Answer:
We need to add [tex]5 \times 10^{-4}[/tex] mg
Explanation:
Remember first:
[tex]ppm(w/w) = \frac{g_{solute}}{g_{solution}}\times 10^{-6}\\ppm(w/v)= \frac{1 g_{solute}}{1000mL_{solution}}\\g_s= grams\ of\ sample\\mL_s= mL\ of\ sample[/tex]
To calculate this mass, we need to calculate the concentration as follows:
[tex]\frac{x\ mg_s}{100mL_s} \times \frac{1g_s}{1000 mg_s} \times \frac{200gCa}{g_s} \times 10^6= 2000x \frac{gCa}{mL_s}[/tex]
Here we have the concentration of the sample in terms of x, being x the mg needed to have a solution of 1ppm (w/v). Therefore, we solve the system as follows:
[tex]2000x \frac{gCa}{mL_s}=\frac{1gCa}{1000mL_s}\\x= \frac{1mL_s}{2000\times 1000}= 5\times 10^{-7} g= 5\times 10^{-4} mg[/tex]
Finally we need [tex]5\times 10^{-4}[/tex] mg of sample to have a Ca concentration of 1ppm (w/v) in the final solution.
