Calculate the mass fractions of each element in the following compounds a) MgO b) CO2 h) Al2O3 k) KMnO4.

The mass fraction of an individual element that is part of the compound is calculated as follows:

w% (element) = Mr (element): Mr (substance) * 100%.

Using this formula, we find the mass fractions of elements in the composition of the given substances:

a) MgO:

w% (Mg) = Mr (Mg): Mr (MgO) * 100% = 24: 40 * 100% = 60%,

then oxygen accounts for 100% – 60% = 40%

b) CO2:

w% (O) = (2 * 16): Mr (CO2) * 100% = (2 * 16): 44 * 100% = ~ 72.7%,

then the share of carbon accounts for 100% – 72.7% = 27.3%.

c) Al2O3:

w% (Al) = (2 * 27): 102 * 100% = 53%,

then oxygen accounts for 100% – 53% = 47%.

d) KMnO4:

w% (K) = 39: 158 * 100% = 24.7%

w% (Mn) = 55: 158 * 100% = 34.8%,

then oxygen accounts for 100% – (24.7% + 34.8%) = 100% – 59.5% = 40.5%.