Mercury can be obtained by reacting mercury(II) sulfide with
calcium oxide. How many grams of mercury(II) sulfide are
needed to produce 26.0 g of Cas?
4HgS(s) + 4CaO(s) — 411g() + 3CaS(s) + Caso.

111.68 g

Explanation:

Given data:

Mass of HgS needed = ?

Mass of CaS produced = 26.0 g

Solution:

Chemical equation;

4HgS + 4CaO  →     4Hg + 3CaS + CaSO₄

Number of moles of CaS:

Number of moles = mass/molar mass

Number of moles = 26 g/ 72.143 g/mol

Number of moles = 0.36 mol

Now we will compare the moles of HgS with CaS.

                 CaS             :             HgS

                   3                :               4

                   0.36           :              4/3×0.36 = 0.48 mol

Mass of HgS:

Mass = number of moles × molar mass

Mass = 0.48 mol × 232.66 g/mol

Mass = 111.68 g

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.