a 0.784 g sample of magnesium is added to a 250 ml flask and dissolved in 150ml of water. magnesium hydroxide obtained from the reaction required 215.0 mL of 0.300 M hydrochloric acid to completely react. How many moles of Mg were used?

Respuesta :

The chemical reaction involving Mg(OH)2 and HCl is:

Mg(OH)2  +  2HCl  -->  MgCl2  +  2H2O

 

So we see that for every 2 moles of HCl, 1 mole of Mg is reacted.

Calculating for moles HCl:

moles HCl = 0.300 M * 0.215 L

moles HCl = 0.0645 mol

 

The moles Mg then is:

moles Mg = 0.0645 mol * (1 / 2)

moles Mg = 0.03225 mol

0.03255 moles of Mg is used for neutralizing 0.3 M 245 ml [tex]\rm Mg(OH)_2[/tex].

The chemical reaction of the reaction of Mg with water yields Magnesium hydroxide.

The neutralization reaction of [tex]\rm Mg(OH)_2[/tex] with HCl will be:

[tex]\rm Mg(OH)_2\;+\;2\;HCl\;\rightarrow\;MgCl_2\;+2\;H_2O[/tex]

For neutralizing 1 mole of magnesium hydroxide 2 moles of HCl are required.

The moles  of HCl in the question are:

moles = [tex]\rm molarity\;\times\;\dfrac{1000}{Volume\;(ml)}[/tex]

moles of HCl = 0.3 [tex]\rm \times\;\dfrac{1000}{215}[/tex]

moles of HCl = 0.0645 moles.

The moles of Mg required are half of HCl.

Moles of Mg = [tex]\rm \dfrac{0.0645}{2}[/tex]

Moles of Mg = 0.03225.

0.03255 moles of Mg is used for neutralizing 0.3 M 245 ml [tex]\rm Mg(OH)_2[/tex].

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