7. Oxidation, Reduction & Redox Flashcards
What is oxidation?
Loss of electrons, gain of oxygen
What is reduction?
Gain of electrons, loss of oxygen
What is a redox reaction?
In any reaction where an element is oxidised, and another must be reduced
What happens if an element itself is oxidised?
It must reduce the other element (by donating electrons)
What is the element that is oxidised known as?
The reducing agent (reductant)
Why is the element that is oxidised known as the reducing agent?
It must reduce the element by donating electrons
What happens if an element itself is reduced?
It must oxidise the other element (by accepting electrons)
What is the element that is reduced known as?
The oxidising agent (oxidant)
Why is the element that is reduced known as the oxidising agent?
It must oxidise the element by accepting electrons
What is used when it is unclear which element has been oxidised and which reduced?
Oxidation number/state of an element
Are S block metals oxidising or reducing agents?
Reducing - they lose electrons in reactions and so are oxidised
Do s block metals have positive or negative oxidation numbers?
Positive
Which elements will need to have their oxidation numbers worked out?
P and d block elements
Why do p and d block elements have to have their oxidation numbers worked out?
They can exhibit more than one oxidation state when they form compounds
Are halogens oxidising or reducing agents?
Oxidising - they gain electrons and so are reduced
Which element in a compound is taken as the one with a negative oxidation state?
The most electronegative element
Why is the most electronegative element the one with a negative oxidation state?
It has more power to withdraw electron density
Oxidation state of an uncombined element?
Zero
Oxidation state of a simple ion? Are there any exceptions to this?
Charge on ion - exception in some cases (e.g. halogens, hydrogen, oxygen)
Oxidation state of group 1 elements in a compound? Are there any exceptions to this?
+1 - no exceptions
Oxidation state of group 2 elements in a compound? Are there any exceptions to this?
+2 - no exceptions
Oxidation state of fluorine? Are there any exceptions to this?
-1 - no exceptions
Oxidation state of oxygen? Are there any exceptions to this?
-2 - except when in peroxides and combined with F
Oxidation state of hydrogen? Are there any exceptions to this?
+1 - except in metal hydrides
Oxidation state of chlorine? Are there any exceptions to this?
-1 - except when with O or F
What is the sum of oxidation states of all elements in a compound?
Zero
What is the sum of the oxidation states of elements in a polyatomic ion equal to?
The charge on the ion
Why is oxygen’s oxidation number not -2 when combined with F?
F is more electronegative
What is the oxidation number of S in H₂SO₄?
+6
What can oxidation states be used to determine?
What has been oxidised and reduced in a reaction (therefore oxidising and reducing agents)
What does it mean if the oxidation state of an element increases?
It has been oxidised
What does it mean if the oxidation state of an element decreases?
It has been reduced
When is a reaction not redox?
When there is no change in oxidation state in a reaction
What is a disproportionation reaction?
A redox reaction in which the same substance is both oxidised and reduced
Which substances can be split into ions for half equations?
Ionic substances only
What happens to polyatomic ions in half equations?
They are not split up into individual element
What balances oxygen in half equations?
Water
What balances excess hydrogen from water in half equations?
H+ ions
In overall redox equations, what needs to be cancelled out?
Electrons
How are overall redox equations formed?
By adding the two half equations together - after ensuring the number of electrons are equal (and therefore cancel)
