The amount of nitrogen in an organic substance can be determined by an analytica

Question

The amount of nitrogen in an organic substance can be determined by an analytical method called the Kjeldahl method, in which all the nitrogen in the organic substance is converted to ammonia. The ammonia, which is a weak base, can be neutralized with hydrochloric acid, as described by the equation NH3(aq) + HCl(aq) NH,CI(aq) If 74.0 mL of 0.150 M HCI(aq) is needed to neutralize all the NHs(g) from a 2.25-g sample of organic material, calculate the mass percentage of nitrogen in the sample. Number

Explanation / Answer

we have the Balanced chemical equation as:

HCl + NH3 ---> NH4Cl

lets calculate the mol of HCl

volume , V = 74.0 mL

= 7.4*10^-2 L

we have below equation to be used:

number of mol,

n = Molarity * Volume

= 0.15*0.074

= 1.11*10^-2 mol

From balanced chemical reaction, we see that

when 1 mol of HCl reacts, 1 mol of NH3 reacts

mol of NH3 reacted = (1/1)* moles of HCl

= (1/1)*1.11*10^-2

= 1.11*10^-2 mol

This is number of moles of NH3

Molar mass of NH3 = 1*MM(N) + 3*MM(H)

= 1*14.01 + 3*1.008

= 17.034 g/mol

we have below equation to be used:

mass of NH3,

m = number of mol * molar mass

= 1.11*10^-2 mol * 17.034 g/mol

= 0.1891 g

mass % of NH3 = mass of NH3*100/mass of sample

= 0.1891*100/2.25

= 8.40 %

Answer: 8.40 %

Feel free to comment below if you have any doubts or if this answer do not work. I will edit it if you let me know

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