Question

Chromium is most commonly mined in the form of chromite, which has the chemical formula fecr2o4. calculate the percent by mass of each element in chromite, and give your answers to four significant digits.

Answer 1

 The   mass  of each  elements   in  chromite is as below

Fe  =24.9 %

Cr  =46.5%

O = 28.6%

calculation

percent  mass  =  atomic mass  of  element / atomic mass of FeCr2O4 x 100

from  periodic table  the atomic mass  for  Fe  = 55.85 g/mol,

Cr =52 g/mol  since  they  are two  atoms  in FeCr2O4 =  2 x 52 = 104 g/mol

for  O  = 16   since  they are two  atoms in FeCr2O4 =  16  x4  =  64  g/mol

Atomic mass for  FeCr2O4  is  = 55.85 +104+  64  = 223.85  g/mol

Percent  mass  for Fe  =55.85 /223.85  x100  = 24.9 %

                          for  Cr =  104 / 223.85  x 100  = 46.5%

                           For 0  =  64/223.85  x 100  =  28.6%

Answer 2

Fe atomic mass = 55.86 * 1 = 55.86 Cr atomic mass = 52 *2 = 104 O atomic mass = 16 * 4 = 64 Total molecular mass = 223.86 Percent by mass Fe = (55.86/223.86)*100 = 24.95% Percent by mass Cr = 46.45% Percent by mass O = 28.59%