Michael Thomas Harbuck						Empirical Formula Lab Report
CHEM 2045C  29-09-2007
Mrs. Deo

I.  Empirical Formula Lab

II.  The purpose of the empirical formula laboratory experiment is to gain practice in
determining the empirical and then chemical formula of 
a compound of Tin (SN) and Iodine (I).  Another of the mathematical skills learned and put to use practically within this laboratory
experiment is the percent yield calculation, being the actual yield of compound divided by the theoretical yield multiplied by 100
percent, which gives a percentage of compound produced as to the theoretical yield.  General laboratory skills are also still being acquired and practiced, and as always safety is of foremost importance.  

III. A. The procedure for the lab begins with the weighing of a sample of pure
	elemental Tin (Sn) in solid form.  The weight of the sample
being between 1 and one-half and two grams.  This is accomplished with an analytical scale, which gives the weight of the sample to   
four decimal places, or five significant figures.  Secondly, a sample of elemental Iodine in solid form is weighed.  Care must be taken to use a watch glass as the amount, once again between one and one-half and two grams, is weighed on the same analytical scale.  The next step after having recorded the masses of both samples, is to place both together in a 250ml Erlenmeyer Flask.
Approximately 35ml of an organic solvent, here naphthalene, is added to create a heterogeneous mixture.  The reflux apparatus for the heating and collection of the solvent must be set up.  A ring stand is used to hold both the 250ml flask containing the reagents with heating mantle, as well as the reflux cooling coil attached to the top of the flask, is erected.  The cooling coil of the condenser is supplied with a supply of cooling water, and last but not least the heating mantle is brought under the flask.  The reaction is allowed to run for a minimum of one half of an hour.  At the end of the allotted time period, the apparatus is turned
	off, and the reagent flask is allowed to cool.  

   B.  After the solution has cooled, the precipitate which has formed in the flask
must be removed using a rubber spatula and no more
than 35ml of the naphthalene as a rinse,  being filtered as it is poured through a pre-weighed filter paper into another receptacle.  The rest of the reactant Sn must be weighed and recorded.  (Weighing the filter paper at this step is not absolutely necessary, because the remainder of the Tin is large enough to be removed without fear of losing any of the reactant in the filter paper.  The flask containing the solution is then chilled in a water/ice bath.  Agitating the solution facilitates the faster precipitation of the new product.  (Tin Iodide).  Now filter the solution through a weighed filter paper, and allow the solvent to evaporate from the paper.  After full evaporation,  weigh the filter and precipitate, subtracting the weight of the paper to obtain the mass of the precipitated ionic salt.  

IV.  The acquired amounts, data and variables are as follows. 
		
	1.  The mass of the Iodine reagent		1.5580 g I
	2.  The moles of this Iodine Mass			1.228 x 10 to the negative
    second power Mols of Iodine
	3.  The mass of the Tin reagent at start		1.6776 g Sn / (1.413 x 10/-2
Mols Sn)
4.  	                          at end		1.3374 g Sn
	5.  The mass of Tin used in the reaction		0.3402g Sn 
	6.  The moles of the Sn used in the reaction	2.866 x 10 to the negative third
power Moles of Sn

	7.  The ratio of the moles of I to moles of Sn	4:1
	8.  Empirical Formula of the new compound	SnI4 (subscript 4)
	9.  The name of the compound			Tin Tetraiodide
		
	10.  Mass of the derived compound and paper	1.7403 g
	11.  Mass of the filter paper			0.9070 g
	12.  Mass of the derived compound		1.6430 g SnI4
		
	13.  Actual Mass of Sn in the Precipitate		.3114 g Sn (2.623 x 10/-3)
	14.  Actual Mass of I in the Precipitate		1.332 g I (1.050 x 10/-2 Mols I)
		
	15.  Percent of Sn used				18.6 %
		Percent of Sn used in Precipitate		91.4 %
	16.  Percent of I used				85.0 %
		Percent of I used in Precipitate		100 %		

	17.  Percent Yield					18.6 %

* Please see the informal lab report for the complete mathematical breakdown of the stoichiometric calculations

V.  Conclusion:
	The length of time as well as the temperature of the reflux apparatus is a great influence on the speed of the reaction.  It appears that the reaction reaches equilibrium, thus not allowing more actual yield to be produced.  The concentration of the the reactants is also a heavily weighted variable. From a purely mechanical aspect of the reaction, there seemed to be some precipitate which was small enough in particle size to pass through the filter paper.  Vigorously agitating the flask produced the precipitate much faster, and could be theorized in greater quantity.  It is to question whether or not a lower temperature would facilitate more precipitate.  Others who performed the same lab were not actively agitating their reagent flask upon cooling.  This formal lab corrects mistakes made in the laboratory notebook.     	
	Of the Sn used in the reaction, 91.4 percent was retained in the precipitate.  The results are as follows.  Using the amount of Sn
used in the reaction this comes to 2.866 Mols Sn. (0.3402 g Sn).  Now it can be checked with the precipitate to compare the theoretical amount of Tin to the actual amount in the compound of Tin Iodide.  If the Chemical formula of the Tin(II)Iodide is two Iodine molecules to every one of Tin, than the molar mass of the compound is 372.51 g /Mol Tin(II)Iodide. To  find the actual mass of the Tin in the compound multiply the total mass of the precipitate (1.643 g SnI?) by the number of moles of Tin in the formula 	for the Tin Iodide (1) by the molar mass of Tin (118.710 g/mol) and then divide by the molar mass of the SnI2 which is seen above as (372.51g/mol SnI2).  This gave the mass of the Tin in the precipitate as (0.52358 g Sn) and should have matched the known 	used amount (0.3402 g Sn).  Being a large difference, it was then calculated using the molar mass of the Tin Tetraiodide (626.31 g/Mol Tin(IV) Iodide.  The result here was (0.3114 g Sn).  These two number are much closer to each other, thus leading to the conclusion that the chemical formula of the compound is one mole of Tin to four moles of Iodine.  Therefore one Tin atom bonded to four Iodine atoms per molecule of Tin Tetraiodide.   Dividing the actual used total tin in Solution and precipitate by the start amount, and then multiplying by 100 gives the amount of tin used in the reaction as (20.3 percent Sn) of the original (1.6776 g Sn).  Out of this 20.3 percent, 10 percent is not accounted for in the final product mass.    
	Subtracting the actual stoichiometrically calculated amount of Tin (0.3114 g Sn ) from the actual precipitate yield (1.643 g SnI4) gives the actual mass of the Iodine in the actually yielded compound (1.332 g I).  This calculates to (1.0493 x 10/-2 Mol I).  If the 	amount of Iodine in the solution at the start was (1.228 x 10/-2 Mol I) , then (85.0 percent I) of the available Iodine was used in the reaction.   Using the same calculation as from above, the actual mass of the Iodine in the precipitate can be derived.  The mass of the precipitate (1.643 g SnI4) times 4 Mols of Iodine required for the reaction of each Mol of Sn by the Molar Mass of Iodine 	(126.9 g/Mol I) divided by the Molar Mass Tin Tetraiodide (626.31 g /Mol) gives exactly (1.332 g I) in the precipitate.
	The percent yield as seen from the view point of the Tin is as follows.  The starting Mols of Sn is (1.413 x 10/-2 Mols Sn).   The actual Mols in precipitate is (2.623 x 10/-3 Mols Sn).  The actual in precipitate divided by the Mols of Tin at the start times 100 percent gives (18.6 percent).