3 nd Meeting Chemical Analysis Steps and issues

STEPS IN CHEMICAL ANALYSIS 1. Sampling 2. Preparation 3. Testing/Measurement 4. Data analysis 2. Error in chemical analysis 3. Statistics for chemistry

SAMPLING Prerequisite: sample should be representative Example: Main sample AB C Primary sample dc b a a b c d Bulk sample Sub-bulk sample Lab sample

Preparation for Solid Sample 1.Wet Digesting Direct solvation with water Solvation with: oxydator acids (HNO3, H 2 SO 4, HCl, HClO 4, its mixtures) and base. Destruction with aqua regia: HNO 3 : HCl = 1 : 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)

Every steps in analysis steps always face error. Need Statistic calculation to help in decision making Error in data interpretation

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 ), x 1 + x 2 + x x n 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 (s x ) s s x =  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 ; s x = 0,134x = 5,2 ; s = 0,3 ; s x = 0,134  = 5,20 + 0,37 So 95% believe that % mass of Iron is between : 4,83 – 5,57.  = 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

x x xx x X X X X X X X X X X A BCD

X X X X X X X X X X A BCD 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

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