Artificial soil contamination
Hi guys, please, can anyone help me calculate the require amount in grams of 100 ppm As and 500 ppm Cr from Na2HAsO4.7H2O and K2Cr2O4 respectively to be added to 100 g soil in a pot experiment. Atomic weight (Na=23, H= 1, As= 75, O=16, K=39, Cr=52), Mass percent (Na= 25%, H= 1%, As= 40%, O= 34%) and (K= 31.76%, Cr= 42.24% O= 26%) respectively
This is a very basic, entry-level chemistry question.
First, calculate how much mass of As and Cr you need to add to the soil to get your desired concentration. 100 ppm is the same as 100 mg/Kg, so you need 10 mg of As and 50 mg of Cr.
So, if the sodium arsenate is 40% As, then to get 10 mg you would need to use 25 mg of the sodium arsenate. You calculate the chromium the same way.
One thing you didn't discuss but that you need to know is the background concentration of As and Cr in your soil. You'll need to adjust for this concentration if you want the final concentration to be 100 and 500 ppm, respectively
First of all, let me clarify the chemical formulas. If you are using a hydrated sodium arsenate (Na2HAsO4.7H2O), the molar mass of the substance is 300g/mol and the amount of As is 75g or 25% of total mass of the compound. For the second compound, is it potassium chrmoate, K2CrO4 or potassium dichromate, K2Cr2O7? These information must be clear enough so that your calculations can be more accurate.
ppm is 1 part per million or 1mg in 1,000,000mg; therefore 100ppm is 100mg in 1,000,000mg; for 100ppm in 100g, that would be 10mg or 0.01g of As in 100g of soil.. If this is the amount of As you need and you have a hydrated sodium arsenate, you will need 40mg of the compound or 0.04g of it.
in the case of the second compound, you will need 50mg or 0.05g of chromium; if you are using K2CrO4, you will need 186.54mg or 0.1865g of it; but if you are using K2Cr2O7, you must use 141.3mg or 0.1413g of it...I can give you the calculations if it can help..
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