Answer:
a. +6;
b. +5;
c. +3.
Explanation:
Start with elements with well-known oxidation states.
The oxidation state on oxygen O in compounds is mostly -2. Common exceptions include:
- -1 in peroxides and
- positive when oxygen bonds to fluorine.
The oxidation state on group 1 metals (Li, Na, K, etc.) in compounds is mostly +1.
The oxidation state on group 2 metals (Be, Mg, Ca, etc.) in compounds is mostly +2.
Barium Ba is a group 2 metal. The oxidation state on Ba in the compound BaSO₄ is expected to be +2.
The oxidation state on hydrogen H in compounds is mostly +1. The oxidation state on H might be negative when it is bonded to metals.
The oxidation state on halogens (F, Cl, Br, etc.) is mostly -1. The oxidation state may vary when the halogen is bonded to oxygen or another halogen element.
Compounds are neutral. The oxidation state on all atoms in a compound shall add up to 0. Both BaSO₄ and HClO₂ are neutral.
<h3>BaSO₄</h3>
Oxidation states:
- Ba: +2;
- The oxidation state on sulfur S is to be determined;
- O: -2.
Let the oxidation state on S be x.
2 + x + 4 × (-2) = 0;
x = 6.
Hence, the oxidation state on S in BaSO₄ is +6.
<h3>HClO₂</h3>
Oxidation states:
- H: +1;
- Cl here is bonded to oxygen. The oxidation state on chlorine Cl is to be determined;
- O: -2.
Let the oxidation state on Cl be x.
<em>Refer to the equation in BaSO₄ as an example. Try setting up the equation on your own. </em>
x = 3.
Hence, the oxidation state on Cl is +3.
<h3>PO₄³⁻</h3>
Ions carry charge. Oxidation states on atoms in an ion shall add up to the charge of the ion. The superscript of an ion shows its charge. The superscript 3- in the phosphate ion shows that the ion carries a charge of -3.
Oxidation states:
- The oxidation state on P is to be found;
- O: -2.
Let the oxidation state on P be x.
x + 4 × (-2) = -3;
x = 5.
Hence, the oxidation state on P is +5.
