In order to analyze the waste water containing Co^2+ from a manufacturing process, 1.0L of water was evaporated to 10.0mL, then placed in a spectrophotometer tube. The absorbance was found to be 0.20. Using your calibration curve, calculate the number of milligrams of co^2+ in 1.0L of waste water.

Step one - Using calibration graph: 0.20 absorbance = 0.05M

Step two - 0.05M x 1.0L = 0.05mol

Step three - 0.05mol x 58.9g/mol = 2.945 = 3g

Step 4 - 3g = 0.0003mg

There are 0.0003mg Co^2+ in 1.0L of water.

Can someone check if this is the answer to the question? I'm not sure if this is how I'm supposed to do. If I'm wrong, please correct me.

Thank you very much.

The absorbacne of 0.20 corresconds top the concentrated sample.

Step one - Using calibration graph: 0.20 absorbance = 0.05M
-OK

so the concentration in the original solution is

0.05 M/100=0.0005 M (the sample was concentrated by a factor of 100)

Step three - 0.0005 mol x 58.9g/mol = 2.945 = 0.0285 g

so there is 29 mg of CO2+ per litre of water.

mg = (1000mg/1g) × (58.9g/1mol) × (0.05mol/1L) × 0.010L = 28mg

Well, I must say, you're pretty close with your calculations! However, I think you made a small error in Step three. Let me help you fix it.

Step one - Using calibration graph: 0.20 absorbance = 0.05M

Step two - 0.05M x 1.0L = 0.05mol

Step three - 0.05mol x 58.9g/mol = 2.945g (or 2.95g to be more precise)

Step 4 - 2.95g = 0.00295g

So, there are 0.00295g (or 2.95mg to be more precise) of Co^2+ in 1.0L of wastewater.

Great job on getting most of the steps right! Keep up the good work!

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.

Your approach is almost correct, but there is a small mistake in Step 4.

Step 1: You determined that an absorbance of 0.20 corresponds to a concentration of 0.05 M based on the calibration curve.

Step 2: You multiplied the concentration (0.05 M) by the volume (1.0 L) to get the number of moles: 0.05 M x 1.0 L = 0.05 mol.

Step 3: To calculate the mass, you multiplied the number of moles (0.05 mol) by the molar mass of Co^2+ (58.9 g/mol), which gives you 0.05 mol x 58.9 g/mol = 2.945 g.

Step 4: However, there was a mistake in converting grams to milligrams. 2.945 grams is equal to 2945 milligrams (not 0.0003 mg). So, the correct answer should be 2945 mg.

Therefore, the correct answer is that there are 2945 milligrams of Co^2+ in 1.0 liter of wastewater.