Answer : The concentration of needed is,
Explanation :
First we have to calculate the mole of phosphate.
As we are given that, 1 mg P/L that means, 1 mg of phosphate present in 1 L of solution.
Molar mass of phosphate = 94.97 g/mole
Now we have to calculate the concentration of phosphate.
Now we have to calculate the concentration of .
The second equilibrium reaction is,
The solubility constant expression for this reaction is:
Given:
Thus, the concentration of needed is,