General Chemistry 4 Donald McQuarrie Peter A. Rock Ethan Gallogly University Sci

Question

General Chemistry 4 Donald McQuarrie Peter A. Rock Ethan Gallogly University Science Books presented by Sapling Learning 4th Editiorn 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) NH4Cl(aq) If 55.0 mL of 0.150 M HCI(aq) is needed to neutralize all the NH3(g) from a 2.25-g sample of organic material, calculate the mass percentage of nitrogen in the sample. Number 8 Hint Previous Give Up & View Solution e Check Answer Next Exit Start by finding the number of moles of HCI. There is a 1:1:1 mole ratio of HCI to NH3 to N.

Explanation / Answer

m = 2.25 g of sample

M = 0.15 HCl

V = 55 ml

find moles of HCl

mol = M*V = 55*.15 = 8.25 mmol of HCl

then since ratio is 1:1, expect 8.25 mmol of NH3

then 8.25 mmol of N are there also

mass of N = 8.25*14 = 115.5*10^-3 g of N

% mass = mass N / MT = (115.5*10^-3)/(2.25) *100 = 5.133 %

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