To calculate the number of milligrams of Co^2+ in 1.0L of wastewater, let's go through the steps:
Step 1 - Determine the concentration of Co^2+ in the wastewater based on the absorbance value.
You mentioned that the absorbance was found to be 0.20. By referring to the calibration curve, you determined that 0.20 absorbance corresponds to a concentration of 0.05M.
Step 2 - Convert the concentration to moles.
To convert from moles to grams, you need to know the molar mass of Co^2+, which is 58.9 g/mol. Multiply the concentration (0.05M) by the volume (1.0L) to obtain the number of moles of Co^2+.
0.05 mol/L (0.05 mol/L) × (1.0 L) = 0.05 mol
Step 3 - Convert moles to grams.
Multiply the number of moles by the molar mass to obtain the mass of Co^2+ in grams.
0.05 mol × 58.9 g/mol = 2.95 g
Step 4 - Convert grams to milligrams.
To convert from grams to milligrams, multiply the mass by 1000.
2.95 g × 1000 mg/g = 2950 mg
Therefore, there are 2950 mg of Co^2+ in 1.0L of wastewater, and the correct answer is 2950 mg, not 0.0003 mg.