Question

Elemental analysis of caffeine yields the following results: 49.49% C, 5.15% H, 28.87% N, and the remainder is O. What is the molecular formula of caffeine?

Answer 1

Answer:

The answer to your question is C₄H₅N₂O

Explanation:

Process

1.- Calculate the percent of oxygen in the sample

    Percent of oxygen = 100 - 49.49 - 5.15 - 28.87

    Percent of oxygen = 16.49 %

2.- Write the percents as grams

C = 49.49 g

H = 5.15 g

N = 28.87 g

O = 16.47 g

3.- Convert the grams to moles

C          12 g ------------------- 1 mol

          49.49 g ----------------  x

             x = (49.49 x 1) 12

             x = 4.12 moles

H        1 g -------------------   1 mol

         5.15 g ----------------  x

            x = (5.15 x 1)/ 1

            x = 5.15 moles

N          14 g  --------------- 1 mol

            28.87 g ----------  x

              x = (28.87 x 1) / 14

              x = 2 mol

O           16 g ---------------- 1 mol

              16.49 g ----------- x

               x = (16.49 x 1) / 16

               x = 1.03 moles

4.- Divide by the lowest number of moles

C     4.12 /  1.03 = 4

H      5.15 / 1.03 = 5

N       2 / 1.03 = 1.9 ≈ 2

O      1.03 / 1.03 = 1

5.- Write the empirical formula

                                 C₄H₅N₂O