Question

How many moles of mercury(II) oxide, HgO, are needed to pro- duce 125 g of oxygen, O2?

Answer 1

Write out the balanced equation:

2HgO ----> 2Hg + O2

Convert grams of O2 to moles:

(125g of O2 * 1 mole)/ 32g of O2 = 3.91

Look at the ratio with HgO to O2:

2:1

Therefore:

3.91 * 2 = 7.82

Answer 2

The number of moles of mercury(II) oxide needed to produce 125 of oxygen is 7.8 moles

The balanced chemical equation for the decomposition of mercury(II) oxide, HgO to produce oxygen is

2HgO(s) → 2Hg(l) + O₂(g)

This means

2 moles of HgO decomposes to produce 1 mole of Oxygen (O₂)

Now, we will determine the required number of moles of oxygen to be produced

Mass of oxygen to be produced = 125 g

From the formula

$Number\ of\ moles = \frac{Mass}{Atomic\ mass}$

Atomic mass of oxygen = 32 g/mol

∴ Number of moles of O₂ to be produced = $\frac{125}{32}$

Number of moles of O₂ to be produced = 3.90625 mol

Now,

Since 2 moles of HgO decomposes to produce 1 mole of Oxygen (O₂)

Then,

2 × 3.90625 moles of HgO decomposes to produce 3.90625 moles of Oxygen (O₂)

2 × 3.90625 = 7.8125 ≅ 7.8 moles

Hence, the number of moles of mercury(II) oxide needed to produce 125 of oxygen is 7.8 moles

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