Transcript TAHAP-TAHAP PEKERJAAN ANALISIS KIMIA

nd
3
Meeting
Chemical Analysis
Steps and issues
STEPS IN CHEMICAL ANALYSIS
1.
2.
3.
4.
Sampling
Preparation
Testing/Measurement
Data analysis
2. Error in chemical analysis
3. Statistics for chemistry
SAMPLING
Prerequisite: sample should be representative
Example:
Main sample
A
C
B
1
2
3
4
Bulk sample
a
b
a
b
c
d
c
d
2+3
Primary sample
1+4
Sub-bulk sample
Lab sample
Preparation for Solid Sample
1. Wet Digesting
• Direct solvation with water
• Solvation with: oxydator acids (HNO3, H2SO4,
HCl, HClO4, its mixtures) and base.
• Destruction with aqua regia: HNO3 : HCl = 1 : 3.
2. Dry digesting
Ashing (Furnace) in certain temperature
(+“ashing aid”. if necessary), solving in acids,
and diluting quantitatively
TESTING/MEASUREMENT
Purpose : Qualitative and quantitative
analysis
Qualitative Analysis: Spot test Analysis
Quantitative Analysis:
Conventional Methods: Volumetri dan
Gravimetri
Physico-chemical methods (modern) :
Elektrokimia, Spektrofotometri
Calculatioan and Data Interpretation
DATA CAN BE ACHIEVED
(quantitative analysis):
 volume, (volumetric),
mass, (Gravimetric)
Absorption (Spectrometric)
Potential Cell (Electrochem)
Should be
changed in to
Concentration,
(M, ppm)
content
(% mass/mass
, % vol/mass)
Error in data interpretation
Every steps in analysis steps
always face error.
Need Statistic
calculation to help in
decision making
Error in chemical analysis
1. Indeterminate Error
error can be exactly defined
Examples:
- Noise and deviation in electronic circuits
- Vibration of building
- environment change
2. Determinate Error/Systematical error
- Error in methods: Interfere agents ( can be + or -)
3. Operational Error: Operators/Analysts
4. Instrumental Error: Uncalibated/ un-standardized
instruments
Relative Error
True value – measurement value
% Error =
x 100%
True value
Simple Statistics in chemical analysis
1. Mean (harga rata-rata, x ),
x1 + x2 + x3 + ... + xn
X =
n
2. Standard Deviation (S), Variability of analysis result
 ( x – x )2
S=
n–1
JK
S=
n - 1
3. Relative Standard Deviation (R.S.D)
s
R.S.D =
x
4. Coefficient of Variation (C.V.)
s x 100
C.V. =
x
Example :
Analysis of iron ores produce % mass of Iron:
7,08 ; 7,21 ; 7,12 ; 7,09 ; 7,16 ; 7,14 ; 7,07 ; 7,14 ; 7,18 ; 7,11.
Calculate: means, Standard of deviation, and coefficient of variation !
Jawab :
X = 7,13 % ; s = 0,045 % ; C.V. = 0,63%
5. Batas Kepercayaan, merupakan daerah di sekitar harga yang
sesungguhnya
 = x + t (sx)
s
sx =
n
Nilai t diperoleh dari Tabel t pada derajat kebebasan (D.B.) = n - 1
Contoh:
Hasil analisis massa nikel (mg) yang terkandung dalam 1 g suatu bahan
galian adalah : 5,0 ; 5,3 ; 5,7 ; 4,8 ; 5,2
Hitung batas kepercayaan pada tingkat kepercayaan 95%
ANSWER
• x = 5,2 ; s = 0,3 ; sx = 0,134
•  = 5,20 + 0,37 So 95% believe that % mass of Iron is between : 4,83 –
5,57.
8.Presision
The similarity of value/data in one set of data,
shown by standard of deviation
9.
Acuration
The nearness of data measurement to
the true value
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B
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A
B
C
Keterangan:
A : Presisi baik, akurasi baik
B : Presisi baik, akurasi tidak baik
C : Presisi tidak baik, akurasi baik (rata-rata)
D : Presisi tidak baik, akurasi tidak baik
D
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