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GRAVIMETRI PENGUAPAN
• Analit dipisahkan dari sampel sebagai gas (zat volatil) yang diketahui komposisinya
• Pengukuran massa– Produk volatil yang dijebak– Residu
• Ex. Termogravimetri analisis massa sampel diukur secara kontinyu dengan kenaikan T
Chemistry 215 Copyright D Sharma
3http://radchem.nevada.edu/chem455/lecture_22__thermal_methods.htm
TGA Instrumentation1. A sample (0.1 to 15 mg) is
placed into a tared TGA sample pan, which is attached to a sensitive microbalance.
2. The sample holder (connected to the balance) is subsequently placed into a high temperature furnace.
3. Balance assembly measures the initial sample weight at room temperature and continuously monitors changes in sample weight (losses or gains) as heat is applied to the sample (up to 1500 °C).
Chemistry 215 Copyright D Sharma
4
Thermal Gravimetric Analysis (TGA)
• Precisely monitoring weight loss of a sample in a given atmosphere as a function of temperature and/or time
• Temperature: ambient to 1000 °C• Records the first derivative of the
mass loss
Chemistry 215 Copyright D Sharma
5
TGA cont. • Evaluate the thermal decomposition and stability of
materials– Polymers, resins, rubbers, explosives
• Information on bulk composition of compounds– Thermal oxidation, heat resistance– Residual water or solvents – Compositional analysis – Ash content in a sample– Quantity of inorganic filler in a polymer
Chemistry 215 Copyright D Sharma
6
• The percent weight loss of a test sample is recorded while the sample is being heated at a uniform rate in an appropriate environment.
• The loss in weight over specific temperature ranges provides an indication of the composition of the sample, including volatiles and inert filler, as well as indications of thermal stability.
• The gas environment is pre-selected for either a thermal decomposition (inert – He or N2 gas), an oxidative decomposition (air or O2), or a combination therein.
TGA cont.
Chemistry 215 Copyright D Sharma
8
TGA tests may be run in a heating mode at some controlled heating rate, or isothermally. Typical weight loss profiles are analyzed for the amount or percent of weight loss at any given temperature, the amount or percent of noncombusted residue at some final temperature, and the temperatures of various sample degradation processes.
TGA cont.
Contoh Soal• Dalam termogram penguapan kaslium oksalat monohidrat (146,11
g/mol) dengan berat awal 24,60 mg dipanaskan dari suhu ruang – 1000oC dengan 5o/menit. Perubahan massa sbb– Suhu 100 – 250oC= 3,03 mg
– Suhu 400 – 500oC = 4,72 mg
– Suhu 700 – 850oC =7,41 mg
• Penyelesaian
OHmolgmolgx
xmg
mg
2/00,18/11,146%32,12
%32,12%10060,24
03,3
COmolgmolgx
xmg
mg
/04,28/11,146%19,19
%19,19%10060,24
72,4
2/01,44/11,146%12,30
%12,30%10060,24
41,7
COmolgmolgx
xmg
mg
Penentuan Silika (SiO2) dalam bijih/aliase
• Prinsip dasar– Si SiO2
– SiO2 + 4HF SiF4 + 2 H2O
• Massa SiO2 = massa awal – massa akhir
contoh• A sample slag from blast furnace is analyzed for SiO2 by decomposing
0,5003 g sample with HCl, leaving a residue with a mass of 0,1414 g. after treating with HF and H2SO4 and evaporating volatil SiF4, residue with a mass of 0,0813 g remains.
• Determine %w/w SiO2 dalam sample?
Solution
g 0,1231
g 0,0183 - g 0,1414 SiO 2
massa
%61,24%1005003,0
1231,0% 2 x
g
gSiO
Analisis AnorganikMetode Langsung• Penentuan kadar abu (ash content) dalam polimer• Metode:
Sampel ditimbangcrusdibakarpengabuan
• Penentuan padatan terlarut (TDS)• Metode:
Sampel air crus residu 1 residu 2
%100sampelberat
abuberat abu kadar % x
mLxmLgTDS 100sampel volume
residuberat )100/(
%1001residu
2residu - 1residu content) (organic lzat volati% x
Metode tak langsung• Penentuan kadar air dalam produk
Metode:
Sampel (x gram) residu (y gram)
• Penetuan silika dalam air, bijih, slag, aliase• Penentuan karbon dalam baja
Prinsip dasar: C CO2
%100x
y -x moisture% x
contoh• 101,3 mg sampel senyawa organik diketahui mengandung Cl
dianalisis dengan pembakaran. Gas-gas hasil pembakaran ditampung dalam penyerap. Tabung penyerap CO2 bertambah massanya 167,6 mg, tabung penyerap H2O bertambah massanya 13,7 mg. sampel kedua sebanyak 121,8 mg ditambah HNO3 menghasilkan Cl2 yang kemudian bereaksi dengan AgNO3 membentuk AgCl sebanyak 262,7 mg AgCl. Tentukan persentase unsur-unsur dan rumus empiris!
• Penyelesaian• Sampel 1=101, 3 mg
mgmgx 71,456,167mg/mmol 44
mg/mmol 12 C massa
%12,45%1003,101
mg 45,71 C % x
mg
mmolmmolmg
mol 809,3/12
mg 45,71 C
mgmgx 52,17,13mg/mmol 18
1mg/mmol x 2 H massa
mmolmmolmg
mol 52,1/1
mg 1,52 H
%50,1%1003,101
mg 1,52 H % x
mg
Cont.• Sampel 2 = 121,8 mg
• Penentuan rumus empiris perbandingan molMol C : mol H: mol Cl3,809 : 1,52 : 1,8335 : 2 : 2
Jadi rumus empiris senyawa organik tersebut= C5H2Cl2
%21,53%100mg 8,121
mg/mmol32,143mol35,453mg/m
x mg 262 Cl% x
mgmgx 98,647,262mg/mmol 143,32
mg/mmol 35,453 Cl massa
mmol833,1mg/mmol453,35
mg 64,98 Cl mol
Gravimetri Partikulat
• Pemisahan analit dari matriknya
• Metode– Filtrasi: partikel padat dipisahkan dari matriks
cair, gas, padat– Ekstraksi: cair-cair, cair-padat
Classical extraction method is: SOXHLET EXTRACTION
(named after developer). Apparatus
Sample in porous thimble. Exhaustive reflux for up to 1 - 2 days. Solution of analyte(s) in volatile solvent (e.g. CH2Cl2, CHCl3 etc.) Evaporate to dryness or suitable concentration, for separation/analysis.
Contoh soal
• 200 mL sampel air disaring dengan penyaring serat kaca, setelah dikeringkan pada 105oC dan berat konstan, maka berat penyaring bertambah sebesar 48,2 mg. tentukan total suspended solid dalam ppm (mg/L)
• Penyelesaian
ppmLmgL
mgppmTSS 241/241
200,0
2,48)(
Penentuan NH3 dalam Garam Amonium
• Larutan garam amonium + NaOH berlebih dan dipanaskan. Gas NH3 dialirkan ke dalam larutan asam standar berlebih, kelebihan asam dititrasi dengan larutan standar basa
• NH4+ + OH- NH3 + H2O
• NH3 + H+ NH4+
• H+ sisa + OH- H2O