Cara Membuat Larutan-Larutan Penting dalam Percobaan Uji Kandungan Bahan Makanan

Ada beberapa larutan penting yang sangat lumrah dipakai oleh guru-guru di sekolah baik tingkat SMP maupun SMP, untuk mata pelajaran IPA-Biologi atau IPA-Kimia pada percobaan uji bahan makanan. Beberapa larutan yang biasa dipakai itu misalnya: (1) larutan Benedict; (2) Larutan Biuret; (3) Larutan Fehling A dan Fehling B; (4) Larutan Lugol.

Berikut adalah cara-cara untuk membuat larutan-larutan tersebut:
Larutan Benedict
Larutan Benedict digunakan untuk menguji adanya kandungan glukosa dalam suatu bahan (makanan). Adanya glukosa dalam bahan ditandai dengan warna merah bata. Cara membuat larutan Benedict yaitu:
(1) Larutkan 173 gram natrium sitrat dan 100 gram natrium karbonat ke dalam 600 ml air suling.
(2) Panaskan hingga larut, kemudian saring.
(3) Larutkan 17,3 gram kupri sulfat ke dalam 150 ml air suling.
(4) Secara perlahan-lahan, tambahkan larutan kupri sulfat ke dalam larutan natrium sitrat-natrium karbonat. Aduk terus-menerus.
(5) Tambahkan air suling sehingga mencapai volume 1 L.
Larutan Biuret
Larutan Biuret dipakai untuk menguji adanya kandungan protein dalam suatu bahan (makanan).
Cara membuat larutan Biuret yaitu:
(1) Larutan perusi/terusi atau CuSO4 (kupri sulfat) seberat 1 gram ke dalam air suling 99 gram. Wadahilah dalam botol tersendiri.
(2) Larutkan 20 gram NaOH dalam air suling 80 gram. Wadahi dalam botol terpisah.
Cara Penggunaan: Zat yang akan diuji ditetesi dulu dengan larutan NaOH, baru setelah beberapa saat ditetesi dengan larutan perusi. Adanya protein ditandai dengan perubahan warna bahan menjadi ungu.
Larutan Fehling
Cara membuat:
(1) untuk membuat fehling A, larutkan 34,6 gram kristal CuSO4 (kupri sulfat/terusi/perusi) dalam 500 ml air suling. Jika larutan kurang jernih, dapat ditambahkan beberapa tetes asam sulfat pekat.
(2) untuk membuat fehling B, larutkan 77 gram KOH ke dalam 500 ml air suling. Kemudian tambahkan kalium natrium tartrat sebanyak 175 gram, aduk sampai semuanya larut.
(3) Fehling A dan Fehling B disimpan dalam botol terpisah. Keduanya dapat dicampur dengan perbandingan yang sama saat akan digunakan. Larutan Fehling digunakan untuk menguji gula pereduksi.
Larutan Lugol
Larutan Lugol adalah larutan yang sering digunakan untuk menguji adanya kandungan amilum. Cara membuatnya adalah sebagai berikut:
(1) Larutkan 6 gram KI dalam 100 ml air suling.
(2) tambahkan 3 gram kristal iodium, aduk sampai rata.
(3) Saat akan digunakan, larutan tersebut harus diencerkan dengan air suling. Perbandingannya 1:10.

https://suhadinet.wordpress.com/2010/05/23/cara-membuat-larutan-larutan-penting-dalam-percobaan-uji-kandungan-bahan-makanan/

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