Michael Thomas Harbuck						Determination of the Molar Mass of an Acid by Titration 
CHEM 2045C  29-09-2007									Lab Report
Mrs. Deo

I.  Titration Lab

II.  The purpose if this titration laboratory experiment is the standardization of a 
solution of NaOH, and determination of the molar mass of an unknown Acid, a solid using the titration methods being learned at the same time.  This experiment involves several new laboratory techniques which must be practiced in step before the actual titration of the unknown.  The secondary 	purpose of this experiment is to hone the  previously learned lab skills, as well as developing the newly introduced chemical analysis tools.

III.  Part I - Standardization of Sodium Hydroxide
The procedure for this experiment required first and foremost, that a know solution of sodium hydroxide is created, and then standardized for use within the titration of the unknown acid (aq).   The prelab calculation determined that the required amount in	grams of sodium hydroxide to prepare 500ml of approximately 0.10 Molar solution to be 2.0 grams of sodium hydroxide (s).  
Being severely hydroscopic, non analytical scales are used to prepare the base solution, where after this solution will be standardized accordingly.  Important is the safe keeping of the prepared solution in a non reactive vessel which does not allow reaction with any 	elements in the air.  The weighed 2.0g NaOH is placed into a 500ml beaker, and deionized water is added up to the half liter mark. This solution is stirred thoroughly and then stored in a plastic container with an air tight cap.  
	 
For the second part of the experiment this solution which has been prepared above must be standardized using the titration method
on a  known substance to determine the stoichiometrically derived molarity of the NaOH solution.  This is effected as follows. The titration equipment was set up using a ring stand bearing the holder for the burette.  A glass funnel, 50ml beaker, and one 250ml Erlenmeyer flask completed the setup.   The burette was rinsed with the app. 0.1 Molar NaOH solution.  The burette was filled with approximately 50ml of the NaOH from stock, taking care to fill from a smaller vessel and glass funnel for safety purposes. This start amount in the burette is recorded for further use. The first standardizing sample of KHP of (0.8466g KHP), having been weighed to four significant figures, was added to the 250ml Flask.  Deionized water in the smallest amount which dissolved all of the solid is added to the flask.  This is manually but gently shaken to ensure dissolution. To the KPH solution three drops of the organic indicator phenolphthalein is added.  The titration is started.  At first the amount from the burette is rather large, then, as the base indicator color change becomes more difficult to stir away the titration is performed very slowly drop by drop.  With the last drop of NaOH, the titration end with the solution being a light pink color thorough the entire solution.  The end volume of the burette is read and noted down.  This titration is performed another four times, each with a different amount of appr. 0.8g of the KHP having been analytically weighed.  

Data from the standardization of the NaOH.
	
			Trail I		Trail II	Trail III 	Trail IV	Trail V
	
Mass of KHP(g)	.8466		.8766		.8094		.8678		.8092
Final Burette(ml)	49.23		43.50		40.71		42.15		38.43
Initial Burette(ml)	9.27		4.20		3.41		2.30		2.28
Total NaOH (ml)	40.20		39.30		37.29		39.85		36.10
Calculated 
	Molarity	0.1036	0.1055	0.1063	0.1066	0.1097

	The ratio of acid to base is one to one in standardization.  With the mass of KHP calculated from the mass used in the experiment, 	and knowing the molecular weight of the KHP, the molar mass can be derived.  From the molar mass and the volume of the base 	used to the point of equilibrium, the molarity of the acid can be found, which equals the molarity of the base used.  

	After five samples were titrated the average of the five trails was a molarity of base 0.1063 M NaOH, which corresponds very close
	to the goal molarity of 0.1 M NaOH.

Part II - Molar Mass of an Unknown Acid - Sample Number 56

The second part of this experiment was performed on the following lab day, and all of the preparations as far as equipment is concerned are identical.  There was a discrepancy with the second trail as to the first, because the first trial was completed in the first lab session, and the second in the following.  The liquid residue from the previous wash affected the result of the second trial, causing what is know in German as an Ausreisser.  Therefore the average is only from the first and last, or third, trial regarding the Molar Mass of the Unknown Acid.  

Data from the Molar Mass of the Unknown Acid - Sample Number 56:

			Trail I		Trail II	Trail III
Mass of Sample(g)	0.3751	0.1326	0.1535
Final Buret(ml)	49.71		21.29		34.59		
			26.43	 	
Initial Buret(ml)	2.59		1.61		21.29		
			18,72
Total NaOH(ml)	54.83		19.68		13.3
	used	
Calculated Molar	64.36		108.0		73.0
	Mass(g)

	The calculations are as follows.  The known (average) Molarity of the Base 0,1063 M is multiplied by the known volume 
	0.05483 Liter to yield n=5.828 x 10-3 Mols of Base/Acid.    

	The known mass of the unknown sample #56 0.3751g is divided by the 5.282 x 10-3 Mols to yeild the derived Molar Mass.

	The derived MM of trail I is:  64.36 g/Mol
	_______________________________________________________________
	
	The average MM found using the first and third trials was 68.70 g/mol for the MM of the unknown acid.

V.  Conclusion:  Titration is a fun and fairly accurate method for proving the Molarity 
	of known and unknown substances, acids, and bases.  
The process does rely on the indicator, which is the key to the  titration.  There are new very small and very accurate power of Hydrogen meters which can be used instead of the organic indicator which changes conformation with the changing pH.  It would be interesting to test the accuracy of these devices against the titration methods.  Deionized water must be used at ALL times.  Glassware should be washed and or rinsed before each lab  to ensure consistency and validity of the derived data.  The small 50ml beaker should be used to fill the burette, so as to avoid the possibility of spillage of the entire stock NaOH solution.   The mathematics and calculations must be practiced often to be learned and retained.