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In order to prepare a sample for absorbance readings, a vitamin tablet containing 25 mg of iron was dissolved in 6M HCl, quantitatively transferred into a 100 mL volumetric flask and diluted to the 100 mL mark with DI water. Then 20 mL and 17 mL of this solution were pipetted into separate 100 mL volumetric flasks and each of these was brought up to 100 mL volume by diluting with DI water to the mark.

Required:
Calculate concentration of iron in mg/L in each of these flasks

Respuesta :

Answer:

C₂ = 50 mg/L

C₃ = 42.5 mg/L

Explanation:

To do this, we just need to use the following expression:

C₁V₁ = C₂V₂     (1)

Where:

C₁: Original concentration of the Iron solution (mg/L)

V₁: aliquot of the iron solution (mL or L)

C₂: Concentration of the iron after beind dilluted (mg/L)

V₂: Volume of the flask that's being used.

Using the above expression, we just solve for C₂:

C₂ = C₁V₁ / V₂   (2)

We have the required volumes, but we do not have the concentration of the iron solution (C₁). To determine this, we use the initial flask of 100 mL and the mass of the iron:

C₁ = 25 mg / 0.1 L = 250 mg/L

With this value, we can replace in (2) to get the concentration on each flask.

Flask 1:

We have an aliquot of 20 mL, and it was dilluted to 100 mL, the concentration would be:

C₂ = 250 mg/L * (20/100)

C₂ = 50 mg/L

Flask 2:

We have an aliquot of 17 mL dilluted to 100 mL so:

C₃ = 250 * (17/100)

C₃ = 42.5 mg/L

Hope this helps

mickymike92

The concentration of iron in mg/L in each of the two flasks is 50 mg/l and 42.5 mg/L respectively.

The initial concentration of iron in the sample is obtained as follows:

A vitamin tablet containing 25 mg of iron is dissolved in 6M HCl and then made up to 100 mL in a 100 mL volumetric flask with DI water.

Concentration of iron in the solution = 25 mg/ 100 mL

Converting to mg/L; 1 L = 1000 mL, then 100 mL = 1000 * 1 L/ 1000 mL = 0.1 L

Concentration of iron in the solution in mg/L = 25 mg / 0.1 L = 250 mg/L

Then 20 mL and 17 mL of this solution were pipetted into separate 100 mL volumetric flasks and each of these was brought up to 100 mL volume by diluting with DI water to the mark.

Using the dilution formula C₁V₁ = C₂V₂ to determine the concentration of iron in each of these flasks:

C₁ = initial concentration; V₁ = initial volume

C₂ = final concentration; V₂ = final volume

Flask 1:

C₁ = 250 mg/L, V₁ = 20 mL, C₂ = ?, V₂ = 100 mL

C₂ = C₁V₁ / V₂

C₂ = 250 * 20 / 100

C₂ = 50 mg/L

Flask 2:

C₁ = 250 mg/L, V₁ = 17 mL, C₂ = ?, V₂ = 100 mL

C₂ = C₁V₁ / V₂

C₂ = 250 * 17 / 100

C₂ = 42.5 mg/L

Therefore, the concentration of iron in mg/L in each of the two flasks is 50 mg/l and 42.5 mg/L respectively.

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