A0.784 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?

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 .

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

The neutralization reaction of with HCl will be:

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

The moles  of HCl in the question are:

moles =

moles of HCl = 0.3

moles of HCl = 0.0645 moles.

The moles of Mg required are half of HCl.

Moles of Mg =

Moles of Mg = 0.03225.

0.03255 moles of Mg is used for neutralizing 0.3 M 245 ml .

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answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.