I need help in this problems...!!

[pacific]

You would like to be able to physically separate different materials in a scrap

recycling plant. Describe some possible method that might be used to separate materials such as polymers, aluminum alloys, and steel from one another.

 

 

An optical fiber for telecommunication is made of SiO2 glass (density= 2.20

Mg/m3). How many Si atoms and how many O atoms are present per millimeter of length of a fiber 10 micrometer in diameter?

 

 

Make an accurate plot of FA versus r for an Mg2+ - O2- pair. Conceder the range of r from 0.2 to 0.7 nm.

 

 

Describe the quantum number for each of the 11 electrons in sodium.

 

 

If the attractive force between a pair of Mg2+ and S2- ions is 1.49x10-8 N and if the S2- ion has radius of 0.184, calculate a value for the ionic radius of the Mg2+ ion in nanometer.

 

 

The lattice constant for BCC tantalum at 20 oC is 0.3302 nm and its density is 16.6 g/cm3. Calculate a value for its atomic mass.

 

 

Cobalt has an HCP crystal structure, an atomic radius of 0.1253 nm, and a c/a ratio of 1.623. Compute the volume of the unit cell for Co.

 

 

 

Niobium has an atomic radius of 0.1430 nm and a density of 8.57 g/cm3. Determine whether it has an FCC or BCC crystal structure.

 

 

 

 

 

 

BCC = Body-Centered Cubic

FCC = Face-Centered Cubic

HCP = Hexagonal Close-Packed

 

:eek:

[pacific]

i have done 1st,2nd,3rd & 4th....but not sure from 2nd & 3rd...

please if u can solve them note me ... my email is : almosila@hotmail.com

[RyanJ]

At what level are those questions set? If your looking for a site where you'll find the answers I'll point you to the one I use (Have read the whole site a few times) http://www.chemguide.co.uk/

 

I'd like to help more but I am no chemistry expert, maybe one of the resident experts can help you better than I

 

Cheers & Good luck.

 

Ryan Jones

[P-man]

Hmmmm, these are tricky... Gimme some more time.

[woelen]

I do not like this kind of questions. Do you want us to make your home work? I'll give you some hints, but please, next time, show that you've put some effort in the questions yourself.

 

You would like to be able to physically separate different materials in a scrap

recycling plant. Describe some possible method that might be used to separate materials such as polymers' date=' aluminum alloys, and steel from one another.[/quote']

Steel --> magnetic

polymers ---> solvents?

remaining stuff: aluminium alloys

 

 

An optical fiber for telecommunication is made of SiO2 glass (density= 2.20

Mg/m3). How many Si atoms and how many O atoms are present per millimeter of length of a fiber 10 micrometer in diameter?

Compute volume of 1 mm of fiber. I assume you know how to compute the volume of a cylinder with known height and radius.

Volume*density--> mass.

MW(SiO2) gives mass per mole of molecules.

Now you can compute total number of molecules of SiO2 and that gives you the number of O-atoms.

 

 

Make an accurate plot of FA versus r for an Mg2+ - O2- pair. Conceder the range of r from 0.2 to 0.7 nm.

FA? You mean force of attraction?

Radius r is much larger than size of ions. This allows point-charge computations. Use F=k*c1*c2/(r*r), where c1 and c2 are charge and k is a well-known constant (I assume you know that or can find out).

 

 

Describe the quantum number for each of the 11 electrons in sodium.

Quantum numbers are as follows:

principal quantum number, which determines the size of the orbital (the shell number).

angular quantum number, which determines how the orbital looks like (0 = spherical, s; 1 = two lobes, p; 2 = four lobes, d; 3 = even more complex , f). The larger the shell, the more possible shapes there are for orbitals. Please lookup yourself what relation there is (it is simple, I promise you )

magnetic quantum number, which tells you how an orbital is oriented in space. A spherical orbital can only have one magnetic quantum number, it does not matter how it is oriented and hence, each shell has just one s-orbital, but a two-lobes orbital can have three different orientations, perpendicular to each other, so there are three possible p-orbitals per shell.

Finally, electrons have spin, which can be -1/2 or +1/2. In one orbital two electrons can exist, but only of opposite spin.

Now it is your challenge to enumerate all 11 electrons in sodium, telling their principal quantum number, angular quantum number and magnetic quantum number. The spin of all electrons also can be determined, except for one.

Beware, for one electron you must make the assumption that the atom is isolated, otherwise (in real metallic sodium), you have one electron per atom in a conduction band and cannot simply speak of an atomic orbital. It is up to you to decide which atom is doing such nasty things . All other 10 electrons are nice to you and are well-behaved .

 

 

If the attractive force between a pair of Mg2+ and S2- ions is 1.49x10-8 N and if the S2- ion has radius of 0.184, calculate a value for the ionic radius of the Mg2+ ion in nanometer.

Use electrostatic formula, which I have given before. Now you can compute the distance between the two point charges. If you are not allowed to make the simplification that the ions are point charges, then things become MUCH more complex. I cannot deduce from here, however, whether you need to perform that more complex computation. Using the distance between the two point charges and the radius of the S(2-) ion, you can compute the radius of the Mg(2+) ion.

 

 

The lattice constant for BCC tantalum at 20 oC is 0.3302 nm and its density is 16.6 g/cm3. Calculate a value for its atomic mass.

A nice geometry question.

Proceed as follows:

How many atoms are there in one lattice cell?

You know the size of a single lattice cell and you know it is cubic, so you can compute the volume of a single unit cell.

Now you can compute how many unit cells there are in 1 cm3 and from that you know how many atoms there are in 1 cm3. You know there is 16.6 grams per cm3, so you can compute the mass of one atom and you can convert that to an atomic mass number.

 

 

Cobalt has an HCP crystal structure, an atomic radius of 0.1253 nm, and a c/a ratio of 1.623. Compute the volume of the unit cell for Co.

This is a matter of plain geometry. You know the size of the atom, the c/a ratio tells you something about the size of the cell (related to the atom's size). Lookup, how the atoms are arranged in a HCP crystal structure and determine, what the unit cell looks like. Computing the volume of that object is plain mathematics and hardly has anything to do with chemistry.

 

 

Niobium has an atomic radius of 0.1430 nm and a density of 8.57 g/cm3. Determine whether it has an FCC or BCC crystal structure.

From the density you can compute how many atoms there are per cm3. Take the third root and you have the average number of atoms along 1 cm. Now imagine as if they are packed FCC or BCC. Does it fit or do you need overlapping spheres for the atoms. One structure does fit, the other doesn't.

[pacific]

thank u very much ....

u r really experiance in chemistry

[P-man]

I do not like this kind of questions. Do you want us to make your home work? I'll give you some hints, but please, next time, show that you've put some effort in the questions yourself.

You're right.