Question

1. Mercury is most often obtained by roasting cinnabar (HgS). How many grams of cinnabar
are required to obtain 165 grams of mercury?
HgS + 02—-Hg + SO2

Answer 1

Answer:

191.4 grams of cinnabar  are required to obtain 165 grams of mercury.

Explanation:

The balanced reaction is:

HgS + O₂ ⇒ Hg + SO₂

By reaction stoichiometry, the following amounts of moles of each compound participate in the reaction:

• HgS: 1 mole
• O₂: 1 mole
• Hg: 1 mole
• SO₂: 1 mole

Being the molar mass of each compound:

• HgS: 232g/mole
• O₂: 32 g/mole
• Hg: 200 g/mole
• SO₂: 64 g/mole

the following mass amounts of each compound participate in the reaction:

• HgS: 1 mole* 232 g/mole= 232 g
• O₂: 1 mole* 32 g/mole= 32 g
• Hg: 1 mole* 200 g/mole= 200 g
• SO₂: 1 mole* 64 g/mole= 64 g

Then you can apply the following rule of three: if by stoichiometry 200 grams of Hg are formed from 232 grams of HgS , 165 grams of Hg are formed from how many grams of HgS?

$mass of HgS=\frac{165 grams of Hg*232 grams of HgS}{200 grams of Hg }$

mass of HgS= 191.4 grams

191.4 grams of cinnabar  are required to obtain 165 grams of mercury.