Question

Oxidation states are important for keeping track of electrons in oxidation-reduction reactions. Here are some general rules to remember:

In most cases, oxygen has an oxidation state of −2.

Group 1 and group 2 elements on the periodic table have +1 and +2 oxidation states, respectively.

In most cases, hydrogen has an oxidation state of +1.

Many elements can have more than one oxidation state. In such cases, use the other elements in the compound whose oxidation states are known to determine the oxidation state of the element that varies.

Neutral compounds In a neutral compound, the sum of the oxidation states is zero. Note that the sign of the oxidation states and the number of atoms associated with each oxidation state must be considered. In H2O, for example, each hydrogen atom has an oxidation state of +1 and each oxygen atom has an oxidation state of −2 for a total of 2(+1)+(−2)=0.

Part A) What is the oxidation state of an individual carbon atom in CaCO3?

Express the oxidation state numerically (e.g., +1).

Part B) What is the oxidation state of an individual nitrogen atom in KNO3?

Express the oxidation state numerically (e.g., +1).

In an ion, the sum of the oxidation states is equal to the overall ionic charge. Note that the sign of the oxidation states and the number of atoms associated with each oxidation state must be considered. In OH−, for example, the oxygen atom has an oxidation state of −2 and the hydrogen atom has an oxidation state of +1, for a total of (−2)+(+1)=−1.

Part C) What is the oxidation state of an individual phosphorus atom in PO33−?

Express the oxidation state numerically (e.g., +1).

Answer 1

Part A) CaCO₃

Calcium carbonate is a neutral molecule where calcium (Ca²⁺)ishavingan oxidation number of +2 & carbonate (CO₃^2-) is having the oxidation state of -2.

To calculate the oxidation state of carbon we need to consider the carbonate ion,

For carbonate, we know oxygen has to be -2 and there are 3 oxygen atoms. We also know that carbonate has a -2 charge.

If the oxidation number of carbon is x,

then, x + ((-2)×3) = -2.

x=-2 + 6 = 4

Hence, carbon is having an oxidation number of +4

Part B) KNO₃

Potassium nitrate is composed of two ions, K+ and NO₃^-.

K+ means the oxidation number for potassium is +1 since the net charge is +1.

We know that oxidation number for oxygen is -2 in most of the cases (except in certain examples as peroxides and superoxides).

And the net charge for NO₃^- is -1,

If the oxidation number of nitrogen is x,

then, x + ((-2)×3) = -1.

x=-1 + 6 = 5

Hence, nitrogen is having an oxidation number of +5

Part C) PO₃^3-

The net charge on this ion is -3.

& we know that oxygen is having the oxidation number of -2

If the oxidation number of phosphorus is x

then, x + ((-2)×3) = -3.

x=-3 + 6 = 3

Hence, phosphorus is having an oxidation number of +3