[listan]

I need to calculate how much NaHSO3 is needed to consume the oxygen in a pure water solution containing 1 ppm of oxygen. Using the asumption that 1 NaHSO3 molecule consumes 1 oxygen molecule.

Anyone know this?

[Arkcon]

You can start with a balanced equation, but you don't need one, with your given info.  You have the amount of oxygen in ppm, you have to do a unit conversion, to use your given relation.  What units you'll use at the end, will depend on what units the question asks for, and may require another units conversion.  This does all depend on your definition of ppm, which is not as well defined as most people would hope it was.

[listan]

The answer should have units mg/dm3...

[AWK]

The assumption is chemically completely wrong.
1 NaHSO3 consumes 1 atom of oxygen not 1 molecule

[listan]

ok, my bad.. i dont know the exact reaction.
i guess this mean that you need 2 NaHSO3 molecules to consume 1 O2 molecule.

My main problem is to convert from 1 ppm O2 dissolved in water to amount in mg/dm3.

[AWK]

Use defonition of ppm, convert it to grams, then moles, do stoiciometry and finally convert moles of NaHSO4 to miligrams.

[listan]

The problem is that i have not found the definition on how to convert 1 ppm O2 to mg/dm3.

[Borek]

The problem is that i have not found the definition on how to convert 1 ppm O2 to mg/dm3.

Assuming it happens in diluted water solution - what is mass of dm³ of solution?

[JGK]

The problem is that i have not found the definition on how to convert 1 ppm O2 to mg/dm3.

http://www.lenntech.com/calculators/converter-parts-per-million.htm

will get you to mg/m3 you could do the conversion from there.