How i will prepare a solution of known ppm of heavy metals to add it to the pot of 5 kg soil?
Dear Hina Jee,
First of all you have to analyze heavy metal content of your soil.
To prepare standard metal solution of known ppm select a salt of it. For eg. to prepare Cd standard of 1000 ppm just follow these steps:
- The most common form is the monohydrate CdSO₄·H₂O
- The molar mass is 208.47+18.01 = 226.48 g/mol.
- The atomic number of Cd is 48.
- Divide 226.48 by 48 i.e 4.7183.
- You have to weigh 4.7183 g of CdSO₄·H₂O and dissolve in 1000 mL DDW.
Thus, you can make standard solution of any metal and finally treat your soil.
Good luck.
Dear Pankaj,
Your example is very good, as well as the calculation, but there is a small error in the last step. The quantity of 4.7183 g CdSO4H2O should be dissolved in DDW in a 1 L volumetric flask, where DDW is added up to the mark. The DDW volume is not 1000 mL, this is the total volume of the aqueous solution which includes the hydrated cadmium sulphate. Cheers.
Dear Carmen Mateescu,
Thank you very much for telling me my error. I suggested cadmium mono-hydrate salt of CdSO₄·H₂O not tetra hydrated and I also added the molar mass of this single water molecule. I made an error in last step where total volume is to be made 1 L with DDW.
ppm means parts per million equivalent to mg/L. Weigh (with analytical balance) a known amount of metallic salt (analytical grade) containing the specific amount of metal that will give you the ppm you require and dissolve in specific amount of deionised water (you may need to dissolve in a little quantity of acid first if salt is not water soluble) to get desired concentration. Alternatively you can dissolve the pure metal and dilute accordingly. For instance 1.2450g of ZnO contains 1 g of Zn & when dissolved in 1L of water gives 1000ppm while 0.0012g in 1L of water gives 1ppm. 1 g (or 0.001g) of Zn metal dissolved in 1L of water also give 1000 (or 1) ppm solution
Pankaj... In water solution the ppm refers to mg per liter. For soil ppm means mg per Kg of soil or ug per gram of soil. So to get the right ppm in soil, we prepare a stock solution of the specific metals (Either by dissolving exactly one gram of pure metal and dissolve it in few mLs of a mineral acid, preferably nitric, and complete the volume to one liter with water. To transport the metal content into the soil you need to consider the following:. Each mL of the solution contains 1.0 mg of the metal. To get 100 g of soil with a Zn content of 50 ppm, i.e. we need 100 g x 50 ug of Zn= 5000 ug = 5.0 mg. Now we must pipet the volume of Zn Stock solution which contains the 5.0 mg and mix it it with 100 g of soil. This is a 5 mL aliquot. Now put your 100 g of soil in a beaker or flask and add to it 5.0 mL of the 1000 ppm solution. Add more water to facilitate mixing. Thorough mixing is necessary to guarantee the even distribution of the metal in soil. After mixing the beaker content is allowed to dry naturally to end up wit a soil sample contaminated with Zn at a level of 50 ug per g of soil. Good luck
Pankaj,
If you look carefully at the reply given by Carmeen(Carmen Mateescu), it is monohydrate (CdSO4.H2O) and not tetrahydrate (CdSO4.4H2O). Perhaps its a formatting miss where a dot (.) got you confused.
Your explanation for ppm conversion is good.
Dear Anju Baroth I apologize for the same.
Thank you Carmen Mateescu again.
Dear Mahmood M. Barbooti,
Known concentration of heavy metal treatment in soil samples can be achieved by mixing the stock solution and standardized accordingly.
Thus, this will become an optimization study.
Agree with Pankaj.... The explanation is very good and make clear all the doubts about this question.
Thank you Pankaj
Dear Hina Jee
You got very good and will explained reply. Also note one example here for copper, prepared from hydrated copper sulfate.
Heavy metals are many. Parts per million (ppm ) is very much quantitative issue.Thus making solution may differ from one heavy metal to another.
Kind regards Pankaj Kumar , where does the mathematical value of 18.01 of the second item molar mass come from, please clarify that question for me
Dear Cristhian John Macías Holguín , The mathematical value (18.01528 g/mol) is nothing but molar mass of water molecule (H2O). We must add it in the calculation since we are taking CdSO₄·H₂O which contains one water molecule also. Thank you
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