Respuesta :
Answer:
The empirical formula is = [tex]CH_2O[/tex]
The formula of lactic acid = [tex]C_3H_{6}O_3[/tex]
Explanation:
Corrected from source, empirical formula and molecular formula of the lactic acid is to be determined.
Mass of water obtained = 3.000 g
Molar mass of water = 18 g/mol
Moles of [tex]H_2O[/tex] = 3.000 g /18 g/mol = 0.1667 moles
2 moles of hydrogen atoms are present in 1 mole of water. So,
Moles of H = 2 x 0.1667 = 0.3333 moles
Molar mass of H atom = 1.008 g/mol
Mass of H in molecule = 0.3333 x 1.008 = 0.3359 g
Mass of carbon dioxide obtained = 7.329 g
Molar mass of carbon dioxide = 44.01 g/mol
Moles of [tex]CO_2[/tex] = 7.329 g  /44.01 g/mol = 0.1665 moles
1 mole of carbon atoms are present in 1 mole of carbon dioxide. So,
Moles of C = 0.1665 moles
Molar mass of C atom = 12.0107 g/mol
Mass of C in molecule = 0.1665 x 12.0107 = 2.0001 g
Given that the Lactic acid only contains hydrogen, oxygen and carbon. So,
Mass of O in the sample = Total mass - Mass of C Â - Mass of H
Mass of the sample = 5.000 g
Mass of O in sample = 5.000 - 2.0001 - 0.3359 = 2.6641 g Â
Molar mass of O = 15.999 g/mol
Moles of O Â = 2.6641 / 15.999 Â = 0.1665 moles
Taking the simplest ratio for H, O and C as:
0.3333 : 0.1665 : 0.1665
= 2 : 1 : 1
The empirical formula is = [tex]CH_2O[/tex]
Molecular formulas is the actual number of atoms of each element in the compound while empirical formulas is the simplest or reduced ratio of the elements in the compound.
Thus, Â
Molecular mass = n Ă— Empirical mass
Where, n is any positive number from 1, 2, 3...
Mass from the Empirical formula = 1Ă—12 + 2Ă—1 + 16= 30 g/mol
Molar mass = 90.08 g/mol
So, Â
Molecular mass = n Ă— Empirical mass
90.08 = n Ă— 30
⇒ n = 3
The formula of lactic acid = [tex]C_3H_{6}O_3[/tex]
