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Gravimetric Analysis of a Metal Carbonate

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Srishti Me

on 24 November 2014

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Transcript of Gravimetric Analysis of a Metal Carbonate

Gravimetric Analysis of a Metal Carbonate
In this experiment, an unknown Group 1 metal carbonate, M2CO3, is analyzed to determine the identity of M. Such metal carbonate forms a precipitate with CaCO3; after recording the mass and calculating the formula weight, the identity of the Group 1 metal can be determined.

Calcium Chloride, 125 mL
Graduated Cylinder, 250-mL
Unknown Carbonate sample M2CO3, 2 g
Ring Stand and iron ring
Water, distilled, 200 mL
Balance Scale
Clay Triangle
Beakers 500 mL, 2
Watch glass
Bunsen Burner
Wired Gauze
Crucible tongs
Iron Gauze
Filter Funnel
Heat Resistant Glove
Filter paper
Wash bottle
Glass stirring rod

Calcium Chloride (CaCl2)
--Stability: stable
--First-Aid: If eye contact occurs, immediately remove any contact lenses and flush eyes with cold water for 15 minutes. If skin contact occurs, flush area with cold water and apply emollient.
--Hazards: Skin and eye irritant; slightly hazardous when in skin contact.

Distilled/Deionized Water (H2O)
--Stability: stable
--First-Aid: N/A
--Hazards: N/A

Pre Lab Questions
We begin the experiment by setting up the bunsen burner and brushing the crucible to decontaminate it. 2 grams of the unknown carbonate is then added and brushed by the flame for 2-3 minutes. After cooling and weighing it, this brushing is repeated one more time to insure the carbonate is anhydrous.

Procedures: Part 1
Once the weight is recorded the carbonate sample is added into a 400 mL beaker, filled with 200 mL of water. Mixing and crushing the carbonate within the water dissolves it into ions of 2M+ and CO3-. 125 mL of CaCl2 is added to create a precipitate through a double replacement reaction (M2CO3 + CaCl2 → 2MCl + CaCO3). The solution is poured through filter paper and using gravimetric filtration is separated entirely using distilled water.

Procedures- Part 2
By: Srishti B., Alexia H., Samad F., Marcin W.
The precipitate, CaCO3, is then dried and measured. That mass is converted into moles and then set equal to M2CO3, as it is in a 1-1 mol ratio equation. The grams measured of M2CO3 after the crucible is burned is then divided by the moles to get the grams per mol answer.

Procedures: Part 3

Mass of Crucible (g) 21.9125 g
Mass of Crucible + M2CO3 23.9075 g
Mass of Crucible + M2CO3(dry) 23.5642 g
Mass of Crucible + M2CO3(2nd dry) 23.5627 g
Mass of M2CO3 1.6502 g
Mass of Filter Paper 0.8926 g
Mass of Filter Paper + CaCO3 2.4343 g
Mass of CaCO3 1.5417 g
Moles of CaCO3 0.01540 mol
Molar mass of M2CO3 107.2 g/mol
Identity of M2CO3 Na2CO3
Percent Error 1.13% error

Data Table A: Recordings and Calculation Results
After finishing all of the calculations, a molar mass for M2CO3 of 107.2 g/mol was received. Since this is very close to the sodium carbonate, Na2CO3, molar mass, it is safe to assume that M is sodium and M2CO3 is sodium carbonate. This also agrees with the white color that the solid was found in through the experiment, as Na is known to be a silvery-white.

Post Lab Questions
1. There were .01540 moles of CaCO3 precipitated

2. The molar mass of the unknown carbonate was 107.2 g/mol

3. The unknown element (M) was found to be Sodium, Na. The percent error was 1.13%

4.Errors were listed before this slide.

One theory exhibited in the experiment is the law of conservation of mass. When the carbonate sample is heated to become anhydrous, water evaporate into the air. Even though the matter changed states, the mass was preserved, allowing the mass of the product to be found in order to determine its composition. Another theory employed in this lab is the law of definite proportions. Since samples of a compound will always have the same ratio, this law helped in figuring out the unknown part of the given carbonate.

Discussion of Theory
Experimental Sources of Error
Throughout the experiment, several errors could have occurred to hinder the process. A loss of mass may have happened since the method of outdoor cooling was used, some of the substance may have blown away, or because of spills when removing the filter paper from the watch glass which would increase the molar mass. Before this, overheating/ burning of the Na2CO3 may have happened, as black specks were found upon examination of the product.

A variation in the amount of product was also possible, due to the fact that the graduated cylinder had increments of only 10mL. Lastly, the lack of time meant that the filter paper of product was only able to be weighed once, without breaking the clumps apart, resulting in mass uncertainty, which was most likely a higher mass than if we weighed it another time.
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