Determination of Cu in Brass

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Determination of Cu in Brass

• By Nayan Patel

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Molarity of Na2S2O3

• Sample Calculation
• Mass of Na2S2O3 5H2O 25 grams
• Mass of KIO3 0.6978 g
• Volume of KIO3 50 ml
• Volume of Na2S2O3 Titrated 38.10 ml
• O.6978 g KIO3 (1 mol KIO3) (1000ml) (50ml)
  6.521495e-4 mol KIO3
• (214.002g) (250ml) (1000ml)
• Molarity of KIO3
• 6.521495e-4 mol KIO3 0.0130429 mol/L
• 0.050 L

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Molarity of Na2S2O3

• Determine Moles of S2O32-
• 6.521495e-4 mol KIO3 (3 mol I3-) (2 mol
  S2O32-) 0.003912897 mol S2O32-
• 1 mol IO3- 1 mol I3-
• Trial 1
• 0.003912897 mol S2O32- 0.1029 mol/L S2O32-
• 0.038 L
• Trial 2
• 0.00391284 mol S2O32- 0.1043 mol/L S2O32-
• 0.0375 L
• Trial 3
• 0.00391284 mol S2O32- 0.1066 mol/L S2O32-
• 0.03675L

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Average, Standard Deviation and Relative Standard
Deviation

• Average (0.1029709737 0.10434 0.1066168937)/3
  0.1046 mol/L S2O32-
• Standard Deviation Formula
• S.D. (((.1046-.1026)2(.1046-.1043)2(.1046-.1066
  )2/(3-1)))(1/2)
• S.D 0.0018
• R.S.D. (0.0018/.1046)100 1.721

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Moles of Na2S2O3

• (Molarity of Na2S2O3 )(Volume Titrated) Moles
  Na2S2O3
• Moles of Na2S2O3 moles Cu
• 2 Moles of Na2S2O3 1 mole I3-
• Find moles of Na2S2O3
• Moles of Cu
• Moles I3-
• Grams of Cu

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Calculations

• (0.1046 mol/L of Na2S2O3)(.03530L) 0.00369238
  mol S2O3 2-
• 0.00369238 mol S2O3 2- 0.00369238 mol Cu
• 0.00369238 mol Cu (63.546 grams Cu) 0.24202 g
  Cu
• 1 mol Cu
• 0.00369238 mol S2O3 2- (1 mole I3-) 0.00184619
  mol I3- 2 mol S2O3
• Do This For Each Trial and Find mass of Cu in
  grams

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Wt/Wt Cu from Sample

• Trial 1
• 0.24202g Cu 100 79.638 79.6
• 0.3039 g Cu
• Trial 2
• 79.364 79.4
• Trial 3
• 78.349 78.3
• Average 79.638 79.364 78.349 79.11779.1
• 3
• S.D. 0.679 0.7

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Question?

• Given 0.00184619 moles I3-. Find grams of Cu?

ANSWER 0.00184619 moles I3- (2 moles S2O3 2-)
0.00369238 moles S2O32- 1 mol
I3- 0.00369238 moles S2O32- moles of Cu
(65.546 g/mol) 0.24202 grams Cu
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ANY QUESTIONS????

• PLEASE READ THE LABEL ON THE BOTTLE
• Susan was in chemistry. Susan is no more, for
  what she thought was H2O was H2SO4.
• Q Why do chemists call helium, curium and barium
  the medical elements? A Because if you can't
  helium or curium, you barium!