Denitrification is an important process in wastewater treatment plants. In the p

Question

Denitrification is an important process in wastewater treatment plants. In the process, nitrogen is converted from the nitrate ion (NO 3- ) to gaseous nitrogen (N 2 ). The bacteria that carry out this process can use methanol (CH 3 OH) as a food source, converting the carbon to CO 2 , which is also released as a gas. (a) Give the oxidation states of N in NO 3- and in N 2 ? (b) Give the oxidation states of C in CH 3 OH and in CO 2 ? (c) Write a properly balanced chemical reaction that converts nitrate and methanol in water to N 2 and CO 2

Explanation / Answer

A) The oxidation state of N in NO-3 is, +5.

N carries +5 charge and each O carries -2 charge so the total balance becomes + 5 - 6 = -1 which makes the ion negative.

In N2, The oxidation state of N is 0. In fact oxiddation state of any element such as Fe, H2, O2, P4, S8 is zero

B) The oxidation state of C in CH3OH is, -2

oxygen has -2 charge and hydrogen has +1 so the balancing charge in carbon is +2

In CO2,

The carbon has oxidation state +4,

because the oxygen carries -2 charge and there are 2 oxygen molecules.

C)

6NO3- + 5CH3 OH = 3N2 + 5CO2+ 7H2O + 6OH-

Here the basic reaction is,

NO3- + CH3 OH = N2 + CO2+ H2O + OH-

The coefficients are added for balaning Stoichiometry

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