*kilograms to moles/ moles to kilograms*

Given: 1.0 kilograms of KClO3
Unknown: ? moles and ? milliliters

In this example the amount of moles (mol) in 360kg of hydrogen gas (H2) is calculated. Before beginning, the molar mass of H2 is needed. If you are wanting to convert the mass of a different element, you will need the molar mass of that element instead.

From Wolfram|Alpha; the molar mass of H2 is 2.01588 grams per mole.

Now, we need to convert kilograms (kg) to grams (g) as the molar mass is defined in grams.
Anything with the prefix "kilo" is 1000 times the rest of the unit name, in this case grams.
One kilogram is one thousand grams, so to convert kilograms to grams, multiply by 1000.

360 • 1000 = 360000g of hydrogen

To convert to moles, divide the mass by the molar mass for the element.

mass / molar mass = amount
360000 / 2.01588 = 179000 mol

Done. To convert grams to litres simply multiply the mass of the substance by its density. The density of most things is dependent on their temperature; for hydrogen gas at room temperature the density is 0.08375 grams per litre (g/L).

[mass x specific volume] or [mass/density] = volume
360000 • 0.08375 = 30150 L

You take the amount of moles you have of H2 and multiply it by 22.4 L over 1 mole of the given gas,this will give you the amount of liters.

.178 moles of H2 x 22.4 L = 3.992 Liters.
---------------------1 mol H2

--Then, to get from Liters to Milliliters, you multiply your liters by 1000.

3.992 x 1000 = 3,992 mL of H2

--As one large equation, this is what we just did:

360 Kg of H2 x 1 G x 1 Mol H2 x 22.4 L x 1000 mL = 3,992 mL of H2
-----------------1000 kgH2 2.02 g H2 1 Mol H2 1L

Now the other way

--If i have 256 mL of Oxygen (O2), how many Moles do you have? How Many Kilograms?

256 mL of O2 x 1 L = .256 L of 02
-------------1000 mL

--Then you multiply the amount of liters by 1 mole over 22.4 liters to get moles

.256 L O2 x 1 mole = .01138 Moles O2
-------------22.4 L

--This is the amount of moles of O2 you have, now moving onto kilgo grams. First, we must find out how many grams are in .01338 moles of O2. To do this, multiply the molar value by 1 mole of your gas (O2) divided by the molar mass of O2

.01138 x 1 Mol O2= .000355 grams of O2
------------32 g O2

--To finally turn this amount of grams into Kilograms, you must multiply the amount of grams by 1000

.000355 x 1000 = 3.55 Kg of O2

-the total equation is:

256 mL of O2 x 1 L x .256 L O2 x 1 mole x .01138 g x 1 Mol O2 x 1000 kg = 3.55 Kg of O2
-------------1000mL--------------22.4 L----------------32 g O2-----1 g