Question 1 If a Fe stock solution has a concentration of 2 mg/mL, what is the co

Question

Question 1

If a Fe stock solution has a concentration of 2 mg/mL, what is the concentration when 2 mL of this stock solution is diluted to 50. mL? Keep 2 sig figs for the answer.

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Question 2

What is the absorbance if the % transmittance is 43%? Keep 2 sig figs for the answer.

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Question 3

The Total Cereal has a Fe concentration of 0.6 g Fe per g of Cereal. However, it is very common for students to get less than 0.6. Which of the following can be contributors to this lower experimental result than the manufacturer listed value? There are three correct answers and find all of them.

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Question 4

A=ebc, where A is absorbance, which is unit-less, b is path length that is 1 cm for the cuvette used. If the concentration c uses mol/L, what unit should the extinction coefficient e have?

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Question 5

Keep in mind that the absorbance was plotted on the y-axis and concentration of Fe in mg/mL was plotted on x-axis to get best-fit line equation from the standard solutions. If the best fit line equation is

y = 100x +0.01

What is the Fe concentration in mg/mL if the absorbance is 0.21 based on the best-fit line equation? Keep two sig figs for your answer.

Explanation / Answer

1. concentration of Fe stock solution = 2 mg/ml

when 2 ml of this solution is diluted to 50 ml

concentration of diluted solution = 2 x 2/50 = 0.08 mg/ml

2. Absorbance = 2 - log(%T)

= 2 - log(43) = 0.366

3. the measured low Fe content in cereals could be due to,

loss of Fe during few transfers between glasswares

4. the units of extinction coefficient would be,

L/(mol.cm)

5. Fe concentration

A = ebc

y = 100x + 0.01

A = 0.21

0.21 = 100x + 0.01

concentration of Fe = x = 0.002 mol/L = 0.002 x 55.845 x 1000/1000 = 0.112 mg/ml

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