The oxidation state of S in Na2S2O3 is
The oxidation state of S in Na2S2O3 is
The correct options are
A +5
B -1
The Sodium parts of the compound exist as Na+ ions. So let us look at the structure of the thiosulphate ion S2O2−3 :
Let us look at how IUPAC defines “oxidation state”. Oxidation State is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules:
1. The oxidation state of a free element (uncombined element) is zero;
2. For a simple monatomic ion, the oxidation state is equal to the net charge on the ion;
3. In general, for most chemical compounds, Hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2. (Notable exceptions to this rule are that hydrogen has an oxidation state of -1 in hydrides of active metals, e.g. NaH, and oxygen has an oxidation state of -1 in peroxides, e.g. Na2O2);
4. In a neutral molecule, the algebraic sum of oxidation states of all atoms must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion.
Without violating the IUPAC rules, we could attribute any of the following combinations of oxidation states:
O.S of Peripheral S atomO.S. of Central S atomAverage O.S−2+6+2−1+5+20+4+2
According to the expanded definition of Oxidation state, the last combination is more appropriate. Equally valid is the -1,+5 formal assignment.
A
+5
B
-1
The Sodium parts of the compound exist as Na+ ions. So let us look at the structure of the thiosulphate ion S2O2−3 :
Let us look at how IUPAC defines “oxidation state”. Oxidation State is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules:
1. The oxidation state of a free element (uncombined element) is zero;
2. For a simple monatomic ion, the oxidation state is equal to the net charge on the ion;
3. In general, for most chemical compounds, Hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2. (Notable exceptions to this rule are that hydrogen has an oxidation state of -1 in hydrides of active metals, e.g. NaH, and oxygen has an oxidation state of -1 in peroxides, e.g. Na2O2);
4. In a neutral molecule, the algebraic sum of oxidation states of all atoms must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion.
Without violating the IUPAC rules, we could attribute any of the following combinations of oxidation states:
O.S of Peripheral S atomO.S. of Central S atomAverage O.S−2+6+2−1+5+20+4+2
According to the expanded definition of Oxidation state, the last combination is more appropriate. Equally valid is the -1,+5 formal assignment.
