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Jumat, 09 Desember 2011

Pemeriksaan Kadar Kafein dalam Teh

Praktek Kimia AMAMI
Analisa Kadar Kafein dalam Teh


Tujuan : 
untuk mengetahui kadar kafein dalam teh

Metode : Iodometri

Reagen : 
As.sulfat 10%
alkohol
larutan Iodium 0,100 N 
Indikator amylum  
larutan natrium thiosilfat / Na2S2O3

Cara kerja :

  • Timbang 2,5 gram teh, masukkan dalam beaker glass dan tambahkan air sebanyak 100 mL
  • Didihkan selama 30 meni, kemudian di saring
  • Filtratnyadi kisatkan / usapkan sampai volume ± 20ml, dinginkan titrat dan masukkan kedalam labu ukur 100ml
  • Tambahkan alkohol 25ml, homogenkan ± 10 - 15 menit
  • Tambahkan 5ml asam sulfat 10% dan larutan iodium 0,100 N
  • Homogenkan hingga tercampur dan encerkan sampai batas
  • Pipet 20ml larutan tersebut dan masukkan ke dalam erlenmeyer
  • Tambahkan indikator amylum 1-5 tetes, Titrasi dengan larutan natrium thiosulfat 0,100 N sama warna biru hilang
  • Lakukan pengerjaan secara duplo

Rumus Perhitungan :
 (20 - Vt. Na2S2O3) x 0,00485  x 100 %  = ...... % Kafein
                    Berat Teh

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2 komentar:

  1. Unknown21 April 2012 pukul 23.24

    tolong jelasin perhitungannya.

    BalasHapus
  2. Rizqi Murtafi'ah24 April 2012 pukul 19.11

    Rumus : [ 20 - Vt. Na2S2O3 ] x 0,00485 x 100% / berat teh = ... %kafein

    menurut yang saya dapat ketahui dr pmbelajaran saya waktu prktikum begini ,

    • 20 = larutan teh yg di pipet
    • Vt. Na2S2O3 = Volume Titrasi yg mana titrasi trsebut akan di hentikan pd saat larutan brwarna biru tetap hilang
    • 0,00485 = dalam 1 ml Iodium 0,100N = 0,00485gr kafein
    • Berat teh = berat teh yang di timbang

    Contoh :
    Volume titrasi = 11,7
    Berat teh = 2,5426 gr
    [ 20 - Vt. Na2S2O3 ] x 0,00485 x 100% / berat teh = ... %kafein
    [20 - 11,7 ] x 0,00485 x 100% / 2,5426 = 1,5832 %kafein

    maaf jika masih ada kekurangan, karena saya juga masih belajar :)

    BalasHapus

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