Here's my best guess
the volume of the unit cell is (385*10^-12)^3=5.7066*10^-29 m^3
multiply by density to get mass
mass = (7 g/cm^3)*(100^3 cm^3 / 1^3 m^3) * 5.7066*10^-29 m^3= 3.99466*10^-22 g
covert to moles
3.99466*10^-22 g * 1 mol / 239.82 g = 1.6657 *10^-24 mol
convert to number of units
1.6657 *10^-24 mol * 6.23*10^23 units/mol = 1.04
385 pm = 3.85*10^(-8) cm
The volume of the unit cell is the cube of that, which is 5.71*10^(-23) cm^3. Since the ratio of mass to volume (i.e. the density) must be the same no matter what amount of TlCl you have, you can say:
7 = x/(5.71*10^(-23)), where x is the mass of the unit cell. Solving for x, you get 4*10^(-22) g.
The mass of a molecule of TlCl is 240 amu, which in grams is 4*10^(-22) g. The mass of the unit cell and the mass of a molecule of TlCl is the same. Therefore there is one formula unit of TlCl per unit cell.
Answer:
C6H12O6
Explanation:
Just use the table method like I did and compared the molecular mass with the mass of the empirical formula.
To determine the amount of oxygen that is present in the compound, we have to assume that the given compound contains carbon, hydrogen and oxygen only or else we will not be able to determine the answer. We need to convert the moles of the elements given to units of grams by using the atomic mass of these elements. Then, from the total amount of the compound we subtract the masses of the elements. We do as follows:
mass
0.117 mol C ( 12.01 g / 1 mol ) = 1.41 g
0.233 mol H ( 1.01 g / 1 mol ) = 0.24 g
Mass O = 3.50 g - 1.41 g - 0.24 g = 1.85 g O
Moles O = 1.85 g O ( 1 mol / 16 g ) = 0.116 moles O
