Question

What is the empirical formula of the compound? Its molar mass is 294.18 g/mol. What is the molecular formula of the compound?

Please solve the whole question a and b. both of them are one question.

Answer 1

The compound has

26.58% Potassium

35.35% Chromium

38.07% Oxygen

a) For the imperical formula of the compound be K_xCr_yO_z

The atomic weight of potassium is 39

Chromium is 52

Oxygen is 16

molecular weight of the compound is (39x + 52y + 16z)

for potassium being 26.58% = 39x / (39x + 52y + 16z)

x = 6.81*10-3 *  (39x + 52y + 16z)

for chromium being 35.35% = 52y /  (39x + 52y + 16z)

y = 6.8*10-3 *  (39x + 52y + 16z)

for oxygen being 38.07% = 16z /  (39x + 52y + 16z)

z = 23.8*10-3 *  (39x + 52y + 16z)

Now by taking the ratio we get

x:y:z = [6.81*10-3 *  (39x + 52y + 16z)] :[ 6.8*10-3 *  (39x + 52y + 16z)] : [23.8*10-3 *  (39x + 52y + 16z)]

which can be reduced to

x:y:z = 1:1: 3.5

Hence the imperical formula for the given compound is  K₁Cr₁O_3.5

b)

the molar mass of the compound is 294.18 g/mol

For the molecular formula of the compound be K_aCr_bO_c

The atomic weight of potassium is 39

Chromium is 52

Oxygen is 16

molecular weight of the compound is (39a + 52b + 16c) = 294.18 g/mol

for potassium being 26.58% = 39a / (39a + 52b + 16c) = 39a/294.18 = 0.13a

a = 2

for chromium being 35.35% = 52b / (39a + 52b + 16c) = 0.18 b

b = 2

for oxygen being 38.07% = 16c / (39a + 52b + 16c) = 0.054c

c = 7

Hence the molecular formula for the given compound is  K₂Cr₂O₇