Analytical%20Gravimetric%20Determination

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Analytical Gravimetric Determination

• Suh Kwon

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Purpose

• To measure the number of a given substance in a
  solution by precipitation, filtration, drying,
  and weighing
• Approximating the amount of SO42- ions in a
  sample of alum, KAl(SO4)2 12H20

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Background Information

• Gravimetric analysis is used to determine the
  amount of a substance by finding its mass, and
  then using the mass to find the quantity of the
  substance
• Example to find the measurement of solids
  suspended in a water sample, a known volume of
  water is filtered and the collected solids are
  weighed

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For this experiment

• The precipitate that will be formed in this
  experiment is barium sulfate, BaSO4
• Forms very fine crystals

• Beforehand, calculate how much 0.200 M Ba(NO3)2
  you would need to totally precipitate all of the
  sulfate ion present in solution

http//www.jinyakc.com/jy/My20Pictures/9.jpg
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!!!

• Make sure you add twice the calculated amount of
  Ba(NO3)2 because for every 1 mole of alum, there
  are 2 moles of Ba(NO3)2
• KAl(SO4)2 12H2O 2Ba(NO3)2 ? KNO3 Al(NO3) 3
  2BaSO4 12H2O

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Materials

• Buchner Funnel
• A piece of Whatman No. 42 filter paper
• Filter flask
• 1.059 g of alum compounds
• 50.0 mL of distilled water
• 22.3 mL (calculated) of 0.200 M Ba(NO3)2
• Heating Plate
• Analytical Balance
• Drying oven set at 50C

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An analytical balance is an instrument that's
used to measure mass at a very high degree of
precision.
Filter Flask
Analytical Balance
http//www.usdoj.gov/dea/photos/lab/analytical_bal
ance_mettler_ae-260.jpg
http//www.laboratoryequipmentworld.com/gifs/filte
r-flasks.jpg
Filter Paper
Buchner Funnel
http//upload.wikimedia.org/wikipedia/commons/5/52
/Buchner_funnel.jpg
http//www.isss.biz/prodImages/Whatman-Filter-Pape
r-Grade-2.jpg
http//www.rickly.com/sai/images/BUCHNER.JPG
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Procedures

• Dissolve the 1.059 g of alum in the 50.0 mL of
  distilled water
• Add twice the amount of 0.200 M Ba(NO3)2 to alum
  solution, stirring constantly
• Heat this solution for 15 minutes and allow the
  solution to stand overnight
• Next Day You will discover that fine crystals
  had appeared in the solution

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Procedures (2)

• 4. Weigh the filter paper separately and
  determine its mass on the analytical balance
• 5. Filter the solution through the Buchner
  funnel, containing the filter paper to collect
  the crystals
• 6. Remove the filter paper and allow it to dry in
  the 50C drying oven
• 7. Weigh the paper and crystals together and
  determine their total mass

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http//www.creative-chemistry.org.uk/activities/im
ages/buchner.gif
http//depts.washington.edu/chem/courses/labs/162l
abs/images/PA230280.JPG
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Data

• INITIAL
• Mass of alum 1.059 g
• Volume of distilled water 50.0 mL
• Amount of 0.200 M Ba(NO3)2 22.3 mL
• COLLECTED
• Mass of filter paper (alone) 1.675 g
• Mass of filter paper filtered crystals 2.715 g

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Equations

• Balanced Chemical Formula
• KAl(SO4)2 12H2O 2Ba(NO3)2 ? KNO3
  Al(NO3) 3 2BaSO4 12H2O
• Ba2 SO42- ? BaSO4 (s)
• Sulfate (Mass of Sulfate/Mass of Sample)
  100
• Percent Error (Theoretical Value Actual
  Value) 100
• Theoretical Value

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Calculations

• How much 0.200 M Ba(NO3)2 would be needed to
  totally precipitate all of the sulfate ion
  present in the alum solution
• 1.059 g alum 1 mol of alum 2 mol Ba(NO3)2
  1 L of Ba(NO3)2 1000 mL 22.3 mL
• 474.46 g alum 1 mol of alum
  0.200 mol Ba(NO3)2 1 L

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• The percent of sulfate ion in the alum based upon
  the experiment
• 2.715 g filter paper barium sulfate
• 1.675 g paper
• 1.040 g BaSO4
• 1.040 g BaSO4 1 mol BaSO4 1 mol SO42-
  96.04 g SO42- 0.4281 g SO42-
• 233.37 g BaSO4 1 mol BaSO4 1
  mol SO42-
• sulfate 0.4281 g SO42- 100
  40.43
• 1.059 g alum

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• The theoretical of sulfate ion in the alum
• 192.08 g SO42- 100 40.48
• 474.46 g alum
• The percent error in this investigation
• error 40.43 40.48 100 -0.15
• 40.48

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Conclusion

• With the help of this experiment, you were able
  to find the amount of sulfate ions in a sample of
  alum compound, comparing that value to the
  theoretical amount necessary
• A negative percent error signifies that there was
  a production of a solid throughout the reaction