I have a water sample that contains 0.50 mg/l (or ppm) of phosphate.
We know that phosphate is a component of Total Phosphorous.
How do I calculate what the Total Phosphorous is from my sample that contains 0.50 mg/l of phosphate???
I have to do something with the atomic weights of P and O(4)...or divide P/O(4) or 30/64 but then what???
Many thanks.
a) Look up the atomic mass of P.
b) Calculate the formula mass of the phosphate ion, PO4^2-.
Multiply 0.50 mg/L by the fraction of (a)/(b).
[The above fraction is roughly 31/95, not 30/64]
So, Total Phosphorous is 0.16 mg/l?
That's correct.
I might point out here that 0.16 mg/L is the P in the phosphate which may or may not be the total P in the sample. IF all of the P in the sample was converted to phosphate, then phosphate determined, that represents the total P in the sample. However, if phosphate was determined without first making sure that ALL of the P was in the form of phosphate, then 0.16 may not represent total P. It's a picky point but worth pointing out, I think.
To calculate the Total Phosphorus in your water sample based on the phosphate concentration, you need to consider the atomic weights of phosphorus and oxygen. Here's how you can do it:
1. Determine the molecular weight of phosphate (PO4).
- Phosphorus (P) has a molecular weight of approximately 31.0 g/mol.
- Oxygen (O) has a molecular weight of approximately 16.0 g/mol.
- Since phosphate (PO4) contains one phosphorus atom and four oxygen atoms, the molecular weight of phosphate is:
Molecular weight of PO4 = (1 * 31.0 g/mol for P) + (4 * 16.0 g/mol for O) = 95.0 g/mol.
2. Calculate the concentration of Total Phosphorus (TP) from the measured phosphate concentration.
- Divide the concentration of phosphate (0.50 mg/L) by the molecular weight of phosphate (95.0 g/mol) to convert it to moles per liter (mol/L):
Concentration of TP = (0.50 mg/L) / (95.0 g/mol) = 0.0053 mol/L.
- However, please note that the units of the Total Phosphorus concentration will be in moles per liter (mol/L) and not in milligrams per liter (mg/L).
So, the Total Phosphorus concentration in your water sample, based on the given phosphate concentration of 0.50 mg/L, is approximately 0.0053 mol/L. Remember that this calculation assumes that all the phosphate present in the water sample is in the form of PO4.