Experiment 4 : Determination OF THE Purity OF A Sodium Sulphate Sample BY Gravimetric Analysis PDF

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EXPERIMENT 4: DETERMINATION OF THE PURITY OF A SODIUM SULPHATE SAMPLE BY GRAVIMETRIC ANALYSIS

OBJECTIVE: Determine the concentration of sulfate ion gravimetrically by precipitation with barium chloride.

RESULTS: Mass of the sodium sulphate sample: 0.6070 g Mass of filter paper: 1.0654 g Mass of filter paper + precipitate: 2.0252 g

CALCULATIONS: 1. Calculate the mass of the BaSO4 precipitate obtained. BaSO4 = ( Mass of filter paper + precipitate ) - Mass of filter paper = 2.0252 g - 1.0654 g = 0.9598g

2. Calculate the actual mass of sodium sulphate in the sample.

actual mass of SO2-4 = weight of precipitate*gravimetric factor = 0.9598 * [( 2(23) + 32.06 + 4(16) ) / ( 137.33 + 32.06 + 4(16) )] = 0.9598 * (142.06 / 233.39) = 0.5842g

3. Calculate the purity of the sodium sulphate sample.

% purity of SO2-4 = weight of analyte/weight of sample * 100 = 0.5842g/0.6070g * 100 = 96.24%

DISCUSSION: The solution was digested to break the bonds in unknown sample to make the sulphate in the solution was free to precipitate with the BaCl2 to form BaSO4. The precipitate was filtered through a paper filter which was then ignited and completely ashed. The completeness of the precipitate was checked by adding BaCl2 to the clear solution on the surface of the precipitate, if there was no cloudiness forming then it indicated that there was no sulphate left out in the solution. Otherwise, excess BaCl2 must be added to precipitate the sulphate. So, in this experiment the mass of precipitate that obtained was 0.9598g. After that the actual mass of sodium sulphate was calculated as 0.5842g. There might be a few error in this experiment that lead the results to change. Foreign cations such as ferric iron, calcium and to a lesser extent, the alkali metals were coprecipitated as the sulfates. These were substitutional impurities and the magnitude of the error were depended on the differences between the weight of the foreign sulfate or oxide and the weight of equivalent amount of barium sulfate. The presence of ferric ion can produce errors as high as 2% in the determination. There are a few step can take as a precaution in this experiment to avoid errors. First the precipitate is digested to increase the average of particle size and reduce cop-precipitate. Second, BaCl2 is added slowly amidst effective stirring to reduce relative supersaturation. Next, completeness of the precipitation tested after each digestion by adding drops of BaCl2. Lastly, the container that contain BaSO4 washed with warm water to removed Cl- salt present.

CONCLUSION: The main aims of this experiment are clearly achieved. Thus, the results successfully determined the amount and concentration of the sulphate through the adopted method; gravimetry.

REFERENCES: 1. En. Zainal Kifli A.Razak, Faculty Of Applied Science, UITM Pahang. Basic Analytical Chemistry. 2. Khan Academy, 2015, Gravimetric analysis and precipitation gravimetry. Retrieved on 28th June 2020 from https://www.khanacademy.org/science/chemistry/chemical-reactionsstoichiome/limiting-reagent-stoichiometry/a/gravimetric-analysis-and-precipitationgravimetry.

3. Opoku Earnest, 2014, Determination Of Sulphate As Barium Sulphate Using Gravimetry With Drying Or Residue. Retrieved on 28th June 2020 from https://www.slideshare.net/Ernest13/determination-of-sulphate-as-barium-sulphate

4. Santa Monica College, 2020, Gravimetric Analysis (Experiment). Retrieved on 28th June

2020

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https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Laboratory_Experiments/Wet_ Lab_Experiments/General_Chemistry_Labs/Online_Chemistry_Lab_Manual/Chem_11_Exper iments/07%3A_Gravimetric_Analysis_(Experiment).

5. Ulrich De La Camp and Oliver Seely, Gravimetric Sulfate Determination. Retrieved on 28th June 2020 from http://chemistry.csudh.edu/oliver/che230/labmanual/gravsulf.htm....