Chemistry help needed for balancing equation?

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matsci0000

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Balance the chemical equation by Ion electron method:
Please write the half equations ;
Br -1 +BrO3 -1 + H + ------> Br2+H2O

Balance by oxidation number method:
FeCr2O4+Na2CO3+O2 ---->Fe2O3+Na2CrO4+CO2
 
The question is very simple and a good chem student mus t be able to solve it. But im not one sorry!!!
 
Br -1 +BrO3 -1 + H + ------> Br2+H2O

Br -1 +BrO3 -1 + H + = Br2+H2O

Answer should be 5Br-1 + BrO3-1 + 6H+ = 3Br2 + 3H2O

FeCr2O4+Na2CO3+O2 ---->Fe2O3+Na2CrO4+CO2

8 Na2CO3 + 7 O2 + 4 FeCr2O4 ==> 2 Fe2O3 + 8 CO2 + 8 Na2CrO4
 
in the brackets are oxidation number

2Br(-1) ---> Br2 + 2e | x5
2Br(+5) + 10e ---> Br2 | x1

since only the oxidation number of Br change in the reaction

10[Br(-1)]- + 2[Br(+5)O3]- + 6[H]+ ---> 6Br(0)2 + 6H2O

H+ only appear to equal the number of hydrogen atom


----------------------------------------------------------------------------------------------

2Fe(+2) ---> 2Fe(+3) + 2e | x2
4Cr(+3) ---> 4Cr(+6) + 12e | x2
O2 + 4e ---> 4O(-2) | x7

so

4FeCr2O4 + 8Na2CO3 + 7O2 ---> 2Fe2O3 + 8Na2CrO4 + 8CO2

tricky, i almost get it wrong here ^_^
remember, FeCr2O4 exist as an molecule, so the number of Cr(+3) must be twice that of Fe(+2). thus each FeCr2O4 gives 14 electrons when being oxidized.
 
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