1. Determination of Cu in Brass
By: Nayan Patel

2. Molarity of Na2S2O3 Sample Calculation Mass of Na2S2O3 5H2O = 25 grams
Mass of KIO3= g
Volume of KIO3 =50 ml
Volume of Na2S2O3 Titrated = ml
O.6978 g KIO3 * (1 mol KIO3) * (1000ml) * (50ml) = e-4 mol KIO3
( g) (250ml) (1000ml)
Molarity of KIO3
e-4 mol KIO3 = mol/L
0.050 L

3. Molarity of Na2S2O3 Determine Moles of S2O32-
e-4 mol KIO3 * (3 mol I3-) * (2 mol S2O32-) = mol S2O32-
1 mol IO mol I3-
Trial 1
mol S2O32- = mol/L S2O32-
0.038 L
Trial 2
mol S2O32- = mol/L S2O32- L
Trial 3
mol S2O32- = mol/L S2O32- L

4. Average, Standard Deviation and Relative Standard Deviation
Average= ( )/3 = mol/L S2O32-
Standard Deviation Formula
S.D.= ((( )2+( )2+( )2/(3-1)))^(1/2)
S.D=
R.S.D. = (0.0018/.1046)*100 =1.721%

5. 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

6. Calculations
( mol/L of Na2S2O3)(.03530L) = mol S2O3 2-
mol S2O3 2- = mol Cu
mol Cu * ( grams Cu) = g Cu
1 mol Cu
mol S2O3 2- * (1 mole I3-) = mol I mol S2O3
Do This For Each Trial and Find mass of Cu in grams

7. Wt/Wt % Cu from Sample Trial 1 0.24202g Cu * 100 =79.638 %=79.6%
79.364%= 79.4%
Trial 3
78.349%= 78.3%
Average= =79.117%=79.1% 3
S.D. = = +0.7

8. Question? Given 0.00184619 moles I3-. Find grams of Cu? ANSWER
moles I3- * (2 moles S2O3 2-) = moles S2O32-
1 mol I3-
moles S2O32- = moles of Cu* ( g/mol) = grams Cu

9. 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!