Question

a solution is prepare by glucose + water in which mole fraction of glucose is 0.2 then find out molality


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Answer 1

Answer:

$\bigstar{\bold{Molality=13.8\:m}}$

Explanation:

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

• Mole fraction of glucose = 0.2

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

• Molality of the solution

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

→ We need to first find the number of moles of glucose

→ The mole fraction of glucose is given by the formula

→ Mole fraction of glucose = number of moles of glucose/ Total number of moles of solution.

→ But mole fraction of glucose is already given,

  0.2 = number of moles of glucose/number of moles of solution.

→ Let number of moles of solution be x

  0.2 = number of moles of glucose/x

→ Number of moles of glucose = 0.2 x

→ Mole fraction of water = 1 - number of moles of glucose

  Mole fraction of moles of water = 1 - 0.2

  Mole fraction of water = 0.8

→ But mole fraction of also given as

  Mole fraction of water = Number of moles of water / Total moles of solution.

      0.8 = Number of moles of water/x

→ Number of moles of water = 0.8 x

→ Number of moles of water is also given as

  Number of moles of water = Given mass/Molar mass

→ Molar mass of H₂O = 2 + 16 = 18

→Substituting it,

  Number of moles of water = Given mass/18

  0.8 x = Given mass/18

→ Mass of water = 0.8 x × 18 g

→ Converting it to kg we get,

  Mass of water = 0.8 x × 18 / 1000 kg

→ Molality of solution is given by the equation,

  Molality = number of moles of solute/Mass of solvent in kg

→ Substitute the datas,

  Molality = 0.2 x × 1000/0.8 x × 18

→ Cancelling x on both numerator and denominator,

  Molality = 0.2 × 1000/0.8 × 18

  Molality = 200/14.4

  Molality = 13.8 m

$\boxed{\bold{Molality=13.8\:m}}$

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

→ Number of moles of solute = Given mass/Molar mass

→ Mole fraction = Number of moles/Total number of moles in solution

→ Molality = number of moles of solute/Mass of solvent in kg

→ Molarity = number of moles of solute/Volume of solution in L

 

Answer 2

Answer:

the answer given by moderator is correct