I am doing a lab and I am given the question \"Use the Molarity of the solution

Question

I am doing a lab and I am given the question "Use the Molarity of the solution to calculate the number of milligrams of Fe in the vitamin tablet. Remember to use appropriate dilution factors in your calculation." How would I calculate this? My data is:

The tablet was boiled until dissolving in 25 mL of 6 M HCl, then it was filtered and 5 mL of the filtered solution was put into a 100 mL volumetric flask and diluted to 100 mL. Then, 5 mL of the more diluted solution was put into a 50 mL flask, and citrate added dropwise until pH of ~3.5 is reached. The it was diluted with water to 50 mL mark. Absorption = 0.5775 and calculated Molarity = 0.000343.

The box I got the vitamin tablets from claimed 65 mg of iron so I believe it should be around that number somewhere. Thanks

Explanation / Answer

Let's assume, the vitamin tablet contains x g of iron (Fe)

Since, atomic weight of Fe is 55.85, so the vitamin tablet contains x/55.85 mol of Fe

According to the given question, it undergoes multiple dilution which are shown stepwise below.

1. "The tablet was boiled until dissolving in 25 mL of 6 M HCl, then it was filtered" ---> means x/55.85 mol of Fe that we started with now remains in that 25 mL solution.

2. "5 mL of the filtered solution taken for a volumetric flask dilution out of total 25 mL"

i.e. 25 mL solution contains x/55.85 mol of Fe

Hence, 5 mL solution contains x/55.85 * 5/25 mol of Fe.

3. Next "5 mL of the filtered solution was put into a 100 mL volumetric flask and diluted to 100 mL"

i.e. considering a homogeneous solution, 5 mL of the filtered solution containing x/55.85 * 5/25 mol of Fe is now contained in the 100 mL solution in the volumetric flask.

4. Next "5 mL of the more diluted solution was put into a 50 mL flask" i.e.

100 mL solution contains x/55.85 * 5/25 mol of Fe

So, 5 mL solution contains x/55.85 * 5/25 * 5/100 mol of Fe

5. Next, "it was diluted with water to 50 mL mark"

i.e. x/55.85 * 5/25 * 5/100 mol of Fe that contained in the 5 mL solution, now contained in 50 mL after dilution

i.e. 50 mL of the solution contains x/55.85 * 5/25 * 5/100 mol of Fe

Hence, 1000 mL of solution contains x/55.85 * 5/25 * 5/100 * 1000/50 mol of Fe

According to the definition of molarity, number of moles present in a 1000 mL solution is the molarity count

So, x/55.85 * 5/25 * 5/100 * 1000/50 = 0.000343

i.e. x/55.85 * 1/5 = 0.000343

i.e. x = 0.000343 * 5 * 55.85 = 0.0958 g = 95.8 mg

Hence, the vitamin tablet should contain 95.8 mg of Fe (the deviation from the actual value given most likely appears from the experimental error)

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