Determine the concentration of Mg2+ (in mmol/L) in the unknown solution (Note: details and additional information to solve the problem are provided in your lab manual):
Mass of EDTA: 0.606 g
Volume of EDTA used in titration (step 1): 10.48 mL
Volume of EDTA used in titration (step 2): 5.64 mL
FW of EDTA: 372.25 g/mol
The lab manual says: Accurately weigh out 0.6 g and dissolve it with gentle heating in 400 mL of water in a 500 mL volumetric flask. Gentle heating is best accomplished by standing the flask in hot water, not placing it directly on a hot plate. Cool to room temperature, dilute to the mark, and mix well.(in regards to EDTA)
I am completely lost I have tried multiple times and have gotten no where near the right answer (I know what it should be)...any help would really be appreciated.
The details you give from the lab manual are for the calculation of the molarity of the EDTA solution.
M = moles/L.
moles = grams/molar mass (formula weight) and you have all of that information. Then divide moles/0.500 L = molarity.
Regarding the remaining part of the problem, what did you use as an indicator and how was the "double" titration done?
The indicator used was Eriochrome Black T, and for the double titration... I don't know. I know that NaOH was added to precipitate Mg(OH)2, and then it was titrated with EDTA. Then it was left to sit for 5 minutes to dissolve any precipitated Ca(OH)2, and titrated again to go back to endpoint color.
To determine the concentration of Mg2+ in the unknown solution, you need to perform a titration using EDTA (ethylenediaminetetraacetic acid) as the titrant. The titration involves the reaction between Mg2+ and EDTA in a 1:1 stoichiometric ratio. By determining the amount of EDTA required to completely react with the Mg2+, you can calculate the concentration of Mg2+ in the solution.
Let's break down the steps to solve this problem and calculate the concentration of Mg2+:
Step 1: Prepare the EDTA solution
According to the lab manual, you need to dissolve 0.606 g of EDTA in water in a 500 mL volumetric flask. Follow this procedure carefully:
1. Accurately weigh out 0.606 g of EDTA.
2. Dissolve the weighed EDTA in 400 mL of water in the 500 mL volumetric flask.
3. Gently heat the flask by placing it in hot water until the EDTA is completely dissolved.
4. Once dissolved, cool the flask to room temperature.
5. Dilute the solution to the mark on the volumetric flask with water.
6. Mix the solution well to ensure homogeneity.
Step 2: Perform the titration
You will perform a titration to determine the amount of EDTA required to react with the Mg2+ in the unknown solution. Follow these steps:
1. Pipette a 10.48 mL aliquot of the unknown solution into a clean flask or beaker.
2. Add a few drops of the indicator solution (typically a metal ion indicator, such as Eriochrome Black T), which will change color when the Mg2+ is completely complexed with EDTA.
3. Slowly add the EDTA solution from step 1 to the aliquot of the unknown solution while constantly stirring until the color change occurs.
4. Note the volume of EDTA solution required for the color change. In this case, it is 5.64 mL.
Step 3: Calculate the concentration of Mg2+
To calculate the concentration of Mg2+ in the unknown solution, use the following formula:
Concentration of Mg2+ (mmol/L) = [(Volume of EDTA solution used) × (Molarity of EDTA solution)] / (Volume of aliquot used)
1. Calculate the molarity of the EDTA solution:
- Determine the number of moles of EDTA: 0.606 g / 372.25 g/mol = 0.00163 mol
- Calculate the molarity: 0.00163 mol / 0.5 L = 0.00326 mol/L
2. Calculate the concentration of Mg2+:
- Concentration of Mg2+ = [(5.64 mL) × (0.00326 mol/L)] / (10.48 mL) = 0.00175 mol/L
Therefore, the concentration of Mg2+ in the unknown solution is 0.00175 mol/L, or 1.75 mmol/L.
Make sure to double-check your calculations and that you followed the steps accurately.