Calculate the mass of magnesium oxide produced when 0.645 g of magnesium hydroxide is the is completely decomposed.
mg(oh)2 —> mgo + h2o

0.44g

Explanation:

Given parameters:

Mass of magnesium hydroxide = 0.645g

Solution

The balanced reaction equation is shown below:

                             Mg(OH)₂ → MgO + H₂O

From the equation above, we see that the number of atoms are conserved.

To find the mass of magnesium oxide produced, we find the number moles of the decomposed magnesium hydroxide first:

      Molar mass of Mg(OH)₂ = 24 + 2(16+1) = 58g/mol

Number of moles of Mg(OH)₂ =

                                                  =  

                                                  = 0.011mole

Now, from the balanced equaiton, we know that:

     1 mole of Mg(OH)₂ produces 1 mole of MgO

Therefore, 0.011mole of Mg(OH)₂ will produce 0.011mole of MgO

so mass of MgO = number of moles of MgO x molar mass of MgO

   Molar mass of MgO = 24 + 16 = 40g/mol

     mass of MgO = 0.011 x 40 = 0.44g