Question 1 from 100 mg of K 2 Cr 2 O 7 dissolved in 1 L of Deionized water is di

Question

Question 1

from 100 mg of K2Cr2O7 dissolved in 1 L of Deionized water is diluted up to 1 mL using the micropipette and a volumetric flask. The formula mass and molar absorptivity of K2Cr2O7 is 294.2 and 4766 respectively. If the absorbance reading of the diluted solution reads 0.320 in a spectrophotometer with a 10mm light path, then calculate the percent error of the micropipette. Show all calculations.

Question 2

A spectrophotometric check is performed on a 200uL micropipette: 200uL of a solution ?

Question 3

In a total protein analysis where the color follows Beer’s Law, a patient’s serum had an absorbance of 0.300 at 540nm; a 5.0 g/L standard had an absorbance of 0.250 at 540 nm, the patient’s protein concentration is:

Question 4

  A sodium concentration is reported as 326 mg/dL. The concentration expressed in mEq/L is: (atomic weight Na is 23):

Explanation / Answer

1. Percent error = (accepted value – experimental value / (accepted value) * 100%

expt value=0.32. accepted value = A = -log(I/Io), which is - log(molar absorptivity)

% error = 0.32/ -log (4766) *100

2. % error will not effect since 200ul is pipetted in 200ul pipette

3. A = ebsilon* b*C. where  absorbance (A), the molar absorptivity (ebsilon), the distance the light travels through the sample (b), and the concentration of the substance absorbing the light (C)

C= A/ ebsilon *b = 0.3/ ebsilon * 5g/l

4. mEq/L= molecular weight of Na2= 46. therefore 326/46

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