Question

In: Chemistry

You wish to measure the iron content of the well water on the new property you...

You wish to measure the iron content of the well water on the new property you are about to buy. You prepare a reference standard Fe3 solution with a concentration of 6.52 × 10-4 M. You treat 13.0 mL of this reference with HNO3 and excess KSCN to form a red complex, and dilute the reference to 60.0 mL. The diluted reference is placed in a cell with a 1.00-cm light path. You then take 30.0 mL of the well water, treat with HNO3 and excess KSCN, and dilute to 100.0 mL. This diluted sample is placed in a variable pathlength cell. The absorbance of the reference and the sample solutions match when the pathlength is 3.99 cm. What is the concentration of iron in the well water? For each solution, the zero is set with a blank. Please give in correct sig figs!!

Solutions

Expert Solution

Ans. Step 1: Standard Fe3+ solution: 13.0 mL of 6.52 x 10-4 M is diluted to a final volume of 60.0 mL.

Now, using    C1V1 (standard Fe3+ solution) = C2V2 (diluted Fe3+ solution)

            Or, 6.52 x 10-4 M x 13.0 mL = C2 x 60.0 mL

            Or, C2 = (6.52 x 10-4 M x 13.0 mL) / 60.0 mL = 1.4127 x 10-4 M

Thus, [Fe3+] in final diluted aliquot (whose Abs is taken) = 1.4127 x 10-4 M

Step 2: Beer-Lambert’s Law, A = e C L             - equation 1,              

where,

                                                A = Absorbance

                                                e = molar extinction coefficient (M-1cm-1)

                                                L = path length (in cm)

                                                C = Molar concentration

Putting the values for standard Fe3+ solution in equation 1-

            A = e x 1.4127 x 10-4 M x 1.0 cm                        - equation 2

# Step 3: Water sample from Well

Let [Fe3+] in original water sample be X.

30.0 mL of original well water sample is diluted to a final volume of 100.0 mL

Again, using C1V1 (original well water) = C2V2 (diluted well water)

            Or, C2 = (X x 30.0 mL) / 100.0 mL = 0.30X

Hence, [Fe3+] in final diluted water sample (whose Abs is taken) = 0.30X

Putting the values in equation 1 for diluted water sample-

            A = e x 0.30X x 3.99 cm                            - equation 3

Step 4: Given,

Both the diluted water sample and diluted standard Fe3+ solutions give same absorbance at different path length.

Note that molar extinction coefficient e remains constant.

Now,

            Comparing equation 2 and 3-

            e x 1.4127 x 10-4 M x 1.0 cm = e x 0.30X x 3.99 cm

            Or, 0.30X = (e x 1.4127 x 10-4 M x 1.0 cm) / (e x 3.99 cm)

            Or, 0.30X = 3.5406 x 10-5 M

            Or, X = (3.5406 x 10-5 M) / 0.30

            Hence, X = 1.180 x 10-4 M

Therefore,, [Fe] in original well water sample = X = 1.18 x 10-4 M


Related Solutions

You wish to measure the iron content of the well water on the new property you...
You wish to measure the iron content of the well water on the new property you are about to buy. You prepare a reference standard Fe3 solution with a concentration of 7.66 × 10-4 M. You treat 11.0 mL of this reference with HNO3 and excess KSCN to form a red complex, and dilute the reference to 60.0 mL. The diluted reference is placed in a cell with a 1.00-cm light path. You then take 35.0 mL of the well...
Iron-59 has a half-life of 45.1 days. How old is an iron nail if the Fe-59 content is 25% that of a new sample of iron?
Iron-59 has a half-life of 45.1 days. How old is an iron nail if the Fe-59 content is 25% that of a new sample of iron?   Show all calculations leading to a solution.
Suppose you have the opportunity to define a new system of property rights for water. What...
Suppose you have the opportunity to define a new system of property rights for water. What are the most important attributes you would want to ensure for your property rights and why?
The mass of a sample or iron ore is known to be 35.714 grams. You measure...
The mass of a sample or iron ore is known to be 35.714 grams. You measure the mass of this sample using three different scales and obtain the following masses: 36.2 g, 35 g, 34.9 g and 35.9 g. The accepted tolerance for both error and for accuracy is 2%. With respect to accuracy and precision, how would you best describe these measurements? Hint: Determine the average mass, absolute deviation for each trail, the M.A.D, and Relative Deviation (percent).
GDP is often used as a measure of well-being. Is it a reasonable measure of well-being?...
GDP is often used as a measure of well-being. Is it a reasonable measure of well-being? If so, why does Norway with its high standard of living have a relatively low GDP? Why do India and China, with their relatively low standards of living have some of the highest GDP in the world?
You are a digital content developer and you own your own digital publishing establishment. You wish...
You are a digital content developer and you own your own digital publishing establishment. You wish to expand your readers’ target audience reach base with another digital publishing establishment who has the audience you desire to reach and capture. The other digital publishing establishment envy’s your online advertising reach for advertisers and the creative expertise you have for graphic designing. And you like to share the use of the other digital publisher’s servers as he/she has data storage capacity of...
Assume the following half reactions: You have water-soluble iron(II)- and iron(III)- chloride salts, KCl, water, two...
Assume the following half reactions: You have water-soluble iron(II)- and iron(III)- chloride salts, KCl, water, two beakers, a U-shaped tube, two platinum wires, two copper clips that can connect to and hold the platinum wires, agar (a gel), a silver wire coated with AgCl and voltmeter. (3) how you can make a voltage source out of (a subset or all of this. What is the standard potential difference you can get (3)? You can vary the actual voltage by changing...
Assume you wish to purchase a property for $400,000 and you are evaluating two mortgage choices....
Assume you wish to purchase a property for $400,000 and you are evaluating two mortgage choices. You are only able to afford a 10% downpayment, so you have the following options. The first option is a 4.75% fully amortizing, monthly payment, fixed rate loan for 30 years with $2000 in origination fees and no points. This loan is for 90% of the purchase price. Alternatively, you can borrow 80% of the purchase price at a rate of 3.875%, with $4000...
Write down 7 facts or statements about the following; To measure the iron in vegetables, iron...
Write down 7 facts or statements about the following; To measure the iron in vegetables, iron must be extracted and complexed with 1,10-phenanthroline to create iron(II)tris(phenanthroline). An aliquot of a 50 mL sample measured in the lab was found to have an absorbance of 1.02 when measured in a cell with a path length of 1.00 cm. The molar absorptivity of iron(II)tris(phenanthroline) at 508 nm is 1.11 x 104 M-1cm-1.
Problem 2. You wish to determine the energy content per gram and Calories per serving of...
Problem 2. You wish to determine the energy content per gram and Calories per serving of a chocolate chip cookie and a banana bread slice from the Student Union to decide which is less “fattening.” The intact cookie and banana bread slice you are analyzing weigh 72.501 g and 69.003 g, respectively. Before you can analyze the samples, the calorimeter heat capacity must be determined. It is known that combustion of 1.000 g of benzoic acid releases 26.44 kJ of...
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT