[Raigar789]

My class is currently on mole conversion problems. The problem I have is this. "the density of aluminum is 2.70g/ml. If aluminum atoms are spherical with a diameter of 2.96x10-8; what percent of any aluminum sample is empty space, unoccupied by atoms?"

I started out by finding the volume of each atom. I divided the diameter by 2 to get 1.48x10-8 as the radius. From there I plugged it in the equation of (4/3)(pie)®3 [3=cubed]. I got a volume of 1.35x10-23 as the volume of the spherical atom of aluminum. From there I decided to place the atom in a cube, then substractthevolumes to get the remaining space as empty space. Using the diameter for each side I got a volume of 2.59x10-23. Using subtraction I get 1.24x10-23. Then that is divided by the whole which is the volume of the cube, to get 48% of empty space, but the answer is 18%.

The second problem is, "Equal moles of aluminum and sodium are converted to their respective oxide compounds If the balloon (STP) holding all the necessary oxygen gas for the conversions, has a volume of 20.0L, what original metal masses were used?"

For this probelm I have no idea where to start. I am not sure what to do with the volume of Oxygen, or what to do at all.

Please help,
Thank you

[Yggdrasil]

My class is currently on mole conversion problems. The problem I have is this. "the density of aluminum is 2.70g/ml. If aluminum atoms are spherical with a diameter of 2.96x10-8; what percent of any aluminum sample is empty space, unoccupied by atoms?"

I started out by finding the volume of each atom. I divided the diameter by 2 to get 1.48x10-8 as the radius. From there I plugged it in the equation of (4/3)(pie)®3 [3=cubed]. I got a volume of 1.35x10-23 as the volume of the spherical atom of aluminum. From there I decided to place the atom in a cube, then substractthevolumes to get the remaining space as empty space. Using the diameter for each side I got a volume of 2.59x10-23. Using subtraction I get 1.24x10-23. Then that is divided by the whole which is the volume of the cube, to get 48% of empty space, but the answer is 18%.

The way you assume the atoms are packed is wrong (spheres pack very differently than cubes).  A better approach would be to find the number of aluminum atoms in 1mL of aluminum (using the density), then calculate the volume taken up by those atoms.

The second problem is, "Equal moles of aluminum and sodium are converted to their respective oxide compounds If the balloon (STP) holding all the necessary oxygen gas for the conversions, has a volume of 20.0L, what original metal masses were used?"

For this probelm I have no idea where to start. I am not sure what to do with the volume of Oxygen, or what to do at all.

How do you start with any chem problem?  Write a balanced chemical reaction.  In this case, find the reaction or the oxidation of Na and Al, in order to find the number of moles of oxygen gas used per mole of Na and Al.

[Raigar789]

I'm sorry for the trouble, but how would I find the number of atoms in a ml? I know how to find the number of atoms in a certain amount of mass, but not ml. I still do not know what to do  . Could you please explain to me?
Thank you

[Yggdrasil]

Use the density of aluminum.  1mL of Al = 2.70g