A 0.2481 g sample of marble was dissolved in 100 mL, and a 10.00 mL aliquot of the solution was titrated to an end point with 23.56 mL of 0.01052 M EDTA solution. What is the molecular weight?
I know how to start this problem. Any help is appreciated!
Why didn't you show what you know and let us help you from there?
M EDTA x L EDTA = moles EDTA.
moles EDTA = moles marble.
moles marble x molecular weight = grams.
Solve for molecular weight.
(0.01052 M EDTA)(.02356 L) =2.48 x 10^-4 mol EDTA or marble
2.48 x 10^-4 mol marble x _g/mol =0.2481g
molecular weight = 1000 g/mol
so I don't do anything with the 10-ml aliquot of soln?
Sure. Since it was a 10 mL aliquot, the moles in the original sample is 10 times the moles of the titration. Dividing your answer by 10 gets 100 for the molecular weight which is close. (Dividing you answer by 10 is the equivalent of multiplying the moles by 10.) Since you have four significant figures, you need one more place to the 100.something.
wouldn't the units be off? g/mol*ml
No.
mL EDTA x M EDTA = moles EDTA in 10 mL.
Moles EDTA in 10 x (100 mL/10 mL) = moles EDTA to titrate the original sample.
moles EDTA to titrate the original sample = moles marble in the original sample.
moles marble x molecular weight marble = grams marble.
thanks for the help DrBob222!
To find the molecular weight of the marble sample, we can use the concept of stoichiometry. The molecular weight is equal to the molar mass of the sample, which can be calculated by dividing the mass of the sample by the number of moles.
Let's solve this step by step:
1. Calculate the number of moles of EDTA used in the titration:
Moles of EDTA = Volume of EDTA solution (in L) × Concentration of EDTA solution (in mol/L)
Moles of EDTA = 0.02356 L × 0.01052 mol/L
2. Use the balanced equation between EDTA and the component in the marble sample to find the molar ratio:
According to the balanced equation, 1 mole of EDTA reacts with 1 mole of the component in the marble sample.
3. Calculate the number of moles of the component in the marble sample:
Moles of component = Moles of EDTA
4. Calculate the molecular weight of the component in the marble sample:
Molecular weight = Mass of sample (in g) / Moles of component
Now, let's plug in the values. Assuming the EDTA reacts with the calcium carbonate (marble), the balanced equation is:
CaCO₃ + EDTA → Ca(EDTA) + CO₂
Given:
- Mass of sample = 0.2481 g
- Volume of EDTA solution used in the titration = 23.56 mL = 0.02356 L
- Concentration of EDTA solution = 0.01052 mol/L
1. Calculate the moles of EDTA:
Moles of EDTA = 0.02356 L × 0.01052 mol/L = 2.477 × 10^(-4) mol
2. The molar ratio between EDTA and the component in the marble sample is 1:1.
3. Calculate the moles of the component in the marble sample:
Moles of component = 2.477 × 10^(-4) mol
4. Calculate the molecular weight of the component (marble sample):
Molecular weight = 0.2481 g / (2.477 × 10^(-4) mol)
Calculating this, we find the molecular weight of the component in the marble sample.