Nitrite ion, NO2-. is perservative for bacon and other foods, but it is potentia

Question

Nitrite ion, NO2-. is perservative for bacon and other foods, but it is potentially carcinogenic. A spectrophotometeric determination of NO2-, makes use of the following reactions:

Here is an abbreviated procedure for the determination:

1. To 50.0 mL of unkown solution containing nitrite is added 1.00 mL of sulfanilic acid solution.

2. After 10 min, 2.00 mL of 1-aminoaphtalene solution and 1.00 mL of buffer are added.

3. After 15 min, the absorbance is read at 520 nm in a 5.00-cm cell.

The following solutions were analyzed:

A. 50.0 mL of food extract known to contain no nitrite (that is, a negligible amount); final absorbance = 0.153.

B. 50.0 mL of food extract suspected of containing nitrite: final absorbance = 0.622.

C.Same as B, but with 10.0

Explanation / Answer

a. The absorbance due to the colored product from nitrite added to sample C is: A = 0.967 - 0.622 = 0.345 The concentration of colored product due to added nitrite in sample C is: Now applying Beer's Law: A = ?bc ? = A/bc ? = 0.345/ [(1.389x10-6M)(5.00cm)] = 4.97x104 M-1cm-1 b. 7.50x10-8 mol of nitrite (from 10.0?L added to sample C) gives A = 0.345. In sample B, x mole of nitrite in food extract gives: A = 0.622 - 0.153 = 0.469 Thus applying beer's law we have 2 samples: ? = A1bc1 ? = A2bc2 Since ? and b are the same in both, we can rearrange the equations and solve for ?/b = Ac. Now setting the two to equal each other gives: A1c1 = A2c2 c1/c2 = A2/A1 Notice here we just used moles as the volume remains constant. Thus solving for x gives x = 1.020x10-7 mol NO2- Converting to mass using the molecular weight: This isn't the answer you provided, 3.36, but I am confident that 4.69 is correct... Please let me know if something is still unclear. I hope this helped! :)

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