Question

You are asked to identify compound X (a white, crystalline solid), which was extracted from a plant seized by customs inspectors. An elemental analysis of X shows that the mass percentage composition of the compound is 26.86% C and 2.239% H, with the remainder being oxygen. A mass spectrum of X yields a molar mass of 90.0 g/mol. Write the molecular formula of X.

Answer 1

C2H2O4

Step-by-step explanation:

To get the molecular formula, we first get the empirical formula. This can be done by dividing the percentage compositions by the atomic masses. The percentage compositions are shown as follows :

C = 26.86%

H = 2.239%

O = 100 - ( 26.86 + 2.239) = 70.901%

We then proceed to divide by their atomic masses. Atomic mass of carbon is 12 a.m.u , H = 1 a.m.u , O = 16 a.m.u

The division is as follows:

C = 26.86/12 = 2.2383

H = 2.239/1 = 2.239

O = 70.901/16 = 4.4313

We now divide each by the smallest number I.e 2.2383

C = 2.2383/2.2383 = 1

H = 2.239/2.2383 = 1

O = 4.4313/2.2383 = 1.98 = 2

Thus, the empirical formula is CHO2.

To get the molecular formula, we use the molar mass .

(CHO2)n = 90

We add the atomic masses multiplied by n.

(12 + 1 + 2(16))n = 90

45n = 90

n = 90/45 = 2.

Thus , the molecular formula is C2H2O4