Question

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A mass of 37.5 g of mercury (II) oxide is decomposed by heating.
a.How many Moles of mercury (II) oxide are decomposed?
b.How many Grams of oxygen are prepared?

Answer 1

In stoichiometry, it is important to:
-Write and balance the equation.
- Consider ratio of moles, masses or of volumes
- The formula for moles is \[n=\frac{ m }{ Mr }\], where n is mol, m is given mass and Mr is Molecular atomic mass.
Working out this problem, we firstly have \[2Hg_{2}O \rightarrow 4Hg + O_{2}\],A.
they want number of moles and we have to use the aforementioned formula n=37.5/201=0.19mol

B.remember to take account of ratio of moles, Hg2O to O2 are in the ratio of 4:1, meaning oxygen has a fourth of the moles of Hg2O or 0.19/4=0.0475mol
Back to the formula of moles, we are to find the given mass reacted and making m the subject becomes m=n*Mr or 0.0475*(16*2)=1.52g of Oxygen.