2.3- Redox and group 7
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What is oxidation?
1) Gain of oxygen. 2) Loss of electrons. 3) An increase in oxidation state. 4) Loss of hydrogen.
What is reduction?
1) Loss of oxygen. 2) Gain of electrons. 3) Decrease in oxidation state. 4) Gain of hydrogen.
What does OIL RIG stand for?
Oxidation Is Loss (of electrons). Reduction Is Gain (of electrons).
What is the range of oxidation states for an element?
The maximum electrons that could be gained to the electrons that could be lost from within the same shell of an atom of an element.
What is the oxidation state of hydrogen?
+1 (except in metal hydrides).
What is the oxidation state of oxygen?
-2 (except in peroxides).
What are the oxidation states of very electronegative or electropositive elements e,g, group 1, group 2, group 7?
The oxidation states will be the same as their ion charge.
What are the rules for assigning oxidation states?
1) The oxidation state of any atom in an element is 0. 2) In ionic compounds, the oxidation state is the same as the charge on the ion. 3) In neutral molecules the sum of the oxidation states in 0. 4) In polyatomic ions (compound ions), the sum of the oxidation states equals the charge on the ion.
What does a half equation show?
EITHER the reduction OR the oxidation half of a redox reaction.
How do we balance half equations?
1) Number of atoms on either side of the arrow must balance. Sometimes you need to add H₂O and/or H+ to achieve this. 2) Charges must balance. Add the correct number of e- to the reactants or products to achieve this.
Can you increase the charge on one side of a half equation to make it match the charge on the other side?
NO- you can only decrease the charge of one side of the half equation by adding e- to that side.
If you add electrons to the LHS of a half-equation…
… you have written a reduction half equation.
If you add electrons to the RHS of a half-equation…
… you have written an oxidation half equation.
How do we combine half equations?
1) Find the lowest common multiple of the number of electrons in both of the half equations. 2) Multiply the whole of both half equations to make the number of electrons in both half-equations equal to the LCM. 3) Write the two modified half equations as one big equation, with reactants all on the left side and products all on the right side. 4) Cancel out the same number of electrons on both sides of the equation. 5) Cancel down any H+ and/or H₂O that may appear on both sides of the equation e.g. if there was 10H+ on the left and 2H+ on the right, this cancels down to 8H+ on the left.
What are oxidising agents?
Electron acceptor
Oxidising agents are themselves…
…reduced.
What are some examples of oxidising agents?
F₂, Cl₂, dichromate, Cr₆O₇2-
What are reducing agents?
Electron donors.
Reducing agents are themselves…
oxidised.
What are some examples of reducing agents?
Na, Li, Zn, NaBH₄
What is fluorine (F₂)?
1) Yellow gas. 2) Very reactive. 3) Toxic.
What is chlorine (Cl₂)?
1) Green gas. 2) Very reactive. 3) Toxic.
What is bromine (Br₂)?
1) Red-brown liquid. 2) Very reactive. 3) Toxic.
How is bromine often used as?
As a solution in water (bromine water- Br₂(aq)). This is orange.