200g of solution of magnesium
chloride is reacted with 20g caustic soda
(NaOH). (Mg =24, Cl =35.5, Na =23, 0 = 16, H
=1)

A) Find the mass of the reacted
magnesium chloride
B) Find the percent by mass of solution magnesium chloride.
C) Find the mass of the obtained solid.

Respuesta :

The mass of reacted magnesium chloride is 23.75g, percent by mass of solution magnesium chloride is 90.9%.

What is the relation between mass & moles?

Relation between the mass and moles of any substance will be represented as:

n = W/M, where

  • W = given mass
  • M = molar mass

Moles of MgCl₂ = 200g / 95g/mol = 2.1mol

Moles of NaOH = 20g / 0.5mol

Given chemical reaction is:

MgCl₂ + 2NaOH → 2NaCl + Mg(OH)₂

From the stoichiometry of the reaction it is clear that

  • 1 mole of MgCl₂ = reacts with 2 moles of NaOH
  • 0.5 mole of NaOH = reacts with (1/2)(0.5)=0.25 moles of MgCl₂

Mass of reacted MgCl₂ = (0.25mol)(95g/mol) = 23.75g

Percent by mass of MgCl₂ in the given solution mixture will be calculated as:

  • % by mass = (Mass of MgCl₂ / Total mass of mixture) × 100%
  • Percent by mass of MgCl₂ = (200/200+20)×100% = 90.0&

In the above reaction we obtain NaCl as a solid, and MgCl₂ is the limiting reagent in it, from which 2 moles of NaCl is produced means

  • 0.25 moles of MgCl₂ = produces 0.5 moles of NaCl

Mass of NaCl = (0.5mol)(58.5g/mol) = 29.25g

Hence, mass of reacted MgCl₂ is 23.75g, percent by mass of solution magnesium chloride is 90.9% and mass of the obtained solid is 29.25g.

To know more about mass & moles, visit the below link:

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