Hello, Rasmus,

I am having trouble interpreting a few of your questions, so I've rewritten a couple the way I think you meant them (revisions are in **BOLD**.)

__How many ____per____ gram____s in____ 3.01 x 10__^{22}__ molecules of nitric acid?__

A mole of Nitric acid contains 6.02x10^{23} molecules, and has a mass equal to it's molar mass, 63.0 g/mole. We can use this as a conversion factor:

(63.0 g HNO_{3}/6.02x10^{23} ~~molecules HNO~~_{3}) x (3.01 x 10^{22} ~~molecules HNO~~_{3}) = 3.16 g HNO_{3}

__What is the volume of ____2.408____ x 10__^{24}__ molecules of oxygen?__

(** 2.408** x 10

^{24}molecules)/(6.02x10

^{23}molecules/mole) = 4.01 moles O

_{2}. Since we are not told the pressure or temperature, we'll assume it is STP, and then we know that one mole of any gas occupies 22.4 liters.

(4.01 moles O_{2})x(22.4 liters/mole O_{2}) = 9.7 liters

__How Many Molecules are in 112 dm__^{3}__ of Hydrochloride?__

__Should we assume this is a gas? My answer depends on it, otherwise we would need a density.__

1 dm = 10 cm

1 dm^{3} = 1000 cm^{3}

1 cm^{3 }= 1 ml

112 dm^{3} = 112 ml, or 0.112 liters

(0.112 ~~liters~~)x(1 mole/22.4 ~~liters~~) = 0.005 moles

0.005 ~~moles~~ x(6.01x10^{23 }molecules/~~mole~~) = 3.01x10^{21} molecules HCl

__How many grams ____in____ 134.4 dm3 of sulfur trioxide__

Convert cubic dm into liters, as in the above example. Use 1 mole/22.4L to obtain the moles of SO_{3} . Once you have moles, multiply that by the molar mass SO_{3} (g/mole).

I hope this helps,

Bob