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TechnoratiImportant Reactions with Metals (Half Reactions/Ionic equati
Submitted by Anonymous on 22 April 2005 - 6:30am.
Hi I really dont understand half reactions like is it always 2E+ or 2E- how do you know. Here are some sample questions
1. Write
a) Balanced chemical equations and b)ionic equations
for i)Calcium metal and water ii)zinc and hydrochloric acid
I can do part a but not b how do you work out part b
My Answers
i) a) Ca(s) + 2H2O(l) -> Ca(OH)2 (aq) + H2(g)
b)
ii) a) Zn(s)+2HCl(aq) -> ZnCL2(aq) + H2 (g)
b)
Thanks heaps sincerly
Nathan
First, you need to find the oxidation numbers for everything. Then, you can tell what gets reduced and what gets oxidized. From there, right the half reactions, then multiply to get the number of elections equal in each half reaction, then add. If you did it right, the e-'s should disappear.
oxidation numbers
how od you find the find the oxidation numbers
The oxidation number of an atom in an elementary substance is 0. This means that the oxidation number of an O atom in O2 is 0.
The oxidation number of a Group IA atom in any compund is
+1; The oxidation number of a Group IIA atom in any compund is +2.
The oxidation number of fluorine is -1 in all of its compounds.
The oxidation number of chlorine, bromine, and iodine is -1 in any compound containing only two elements.
The usual oxidation number of oxygen in a compound is -2. The major exceptions of this rule are peroxides, like H2O2, which have an oxidation number of -1.
The oxidation number of hydrogen in most compounds is +1.
The sum of the oxidation numbers in a compound is always zero. For something that is an ion consisting of two atoms (a polyatomic ion), the oxidation numbers add up to the charge on the ion.
Example: *LiF* Ox#Li=+1 Ox#F=-1
Basically, use the rules above to find one of the ox numbers, then it's just simple math to find the other.
thanks
thanks for your help