What is the number of atoms on one unit cell of HCP?

ANALYSIS OF HCP UNIT CELL:

Number of effective atoms in HCP unit cell (Z):

Lattice point:  corner- total 12 carbon contribute 1/6 to the unit cell

Lattice point:   face- total face 2 contribute ½

Lattice point: body centre- total atom 3 (100% contribution)

Find the ratio of Fe+3 and Fe+2 in a non Stoichiometric oxide of iron , formulated as Fe_0.90 S_1.0 .

This is a non Stoichiometric compound formed due to variable valency of transition elements.   In the Compound Fe_0.90 S_1.0  both Fe+3 and F+2 ions present,  if number of  Fe+2 ions are  x then number of Fe+3 ions are (0.90-x).

We can find the value of x by oxidation state method as :

If the total number of atoms per unit cell in an hcp structure and a bcc structure gets halved, then ratio of percentage voids in hcp and bcc structures is

In HCP ; Packing efficiency:

Atoms occupy:74%

Empty space(voids): 28% 

In BCC; Packing efficiency:

Atoms occupy: 68% 

Empty space(voids): 32% 

According to the given condition if the total number of atoms per unit cell in a hcp structure and a bcc structure get halved. Then packing efficiency in HCP and BCC respectively given as:

In HCP ; Packing efficiency:

Atoms occupy: 74/2 = 37%

Empty space(voids): (100 - 37) = 63%

In BCC; Packing efficiency:

Atoms occupy: 68/2 = 34%

Empty space(voids): (100 - 34) = 66%

Then new ratio of their voids = 63%/66% = 21/22

What is relation between mole fraction and molality of solute ?

ILLUSTRATIVE EXAMPLES:

(1):Calculate the mole fraction of solute in the 12 molal aqueous solution of CaCO3.

(2):The mole fraction of glucose in aqueous solution is 0.2 , The molality of solution will be.

(3):If the mole fraction of a solute is changed from 1/4 to 1/2 in the 800 gm of solvent . then the ratio of molality will be .

(4):Mole fraction of I2 (iodine) in benzene (C6H6) is 0.2 . Calculate the molality of iodine (I2) in benzene.

(5):Calculate the amount of water that should be added to 16 gm methanol to make mole fraction of methanol as 0.25.?

Calculate the amount of water that should be added to 16 gm methanol to make mole fraction of methanol as 0.25.?