BULETIN KIMIA JAN-08

BULETIN KIMIA

ADA APA DENGAN APEL>>>???

Makan satu apel setiap hari, konon menjadikan tubuh kita sehat, kulit mulus serta bebas dari penyakit kanker... wow...! Siapapun orangnya pasti ingin senantiasa tampil cantik, segar dan sehat sebab kita tahu, tanpa tanpa didukung fisik yang baik maka apapun kegiatan kita akan terhambat.
Ngomong-ngomong masalah apel, buah ini bersama dengan gerombolannya seperti pear, pisang, salak bahkan kentang ketika baru saja dikupas, dipotong atau digigit lalu dibiarkan di udara atau ketika segelas juice apel yang baru saja disodorkan lambat laun berubah menjadi coklat maka selera meneguknya menajdi berkurang. Ada apa ya??? And gak enak dilihatnya ya....

Dalam ilmu pangan, gejala itu dinamai reaksi enzimatis atau browning atau pencoklatan. Yaitu, terbentuknya warna coklat pada bahan pangan secara alami atau karena proses tertentu. Yang pasti bukan akibat zat warna. Pada kelompok makanan tertentu, seperti pada produk bakery (berbagai roti, snack, kacang-kacangan, daging panggang, kopi, teh, dan pada permen coklat) browning umumnya diminati. Sebaliknya, pada kelompok buah-buahan proses pencoklatan itu nampaknya tak dikehendaki. Pencoklatan pada buah apel dan buah lain setelah dikupas disebabkan oleh pengaruh aktivitas enzim Polypenol Oxidase (PPO), yang dengan bantuan oksigen akan mengubah gugus monophenol menjadi O-hidroksi phenol, yang selanjutnya diubah lagi menjadi O-kuinon. Gugus O-kuinon inilah yang membentuk warna coklat.
Untuk mencegah terbentuknya warna coklat pada buah-buah itu, kita dapat melakukannya dengan cara blanching atau pemanasan. Caranya, setelah dikupas dan dipotong-potong, buah apel direndam dalam air panas (suhu 82 - 93 derajat Celcius) atau dikenai uap air panas selama 3 menit. Selanjutnya, direndam dalam larutan jeruk lemon/asam sitrat/vitamin C. Maksudnya, untuk menonaktifkan enzim penyebab pencoklatan itu. Atau dengan mengatur pH misalnya diberi asam atau basa sehingga kerja enzim dihambat maka proses pencoklatan tidak akan terjadi.
Kenapa sih bisa begitu???

Sebagai siswa yang telah mempelajari kimia tentang asam-basa dan pH, ayo terapkan ilmumu untuk menyelesaikan masalah sehari-hari yang ada di sekitarmu. Kerjakan tugas proyek bersama kelompok kerjamu dan buatlah suatu karya ilmiah tentang itu…dalam sumber yang telah kamu catat di kelas…let’s inovate!!!

(ES)

Kesetimbangan larutan: Asam & Basa
The Preface of Acid and Base


Helllo my dearly students….
(read, learn and let’s you discuss with your friends this topic then answer the questions below and send it as your first task in this subject…)

ACIDS AND BASES ARE EVERYWHERE

Every liquid you see will probably be either an acid or a base. The only exception would be distilled water. Distilled water is just water. That's it. Most water you drink has ions in it. Those ions in solution make something acidic or basic. In your body there are small compounds called amino acids. Those are acids. In fruits there is something called citric acid. That's an acid, too. But what about baking soda? When you put that in water, it makes a base. Vinegar? Acid.

Scientists use something called the pH scale to measure how acidic or basic a liquid is. The scale goes from values very close to 0 through 14. Distilled water is 7 (right in the middle). Acids are found between a number very close to 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. They are either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers go to the extremes. If you ever go into a chemistry lab, you could find solutions with a pH of 1 and others with a pH of 14. There are also very stong acids with pH values below one such as battery acid. Bases with pH values near 14 include drain cleaner and sodium hydroxide (NaOH). Those chemicals are very dangerous. NAMES TO KNOW Here are a couple of definitions you should know:Acid: A solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp". Base: A solution that has an excess of OH- ions. Another word for base is alkali.Aqueous: A solution that is mainly water. Think about the word aquarium. AQUA means water. Strong Acid: An acid that has a very low pH (0-4).Strong Base: A base that has a very high pH (10-14). Weak Acid: An acid that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (3-6). Weak Base: A base that only partially ionizes in an aqueous solution. That means not every molecule breaks apart. They usually have a pH close to 7 (8-10). Neutral: A solution that has a pH of 7. It is neither acidic nor basic. WHAT REALLY HAPPENS What really happens in those solutions? It gets a little tricky here. We'll give you the straight answer. Acids are compounds that break into hydrogen (H+) ions and another compound when placed in an aqueous solution. Bases are compounds that break up into hydroxide (OH-) ions and another compound when placed in an aqueous solution. Let's change the wording a bit. If you have an ionic compound and you put it in water, it will break apart into two ions. If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solution is basic. There are other ions that make acidic and basic solutions, but we won't be talking about them here.
That pH scale we talked about is actually a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the pH is very low. If there are a lot of OH- ions, that means the number of H+ ions is very low, so the pH is high.
That's basically it.


Answer these questions and send your answer:

Wha’ts an acid? Give the examples.
What’s a base? Give the examples
What’s pH?
Explain the method to measure how acidic or basic a liquid is.
What are the differences between weak and strong acid and base?
Why the distilled water was classified as a neutral solution and how much its pH?

(EZ)