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Figuring out Concentration?

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3riefs
#1
Apr18-11, 05:40 PM
P: 1
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?
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Borek
#2
Apr20-11, 02:51 AM
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P: 23,599
Quote Quote by 3riefs View Post
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.


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