# Back Titration Of Metal Carbonate

• Lancelot59
In summary, I'm having an issue solving a back titration problem. We need to identify the metal in a metal carbonate. It can either be a group 1A or 2A element, but I don't know how to determine which. I think the equation should be: M2CO3 + 2HCL -> H2CO3 + 2MCL2, but I'm not sure how to solve for the number of mols of the anion in the main sample bucket. I'm dropping a 0 and hopefully that will work.
Lancelot59
I'm having an issue solving a back titration problem. We need to identify the metal in a metal carbonate. It can either be a group 1A or 2A

1.8500 grams of the carbonate are diluted to .2500L and then 0.02000L is taken and mixed with 0.01500L of 0.1789M HCl in a flask. After shaking the mixture around 0.01756 L of 0.1013M NaOH was used to titrate the remaining HCl.

I started this by first determining how many moles of HCl were added to the flask, and how much titrated with the NaOH:

0.01500L*0.1789M = 0.0026835 mol HCl total in flask
0.01756 L NaOH * 0.1013M x 1mol HCl/1mol NaOH = 0.001778828 mol HCl titrated.

So 0.000904672 mols of the HCl reacted with the metal carbonate. From here I would go to determine how many mols of the carbonate there are, but I'm not sure how to do that. Writing the equation could turn out two different ways becuase I don't know how the metals are grouped. Just picking one and running with it gave me a molar mass of about 3400...not good.

This is what I think the equation should be:
M2CO3 + 2HCL -> H2CO3 + 2MCL2

How can I solve this?

Ignore metal - it is just a spectator. Calculate number of moles of carbonate anion.

--

What do I use for a mole ratio though? If I just ignore the metal I came up with:

CO3-2 + 2HCL --> H2CO3 + 2Cl-

So using that setup:

0.000452336 mol HCL x 1mol CO3-2/2mol HCL = 0.000226168 mol CO3-2

Then since g=mols*molar mass --> molar mass = g/mols. The molar mass turns out to be 8179.760178. A bit much...

Perhaps there is something more, but seems like you forgot about dilution.

--

Right...oops. /facepalm

So there's 0.000226168 mol in 0.02000L, so 0.113084M x 0.250L = 0.028271 mols of the anion in the main sample bucket. So using that my molar mass is 65.4ish... well it's getting better at least. I'll do some more math and edit it in.

No, still not working. I dropped a 0. The molar mass I got was 327ish. I have no clue what's going wrong.

Last edited:

## 1. What is back titration of metal carbonate?

Back titration of metal carbonate is a laboratory technique used to determine the amount of a metal carbonate compound present in a sample. It involves reacting the sample with an excess of acid, and then titrating the remaining excess acid with a base to determine how much acid was used up in the reaction. This can then be used to calculate the amount of metal carbonate present in the sample.

## 2. When is back titration of metal carbonate used?

Back titration of metal carbonate is typically used when the metal carbonate compound is insoluble or reacts slowly with acid, making it difficult to determine the end point of a direct titration. It is also useful when the sample contains impurities that interfere with the direct titration process.

## 3. What equipment is needed for back titration of metal carbonate?

The equipment needed for back titration of metal carbonate includes a burette, pipette, conical flask, indicator solution, and standardized solutions of acid and base. A balance may also be needed to accurately measure the sample.

## 4. What are the potential sources of error in back titration of metal carbonate?

Some potential sources of error in back titration of metal carbonate include inaccurate measurements of the sample, the acid or base solutions, or the indicator solution. The reaction may also not go to completion, leading to an inaccurate determination of the amount of acid used. Additionally, human error in reading the burette or pipette measurements can also contribute to errors in the results.

## 5. What are the limitations of back titration of metal carbonate?

Back titration of metal carbonate has some limitations, including the fact that it is a time-consuming technique and requires multiple steps. It may also be less precise than direct titration methods. Additionally, if the metal carbonate compound is highly insoluble, it may not completely react with the excess acid, leading to inaccurate results.

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