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Gravimetric Analysis of a Metal Carbonate

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Udit Modi

on 12 November 2013

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Transcript of Gravimetric Analysis of a Metal Carbonate

LAB GROUP: Udit, Nikita, Nishi, Haris, Masoumeh
The purpose of this lab is to determine the identity of a Group 1A metal carbonate using gravimetric analysis. The unknown substance is dissolved and added to a calcium solution which allows the carbonate ions to precipitate. This allows the identity of the metal to be known through some calculations.
November 1, 2013
Gravimetric Analysis of a Metal Carbonate
Question 1

Gravimetric Analysis of a Metal Carbonate
Irritant if it comes in contact with skin or eyes or is ingested or inhaled
Calcium Chloride is Stable
First Aid
Skin: Wash hand throughly with soap
Eyes: Use eyewash station
Inhalation: Move to fresh air; loosen clothes
Ingestion: Do not induce vomiting; loosen clothes
.01836 mole CaCO3
There are .01836 moles of Calcium Carbonate.
Question 2
The molar mass of the unkown substance is 107.4 g/mol.
Question 3
a. Lithium Carbonate - 73.89 g/mol
b. Sodium Carbonate- 105.99 g/mol
c. Potassium Carbonate- 138.21 g/mol
Question 4
The molar mass of the unknown substance is closest to that of sodium carbonate because 107.4 g/mol is close to 105.99 g/mol.
Question 5
The percent error is 1.330%. This is calculated by subtracting the observed value (107.4) from the actual value (105.99) and then dividing this by the actual value and multiplying by 100%.
Calcium Chloride
Unknown Carbonate Sample
Distilled Water
Bunsen Burner
Filter Funnel
Filter Paper
Glass Stirring Rods
Graduated Cylinder
Ring Stand and Iron Ring
Clay Triangle
Bunsen Burner
Use the bunsen burner to heat the crucible.
Add 2 grams of the substance and heat the crucible again to remove all moisture.
Add the substance with distilled water to a beaker and then pour in the calcium chloride solution.
Let the precipiate settle and then using filtering techniques, filter the precipitate.
Mass the precipitate and use this for calculations.
Question 3
The unknown carbonate is sodium carbonate, Na2CO3. The percent error is 4.8281%.
Question 4
The experimental sources of error that could cause the molar mass of the unknown substance to be too high would be that the sample of the unknown was not completely dehydrated. The experimental sources of error that could cause the molar mass to be too low would be that a small amount of the precipitate was left in the beaker after the filtration process was completed or the metal carbonate was over-dehydrated during the heating process.
The work is shown on the Calculations and Graphs section.
Question 1
There are 0.01683 moles of the precipitated calcium carbonate.
Question 2
The molar mass of the unknown carbonate is 111.11 grams per mole.
Experimental Sources of Error
The percent error is 4.8281%. Since only one trial was performed, the percent deviation cannot be calculated. Experimental sources of error may have occurred when handling the crucible. During the experiment, the crucible was heated three times, once to find the initial mass of the crucible and twice when heating the unknown metal carbonate. The cooling time of the crucible is crucial to the experiment; if the cooling periods after each time the crucible were heated are different, the mass would not be correct. Another experimental error could occur if the filter paper used during the filtration process has a hole in it; a hole will prevent the substance from separating from the liquid completely, resulting in an incorrect mass of the unknown carbonate. Also, if the substance is over-dehydrated and burned during the dehydration process, the result could alter the mass of the unknown carbonate. Likewise, if the substance is under-heated, the mass of the substance will be incorrect. If the experiment was to be repeated, things that could have been done differently would be keeping the cooling time of the crucible constant each time it was heated and avoiding over-dehydrating or under-heating the metal carbonate. This way, better precision could be obtained.
Discussion of Theory
In this lab, the law of definite proportions can be observed. The law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. This law is pertinent to NaCO3, which was the unknown carbonate. Another law observed was the law of conservation of mass. When the carbonate samples become anhydrous, the water evaporates into the air. The mass of the elements is conserved even though they enter different states. The purpose of this experiment was fulfilled because the unknown carbonate was identified. The experiment worked since we were able to form a precipitate by performing a double replacement reaction, and the measuring of that precipitate, along with calculations, allowed us to determine the identity of the unknown metal carbonate.
Our purpose had been to determine the identity of the Group1 metal in the metal carbonate and we were successful in doing so, proving that our metal carbonate was in fact sodium carbonate. The molar mass of the unknown compound turned out to be 111.11 g/mol which most accurately lined up with sodium carbonate’s 105.989 g/mol molar mass. Therefore we found our results with 95.1719% accuracy or in other terms, 4.8281% error. In order to achieve our goal, we had to perform a double replacement reaction with calcium carbonate We dehydrated the hydroscopic metal carbonate by heating it not once, but twice. Afterwards, the double replacement reaction was performed by mixing the metal carbonate with water and calcium chlorate. Precipitate was formed and by using the mass of the precipitate formed in the reaction, we were able to find the molar mass of the then unknown carbonate. Our technique involved the use of filter paper and a funnel to separate the precipitate from the rest of the solution. There were numerous sources of error which may have led to the percent error that we had. If we were to redo the experiment we could improve it by using better heating methods with the Bunsen burner, making sure we accurately record the mass measurements, and by using the best filter paper available to us
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