Determine the following to four significant figures:
(a) the percent composition of hydrazoic acid, hn3
(b) the percent composition of tnt, c6h2(ch3)(no2)3
(c) the percent of so42-in al2(so4)3

Explanation:

(a) the percent composition of hydrazoic acid, HN₃

The mass of the atoms are as follows -

mass of H = 1 g/mol

mass of N = 14 g/mol

The percentage of H = mass of hydrogen / mass of total compound * 100

The percentage of H = 1 / ( 1 + 3 * 14 ) * 100 = 2.326 %

The percentage of the remaining N =  100 - 2.326 = 97.67 %

( b ) the percent composition of TNT, C₆H₂(CH₃)(NO₂)₃

The mass of the atoms are as follows -

mass of C = 12 g /mol

mass of H = 1 g /mol

mass of N = 14 g /mol

mass of O = 16 g /mol

Molar mass of TNT is 12 (7) + 1 (5) + 14 (3) + 16 (6) = 229 g/mol

The percentage of H = 5 * 1 / 229 = 2.183 %

The percentage of C = 7* 12 / 229 = 36.68 %

The percentage of N = 3 * 14 / 229 = 18.34 %

The percentage of O = 6 * 16 / 229 = 42.78 %

(c) the percent of SO₄²⁻in Al₂(SO₄)₃

The mass of the atoms are as follows -

mass of O = 16 g /mol

mass of S = 32 g/mol

mass of Al = 27 g/mol

The molar mass of SO₄²⁻ = 32 + 4 * 16 = 96 g/mol

The molar mass of Al₂(SO₄)₃ = 342 g /mol

The percentage of SO₄²⁻in Al₂(SO₄)₃ = 96 g/mol / 342 g /mol * 100 =

28.07 % .

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