Question

A compound contain 36.5% Na, 25.4% S and 38.1% 0. Calculate the molecular formula if its molar mass is 126u.​

Answer 1

Answer:

$Na_{2}SO_{3}$

Explanation

element -- % age -- %age/ at.mass -- whole ratio

   Na            36.5           1.58                    2

    S             25.4            0.79                   1

   O              38.1            2.38                   3

therefore, ratio of Na,S,O is 2:1:3

               => $Na_{2}SO_{3}$ is the empirical formula

          MW of empirical formula is = 46 + 32 + 48

                                                        = 126

                       

                           → molecular formula  =  $Na_{2}SO_{3}$

Answer 2

Answer:

$\bigstar{\bold{Molecular\:formula=Na_2SO_3}}$

Explanation:

$\Large{\underline{\underline{\bf{Given:}}}}$

• Na = 36.5 g
• S = 25.4 g
• O = 38.1 g
• Molar mass = 126 u =126 g

$\Large{\underline{\underline{\bf{To\:Find:}}}}$

• Molecular formula

$\Large{\underline{\underline{\bf{Solution:}}}}$

→ First we have to find the simplest whole number ratio of all the elements.

→ Element = Na

  Given mass = 36.5 g

  Number of moles = Given mass/Molar mass

  Number of moles of Na = 36.5/23

  Number of moles of Na = 1.59 moles

→ Element = S

  Given mass = 25.4 g

  Number of moles of S = 25.4/32

  Number of moles of S = 0.8 moles

→ Element = O

  Given mass = 38.1 g

  Number of moles of O = 38.1/16

  Number of moles of O = 2.38

→ Simplest Whole number ratio of the elements is given by

  Whole number ratio of Na = 1.59/0.8

  Whole number ratio of Na = 2

  Whole number ratio of S = 0.8/0.8

  Whole number ratio of S = 1

  Whole number ratio of O = 2.38/0.8

  Whole number ratio of O = 3

→ Therefore the empirical formula of the compound = Na₂SO₃

→ Now we have to find the molecular mass of the compound

  Molecular mass of Na₂SO₃ = 23 × 2 + 32 + 16 × 3

  Molecular mass of Na₂SO₃ = 46 + 32 + 48

  Molecular mass of Na₂SO₃ = 126

→ n = Molar mass/Molecular mass

  n = 126/126

  n = 1

→ Molecular formula is given by,

  Molecular formula = n × Empirical formula

→ Substituting the datas,

  Molecular formula = 1 × Na₂SO₃

  Molecular formula = Na₂SO₃

$\boxed{\bold{Molecular\:formula=Na_2SO_3}}$