Question

A solution is prepared by mixing 50ml from 0.5M orthophosphate(PO4^-3) 35ml from 500ppm(mg/L) PO4^-3 solutions then complete to 250 ml total volume.What is the final concentration of Phosphate anion(PO4^-3) in both ppm and polarity.Give the concentration in ppm to 4 significant figures and in polarity to 7 significant figures.

Answer 1

To find the final concentration of phosphate anion (PO4^-3) in both ppm and molarity, we can follow these steps.

1. Calculate the amount of PO4^-3 from each component before mixing:

   • From the 0.5M orthophosphate solution:

     • Volume = 50 mL = 0.050 L
     • Concentration = 0.5 M
     • Moles of PO4^-3 = Concentration × Volume = 0.5 mol/L × 0.050 L = 0.025 moles

   • From the 500 ppm PO4^-3 solution:

     • 500 ppm = 500 mg/L
     • Volume = 35 mL = 0.035 L
     • Concentration in mg/L can be converted to moles:
       • Molar mass of PO4^-3 (Phosphate) is approximately 94.97 g/mol, or 94,970 mg/mol.
       • Moles of PO4^-3 = (500 mg/L × 0.035 L) / 94,970 mg/mol
       • Moles of PO4^-3 from 35 mL = (17.5 mg) / (94,970 mg/mol) = 0.000184 moles (approximately).

2. Total moles of PO4^-3:

   • Total moles = Moles from 0.5M solution + Moles from 500 ppm solution
   • Total moles = 0.025 moles + 0.000184 moles = 0.025184 moles (approximately).

3. Find the final volume of the solution:

   • The final total volume of the solution is 250 mL = 0.250 L.

4. Calculate the final molarity (polarity): $$\text{Molarity (M)}=\frac{\text{Total moles}}{\text{Total volume in liters}}=\frac{0.025184\text{ moles}}{0.250\text{ L}}=0.100736\text{ M}$$

   (To 7 significant figures: 0.1007360 M)

5. Calculate the final concentration in ppm:

   • We need to convert the total moles of PO4^-3 back to mg. $$\text{mass of PO4}=\text{Total moles}\times \text{Molar mass}=0.025184\text{ moles}\times 94.97\text{ g/mol}=2.393\text{ g}=2393\text{ mg}$$

   Now, to find the concentration in ppm: $$\text{ppm}=\frac{\text{mass of solute (mg)}}{\text{volume of solution (L)}}=\frac{2393\text{ mg}}{0.250\text{ L}}=9572\text{ ppm}$$

   (To 4 significant figures: 9572 ppm)

Final Results:

• Concentration in ppm: 9572 ppm
• Concentration in molarity: 0.1007360 M