How many grams of magnesium oxide are formed if 20.9 grams of Mg and 15.2 g of O2 react.

Mass of magnesium oxide formed = 35.1 g

Explanation:

Given data:

Mass of Mg = 20.9 g

Mass of O₂ = 15.2 g

Mass of magnesium oxide formed = ?

Solution:

Chemical equation:

2Mg + O₂     →   2MgO

Number of moles of Mg:

Number of moles = mass/molar mass

Number of moles = 20.9 g/ 24 g/mol

Number of moles = 0.87 mol

Number of moles of O₂:

Number of moles = mass/molar mass

Number of moles = 15.2 g/ 32 g/mol

Number of moles = 0.475 mol

Now we will compare the moles of MgO with magnesium and oxygen.

                Mg          :         MgO

                  2           :           2

                0.87        :         0.87

                  O₂         :         MgO

                     1         :            2

                   0.475   :        2/1×0.475 = 0.95  

Number of moles of MgO formed by Mg are less thus Mg will limiting reactant.

Mass of MgO:

Mass = number of moles × molar mass

Mass = 0.87 mol × 40.3 g/mol

Mass = 35.1 g

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."