Question

What is the percent composition (by mass) of hydrogen in C2H5NH2?

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Question 38 pts
What is the percent composition (by mass) of sulfur in H2SO4?

Answer 1

Use atomic masses (approx.): H = 1.008, C = 12.011, N = 14.007, S = 32.06, O = 15.999.

1) C2H5NH2 (same as C2H7N)
- Molar mass = 2(12.011) + 7(1.008) + 14.007 = 24.022 + 7.056 + 14.007 = 45.085 g·mol⁻¹
- Mass of H = 7(1.008) = 7.056 g·mol⁻¹
- %H = (7.056 / 45.085) × 100 = 15.66%

2) H2SO4
- Molar mass = 2(1.008) + 32.06 + 4(15.999) = 2.016 + 32.06 + 63.996 = 98.072 g·mol⁻¹
- Mass of S = 32.06 g·mol⁻¹
- %S = (32.06 / 98.072) × 100 = 32.69%

Answers: %H in C2H5NH2 ≈ 15.66%; %S in H2SO4 ≈ 32.69%.