in equilibrium, where both species are ions. e.g. Fe2+ and Fe3+.
Fe3+ (aq) + e- ⇌ Fe2+
* The electrode is usually graphite or platinum
* An equimolar solution of each ion is required.
What is a non-metal/ ion half cell?
e.g. 2H+(aq) + 2e- ⇌ H2(g)
* Called a standard hydrogen half cell and E° = 0.00V
* Requires an inert platinum electrode coated in ‘platinum black’ to move e-.
What is the standard cell potential?
The potential difference of the electrochemical cell at standard conditions. It is the difference between the standard electrode potentials of the two half cells that it consists of.
What is standard electrode potential?
The potential difference between a half cell and a standard hydrogen half cell at 298K, 1 moldm-3 solutions, and gas pressure of 1 atm.
What is an electrochemical cell?
Consists of a redox reaction where two half reactions take place separately, and electron transfer between the reactions takes place along a wire (as an electric current) producing electrical energy. (Some energy is also lost as heat energy).
What does an electrochemical cell look like as a diagram?
What is a salt bridge?
- connects the two solutions, allowing the transfer of ions without letting the solutions to mix and possibly react.
- It is typically filter paper soacked in saturated KNO3(aq)
Why might graphite or platinum electrode be used?
They are very unreactive- i.e. will not react with the half cell solutions and will not affect the voltmeter readings. Usually used in ion/ion half cells.
How do you predict the feasibility of a redox reaction?
- The reaction is feasible if the oxidising agent has a lower standard cell potential than the reducing agent.
- The greater the difference in E° value, the more likely the reaction is to occur.
How do you predict which half-cell is being oxidised and which one is being reduced?
- Half cell with the more positive E° is oxidised
- Half cell with the more negative E° is reduced
What is rusting?
- Rust is an iron oxide, (usually red) formed from the redox reaction of iron and oxygen in the presence of water/moisture.
- Iron is oxidised, oxygen (dissolved in water) is reduced. The products of this redox reaction then react to form a hydrated iron oxide.
How do you prevent rusting?
- To protect iron from rust, the surface needs to be separated from air and water. i.e. by keeping the metal in oil.
- Coatings can be applied to iron.
- Alloys (e.g. stainless steel) can be made to prevent rusting.
What is a visible spectrohotometer?
It measures the amount of light transmitted or reflected, when incident on a solution, as a function of wavelength.
