Question

Exercise 2: Beer’s Law Curve and Unknowns

Data Table 1. Concentration and Resistance.

Tube Label	Concentration of Blue Dye in Test Tube (M)	Resistance Reading on Colorimeter (Ω)
B	2.57 x 10-4 M	3.6
1		3.4
2		3.3
3		3.1
4		3.0
5		2.9
6		2.8
7		2.7
8		2.6
9		2.4
W	0 M	2.2
CD 1		2.7
CD 2		2.4

How do I fill the blanks in? I understand that I am suppose to use M1V1 but I am COMPLETELY lost.

Answer 1

M1V1 = M2V1 is used to find the concentration of final solution.

For tube B, volume of standard blue dye = 5 mL

Total volume in test tube = 5.0 mL

Concentration of blue dye = 2.57 x 10^-4 M

In tube level 1 –

Concentration of blue dye in tube 1 = Volume of stock solution with molarity 2.57 x 10^-4M is 5.0 mL

From this stock solution we use 0.5 mL of this stock solution and dilute to 5.0 mL in tube1.

M1= 2.57 x 10^-4 M, V1 = 4.5 mL, V2 = 5.0 mL and we have to calculate M2

M2 = M1V1/V2 = 2.57 x 10^-4 M x 4.5ml/5ml = 2.31 x 10^-4 M

In tube level 2 -

We have 4.0 mL of stock solution and so its M1= 2.57 x 10^-4M, V1 = 4.0 mL , V2 = 5.0 mL

M2 = 4.0 mL x 2.57 x 10^-4M / 5.0 mL

= 2.06 x 10^-4M

In tube level 3-

M2 = 3.5 mL x 2.57 x 10^-4M / 5.0 mL

M2= 1.80 x 10^-4M

In tube level 4-

M2 = 3.0 mL x 2.57 x 10^-4M / 5.0 mL

M2 = 1.54 x 10^-4M

In tube level 5

M2 = 2.5 mL x 2.57 x 10^-4M   / 5.0 mL

M2 = 1.23 x 10^-4M

In tube Level 6

M2 = 2.0 mL x 2.57 x 10^-4M / 5.0 mL

M2 = 1.03 x 10^-4M

In tube level 7

M2 = 1.5 mL x 2.57 x 10^-4M / 5.0 mL

M2 = 7.71 x 10^-5M

In tube level 8

M2 = 1.0 mL x 2.57 x 10^-4M / 5.0 mL

M2 = 5.12 x 10^-5M

In tube level 9

M2 = 0.5 mL x 2.57 x 10^-4M / 5.0 mL

M2 = 2.57 10^-5 M

In tube level 10 there is no presence of dye, so Molarity of dye would be zero.

Data-Table 1 Concentration and Resistance

Tube Label         Concentration of Blue Dye in Test Tube (M)        Resistance Reading on Colorimeter (Ω)

B 2.57 x 10-4 M                                                              3.6

1                                         2.31 x 10^-4 M                                                            3.4

2                                         2.06 x 10^-4M                                                           3.3

3                                         1.80 x 10^-4M                                                             3.1

4                                         1.54 x 10^-4M                                                            3.0

5                                         1.23 x 10^-4M                                                            2.9

6                                         1.03 x 10^-4M                                                             2.8

7                                         7.71 x 10^-5M                                                            2.7

8                                         5.12 x 10^-5M                                                            2.6

9                                         2.57 x 10^-5 M                                                                        2.4

10                                                     0                                                                      2.2

CD1                                    7.71 x 10^-5 M                                                           2.7

CD2                                    2.57 x 10^-5 M                                                           2.4