I had to do a complexation titration to calculate the concentration of aluminium. In this, 24.9274ml of EDTA was titrated against 0.0111129 M Zn standard solution, which took 39.45 ml of the Zn solution for the colour change.
Next 25 ml of an Aluminium solution was added to a 250 ml flask with 50ml of EDTA before being titrated with the Zn standard again. I got two different volumes for this second step with one being 41.4ml and the other 38.7 ml.
I would appreciate some help in understanding how to calculate the Al concentration from this.
To calculate the concentration of aluminum (Al) in the solution, you need to use the concept of complexation titration and stoichiometry.
In the first step, you titrated 24.9274 ml of Ethylenediaminetetraacetic acid (EDTA) against the 0.0111129 M zinc (Zn) standard solution. The volume of Zn solution required for the color change was 39.45 ml. From this, we can determine the moles of Zn that reacted with the EDTA in the first step.
To calculate the moles of Zn, you can use the formula:
Moles of Zn = volume of Zn solution used (in liters) * concentration of Zn solution
Given that the volume of Zn solution used is 39.45 ml (or 0.03945 L) and the concentration of Zn solution is 0.0111129 M, we can plug in the values:
Moles of Zn = 0.03945 L * 0.0111129 M
Next, in the second step, you added 25 ml of the aluminum solution to a 250 ml flask containing 50 ml of EDTA solution. Then, you titrated this mixture with the Zn standard solution, obtaining two different volumes: 41.4 ml and 38.7 ml.
To calculate the concentration of Al, we need to determine the change in moles of Zn in the second step compared to the first step. The difference in volume between the two trials is due to the presence of Al, which complexed with EDTA and prevented some Zn from reacting.
To find the moles of Zn in the second step, you can use the formula mentioned earlier:
Moles of Zn = volume of Zn solution used (in liters) * concentration of Zn solution
For the first trial, where the volume of Zn solution used was 41.4 ml (or 0.0414 L), we can calculate the moles of Zn as:
Moles of Zn (Trial 1) = 0.0414 L * 0.0111129 M
Similarly, for the second trial, where the volume of Zn solution used was 38.7 ml (or 0.0387 L), we can calculate the moles of Zn as:
Moles of Zn (Trial 2) = 0.0387 L * 0.0111129 M
After determining the moles of Zn in both trials, we need to subtract the moles of Zn in the first step from the moles of Zn in the second step. The difference in moles corresponds to the moles of Zn that reacted with the Al in the second step.
Finally, we can use the stoichiometry of the reaction between Al and Zn to calculate the concentration of Al. The balanced chemical equation for the reaction can provide the stoichiometric coefficients required for the calculation.
For example, let's assume the balanced equation is:
Al + Zn(EDTA)2- → Zn + Al(EDTA)2-
If the stoichiometric coefficient of Zn in the equation is 1, that means 1 mole of Zn reacts with 1 mole of Al. Therefore, the moles of Al can be determined by:
Moles of Al = Difference in moles of Zn in second step * Stoichiometric coefficient of Al
From the obtained moles of Al, you can calculate the concentration of Al by dividing the moles of Al by the volume of the Al solution used (25 ml in this case).