Question

Calculate the percent, by weight, of carbon in 154 g of C4H8O3?
(C=12, H=1, O=16)

a. 72%
b. 46%
c. 31%
d. 27%
e. 55%​

Answer 1

we have to find the percent by weight of carbon in 154g of C₄H₈O₃.

solution : given weight of  C₄H₈O₃ = 154 g

molecular weight of  C₄H₈O₃ = 4 × atomic weight of C + 8 × atomic weight of H + 3 ×  atomic weight of O

= 4 × 12 + 8 × 1 + 3 × 16

= 48 + 8 + 48

= 104 g/mol

now the number of moles of  C₄H₈O₃ = given mass/molecular mass of C₄H₈O₃

= 154/104 = 1.48 mol

so the number of moles of C = 4 × no of moles of  C₄H₈O₃

= 4 × 1.48 mol

= 5.92 mol

∴ mass of carbon in 154 g of  C₄H₈O₃ = 5.92 × 12 = 71.04 g

now the percent by weight of carbon = mass of carbon/molecular mass of  C₄H₈O₃ = 71.04/154 × 100 ≈ 46 %

therefore the percent by weight of carbon in 154g of  C₄H₈O₃ is 46%.