Iron oxide (feo) has the rock salt crystal structure and a density of 5.70 g/cm3. the atomic weights of iron and oxygen are 55.85 g/mol and 16.00 g/mol, respectively. (a) determine the unit cell edge length

The unit cell edge length is  

Explanation:

NaCl has FCC structure. and so is the FeO.

Number of atom in unit cell of FCC (Z) = 4

Density of FeO=

Edge length = a

Atomic mass of FeO(M) = 55.85 g/mol +16.00 g/mol = 71.85 g/mol

Formula used :  

where,

= density

Z = number of atom in unit cell

M = atomic mass

= Avogadro's number  

a = edge length of unit cell

On substituting all the given values , we will get the value of 'a'.

The unit cell edge length is  

first, consult an activity series chart to determine if al is more reactive than fe. it is, so it will replace the fe. now, one can continue with the problem.

next, make sure you have a correctly balanced equation.

3feo + 2al ==> 3fe + al2o3

now, determine which reactant (feo or al) is in limiting supply.

moles feo present = 125 g x 1 mole/71.8 g = 1.74 moles

moles al present = 25.0 g x 1 mole/26.98 g = 0.927 moles

since from the balanced equation, it take 3 mol feo for every 2 mol al, al will be limiting.

you can determine this simply by dividing moles of each by their coefficient in the balanced equation. for example: 1.74/3 = 0.58 and 0.927/2 = 0.464. al is less, so it is limiting.

finally, using the stoichiometry in the balanced eq. determine mass of fe that can be produced from 0.927 moles of al.

0.927 moles al x 3 moles fe/2 moles al x 55.8 g/mole = 77.6 g