[Grizelda]

To whom it may concern,

I am a trainee chemist for a company in South Africa, and are working on a small project. i have a situation where I make for example a 30% KNO2 solution, and of this solution I add 2 ml directly to a 5ml water sample which was then made up to 50ml in a volumetric flask.

I want to calculate the dosage rate of pure KNO2 which is neccesary to reduce the 5 ml sample. I made a simple caculation: C1V1=C2V2, (0.3g/ml)(2ml) = c2(50 ml), c2 = 0.012 g/ml.

Does this then mean that the dosage rate to reduce my 5 ml sample is 0.012g/ml (12 g/L), or do I need to take into account the dilution of the sample?

Any help would be much appreciated  .

Kind regards...

[Borek]

i have a situation where I make for example a 30% KNO2 solution, and of this solution I add 2 ml directly to a 5ml water sample which was then made up to 50ml in a volumetric flask.

This is convoluted. Why not put 2 mL directly to the volumetric flask and dilute to 50 mL? Why do you need 5mL as an intermediate step?

I want to calculate the dosage rate of pure KNO2 which is neccesary to reduce the 5 ml sample.

Do you mean the 5mL sample contained something that you are reducing? If so, it is about stoichiometry and you need to know how much of the other substance was present.

I made a simple caculation: C1V1=C2V2, (0.3g/ml)(2ml) = c2(50 ml), c2 = 0.012 g/ml.

I guess 0.3g/mL means you are assuming the density of 30% KNO₂ solution is that of water - 1g/mL? This is a concentrated solution, so you are way off. You need to use density tables (KNO₂ density table is built into my concentration calculator).

[Grizelda]

Okay, let me give you more detail. I want to reduce Cr6+ to Cr+3 in a water sample. According to our standard procedure, I am obligated to use 5 ml of this water sample and then make up to 50 ml in a volumetric flask.

Now, I am exploring the reduction capabilities of NaNO2 (which I already know to work successfully) I made a 30% NaNO2 solution (30g/100ml) of which I added for example 2 ml of this solution to the Cr+6 sample to reduce from 10 ppm to less than 2 ppm.

Now I need to calculate the actual dosage rate of NaNO2 to water to reduce Cr6+ in order to use on a industrial scale for water dams.

[Borek]

Now I need to calculate the actual dosage rate of NaNO2 to water to reduce Cr6+ in order to use on a industrial scale for water dams.

So, as I wrote earlier - it is about stoichiometry. You need to know Cr(VI) concentration and start from there.