9.1 Flashcards
(29 cards)
Oxidation
Old definition: gain of oxygen; loss of hydrogen
New definition: loss of electron
Reduction
Old definition: loss of oxygen; gain of hydrogen
New definition: gain of electron
Oxidation state
value we assign to each atom in a compound that is a measure of control or possession it has relative to the atom in the pure element
atoms in the free (uncombined) element have an oxidation state of
zero
In simple ions, the oxidation state is
the same as the charge of the ion
the oxidation states of all the atoms in a neutral (uncharged) compound must add up to
zero
the oxidation states of all the atoms in a polyatomic ion must add up to
the charge of the ion
the usual oxidation state for an element is
the same as the charge on its most common ion
most of which elements have oxidation states that vary in different compounds
Main group non metals; the elements at the bottom of Group 14 and transition elements
Usual oxidation state of Li, Na, K
+1
Usual oxidation state of Mg, Ca
+2
Usual oxidation state of F
-1; no exceptions because F is the most electronegative element
Usual oxidation state of O
-2
Exceptions are
peroxides such as H2O2 where it is -1
OF2 where it is +2
Usual oxidation state of H
+1
Exceptions are metal hydrides such as NaH where it is -1, this is due toe the fact that H is more electronegative that Na so it gains electron control
Usual oxidation state of Cl
-1
exceptions are when it is combined with O or F because Cl is less electronegative that O and F so it loses electron control
redox reaction
chemical reaction in which changes in the oxidation states occur
Oxidation occurs when there is
an increase in oxidation state of an element
Reduction occurs when there is
a decrease in oxidation state of an element
Half equations
redox equation separated into equations for the oxidation and reduction processes
summary of steps in writing redox equations
- Assign oxidation states to determine which atoms are being oxidized and which are being reduced
- Write half equations for oxidation and reduction as follows:
a.balance the atoms other than H and O
b.Balance each half equation for O by adding H2O as needed
c. balance each half equation for H by adding H+ as needed
d. balance each half equation for charge by adding electrons to the sides with the more positive charge
e. check that each half equation is balanced for atoms and for charge - equalize the number of electronc in the two half equations by multiplying each appropriately
- add the two half equations together, cancelling out anything that is the same on both sides.
Oxidizing agent
substance that is being reduced
reducing agent
substance that is being oxidized
more reactive metals are
stronger reducing agents
more reactive metal is able to
reduce the ions of a less reactive metal
