Can someone help me please!! I have no idea what i am doing. Please help explain

Question

Can someone help me please!! I have no idea what i am doing. Please help explain this to me! I have Part 1 done, i just really need help with Part 3

A scientist needed to determine the molarity of a solution of potassium permanganate. To do this, they used a 2.00e-4 M stock solution and a 100.00 mL volumetric flask to make diluted samples, and then analyzed them a spectrophotometer to find the absorbances. The sample of the unknown concentration was also analyzed, and was found to have an absorbance of 0.204.

Part 1. Diluting a stock solution

Molarity (M) Absorbance

Diluted sample | Vol (stock solution)(mL) | Unrounded value Rounded value   

1 2.8 5.60000x10^-5 5.6x10^-5 0.101

2 8.3 1.66000x10^-5 1.7x10^-5 0.299

3 13.9 2.78000x10^-5 2.78x10^-5 0.500

4 19.4 3.88000x10^-5 3.88x10^-5 0.698

5 25.0 5.00000x10^-5 5.00x10^-5 0.900

Part 2. Calibration Plot

Part 3. Determind the unknown Molarity

Unrounded value Rounded value  

Slope of graph (M^-1) ________________ ______________

y-intercept of graph _______________ ______________

Molarity of unknown solution (M) __________________ _________________

Take the cuvet path length to be 1 cm.

The last part is what i cannot get, please help today, THANK YOU SO MUCH!!

Beer's Law Calibration Plot 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0% y-18000x + 0 0 1x10 2x10- 3x10-5 4x105 5x10 6x105 Concentration, (M)

Explanation / Answer

Solution :-

The equation obtained for the straight line from the graph is

Y= mx+b

m = slope

Y=18000x+0

Slope of the line is 18000 M-1 cm-1

The slope is nothing but the coefficient of molar absorptivity

Therefore e = 18000 M-1 cm-1

Using this constant we can find the concentration of the unknown

Absorbance of the unknown = 0.204

Path length = 1 cm

Beers law formula

A= e*b*c

0.204 = 18000 M-1 cm-1 * 1 cm * c

0.204 / (18000 M-1 cm-1 * 1 cm) = c

1.13*10^-5 M = c

Therefore concentration of the unknown solution is 1.13*10^-5 M

Slope of graph (M^-1) = 18000

y-intercept of graph= 0

Molarity of unknown solution (M) = 1.13*10^-5 M

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