How Do You Calculate Molar Mass from Concentration Data?

[3riefs]

Hello! I'm completing a lab for chemistry and would like some help on the last bit figuring out concentration then converting to molar mass. I need to make a data chart with a line of best fit on it with the dependent/independent variables. I understand that concentration is on the X-axis and the absorption is on the Y-axis. I used a spectrophotometer to track the different absorbency values of the different dilutions we made. I calibrated the machine using a "Blank" which was water in a test tube. I made a test solution, then made different dilutions using a stock solution provided to my class.

The observation chart that was produced looked like:

{Solutions}{Absorbency}{Wavelength (Blue)}​

Blank (H₂O) 0.00 470nm
Test Sol'n 5g solute/25mL H₂O 1.41 470nm
Stock Sol'n 0.83 470nm
0.40 mol/L sol'n 12mL S.S./3mL H₂O 0.70 470nm
0.30 mol/L sol'n 9mL S.S./6mL H₂O 0.58 470nm
0.20 mol/L sol'n 6mL S.S./9mL H₂O 0.40 470nm
0.10 mol/L sol'n 3mL S.S./12mL H₂O 0.21 470nm​

**Sol'n = solution**
**S.S. = stock solution**
**[ ] = concentration**

1. How do you find concentration?
2. How do you convert concentration to molar mass?

 

[Borek]

1. How do you find concentration?

Read it from the line of the best fit. Or, if you use linear regression, calculate concentration from absorbance. That's the same.

2. How do you convert concentration to molar mass?

Knowing concentration you will be able to calculate number of moles, knowing number of moles and mass of the sample you will be able to get molar mass.