[Amrik]

I am stuck a bit with this question
The body centered cubic cell of iron has a length of 0.286 nm. Calculate the density of iron (g/cm^3).

how should i do it? i did it this way
mass = 55.8g/mol  * 1 mol/6.022x10^-23 = 9.266x10^-23g x 2ions/ 1 ion = 1.853x10^-23 g

volume = (0.286 x 10^-7cm)^3 = 2.339 x 10^-23 cm^3

denisty = 1.853 x 10^-23 g / 2.399 x 10^ - 23 cm^3 = 7.922 g/cm^3

is it correct? well i got  0.5/1 (or) 2 i just cannot remember

[Dan]

I am stuck a bit with this question
The body centered cubic cell of iron has a length of 0.286 nm. Calculate the density of iron (g/cm^3).

how should i do it? i did it this way
mass = 55.8g/mol  * 1 mol/6.022x10^-23 = 9.266x10^-23g x 2ions/ 1 ion = 1.853x10^-23 g

volume = (0.286 x 10^-7cm)^3 = 2.339 x 10^-23 cm^3

denisty = 1.853 x 10^-23 g / 2.399 x 10^ - 23 cm^3 = 7.922 g/cm^3

is it correct? well i got  0.5/1 (or) 2 i just cannot remember

I think you are out by a power of 10 in right hand side the highlighted bits. However, you are out by a factor of ten one way in one calculation, and the other way in the other, so your errors have cancelled.
Apart from that, I think it is right.

[Amrik]

Out by a power of 10...can you explain that a bit more Dan  I did it the exact same way how they did it in here Chemistry
in the website you scroll down a bit and their will be ">> Explore: Unit Cell Tutorial " that is where i got it from

2 more questions please

Q1. An arrangement in which every other layer is identical (ABABABAB) is :
a) Octahedral Holes
b) Tetrahedral holes
c) hexagonal close packing
d) cubic close packing

Ans - is it (c) hexagonal close packing?

2. A crystal that does not conduct electricity, even after melting. It is hard and brittle, it melts at a very high temperature. What type of a crystal is it?

Ans - it is a covalent network crystal right?

[english]

I am stuck a bit with this question
The body centered cubic cell of iron has a length of 0.286 nm. Calculate the density of iron (g/cm^3).

how should i do it? i did it this way
mass = 55.8g/mol  * 1 mol/6.022x10^-23 = 9.266x10^-23g x 2ions/ 1 ion = 1.853x10^-23 g

1 mol of iron is 6.022 x 10²³ ions. 

Also, 0.286 nm = 2.86 x 10^-12cm

[Borek]

1 mol of iron is 6.022 x 10²³ ions.

More likely atoms in this case.

Also, 0.286 nm = 2.86 x 10^-12cm

huh?

1 nm = 10^-9m

1 cm = 10^-2m

[english]

1 mol of iron is 6.022 x 10²³ ions.

More likely atoms in this case.

Also, 0.286 nm = 2.86 x 10^-12cm

huh?

1 nm = 10^-9m

1 cm = 10^-2m

I meant 1 x 10^-8 cm

He was right originally I didn't see that 

[Dan]

I am stuck a bit with this question
The body centered cubic cell of iron has a length of 0.286 nm. Calculate the density of iron (g/cm^3).

how should i do it? i did it this way
mass = 55.8g/mol  * 1 mol/6.022x10^-23 = 9.266x10^-23g x 2ions/ 1 ion = 1.853x10^-23 g

Should be

mass of iron atom = 55.8 / 6.022x10⁺²³ = 9.266x10^-23g
mass of two iron atoms = 1.853x10^-22

volume = (0.286 x 10^-7cm)^3 = 2.339 x 10^-23 cm^3

correct

denisty = 1.853 x 10^-23 g / 2.399 x 10^ - 23 cm^3 = 7.922 g/cm^3

denisty = 1.853 x 10^-22 / 2.399 x 10^-23 = 7.922 g/cm^3

so your answer is correct, but your working is not quite right

[Borek]

Also, 0.286 nm = 2.86 x 10^-12cm

huh?

1 nm = 10^-9m

1 cm = 10^-2m

I meant 1 x 10^-8 cm

Even with -8 you will be still wrong 

[Dan]

Even with -8 you will be still wrong 

No, he'd be right, 0.286 x10 ^-7 = 2.86 x10 ^-8

[Amrik]

I am stuck a bit with this question
The body centered cubic cell of iron has a length of 0.286 nm. Calculate the density of iron (g/cm^3).

how should i do it? i did it this way
mass = 55.8g/mol  * 1 mol/6.022x10^-23 = 9.266x10^-23g x 2ions/ 1 ion = 1.853x10^-23 g

Should be

mass of iron atom = 55.8 / 6.022x10⁺²³ = 9.266x10^-23g
mass of two iron atoms = 1.853x10^-22

volume = (0.286 x 10^-7cm)^3 = 2.339 x 10^-23 cm^3

correct

denisty = 1.853 x 10^-23 g / 2.399 x 10^ - 23 cm^3 = 7.922 g/cm^3

denisty = 1.853 x 10^-22 / 2.399 x 10^-23 = 7.922 g/cm^3

so your answer is correct, but your working is not quite right

ok i know now that i was wrong about this "mass of two iron atoms = 1.853x10^-22"

but this one

mass of iron atom = 55.8 / 6.022x10⁺²³ = 9.266x10^-23g

if i divide it using +23 how can i get an answer with the power -23?...I tried doing it with my calculator i get a power of +23 not -23

[Dan]

you must be inputting it wrong. Put brackets around 6.022 x10 ²³

Note that dividing by 10²³ is the same as multiplying by 10^-23

[Amrik]

  yeah...i did really input it the wrong way!
Thanks alot for the help Dan!.