純氫氧化鈉

哥士的（caustic soda）其實是氫氧化鈉的俗名，兩個名稱指同一樣物質。純的哥士的就是純的氫氧化鈉，不純的哥士的就是不純的氫氧化鈉。

在絕大多數的五金舖都有哥士的出售，這個最方便，而化工原料舖也有哥士的出售。當然售賣給中學及大學的化學品公司（儀器公司），會售賣純度較高的哥士的（氫氧化鈉），但價錢昻貴很多倍。若果你只想做手工皂，對哥士的純度的要求並不高，在五金舖買到的哥士的純度已超過要求了。最大的問題是你下班的時間，差不多所有的五金舖（和化工原料舖）已收舖。你可以托人去五金舖買，亦可以放假時去買，不過有很多五金舖都是星期日休息的。

無純NaOH.......因為純NaOH會係空氣中吸水同酸性氣體(CO2,NO2...)

let me give you the basic information of it to you first,then,i am going to tell you where you can buy it.
ok,first of all,Sodium hydroxide (NaOH), also known as lye, caustic soda and (incorrectly, according to IUPAC nomenclature)[1] sodium hydrate, is a caustic metallic base. Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water.
Pure sodium hydroxide is a white solid; available in pellets, flakes, granules and as a 50% saturated solution. It is deliquescent and readily absorbs carbon dioxide from the air, so it should be stored in an airtight container. It is very soluble in water with liberation of heat. It also dissolves in ethanol and methanol, though it exhibits lower solubility in these solvents than potassium hydroxide. It is insoluble in ether and other non-polar solvents. A sodium hydroxide solution will leave a yellow stain on fabric and paper.


In general such neutralization reactions are represented by one simple net ionic equation:

OH−(aq) + H3O+(aq) → 2H2O
This type of reaction with a strong acid, releases heat, and hence is referred to as exothermic. Such acid-base reactions can also be used for titrations, which is a common method to determine the concentration of acids. Another type of reaction that sodium hydroxide is involved in is with acidic oxides. The reaction of carbon dioxide has already been mentioned, but other acidic oxides such as sulfur dioxide (SO2) also react completely. Such reactions are often used to "scrub" harmful acidic gases (like SO2 and H2S) and prevent their release into the atmosphere.

2NaOH + CO2 → Na2CO3 + H2O

you can buy them in some shops in yeung long,there are plenty of shops you can find.
hope this can help you

2008-11-06 13:02:09 補充：
Paint stripper
A solution of sodium hydroxide in water was traditionally used as the most common paint stripper on wooden objects. Due to its caustic nature and the fact that it can damage the wood surface raising the grain and staining the color, its use has become less common

2008-11-06 13:02:59 補充：
When a penny is boiled in a solution of NaOH together with some granular zinc metal (galvanized nails are one source), the color of the penny will turn silver in about 45 seconds. The reason this happens is that granular zinc dissolves in NaOH to form Zn(OH)42(tetrahydroxozincate). .

2008-11-06 13:03:08 補充：
Alumina production - Bayer process
Sodium hydroxide is used in the refining of alumina containing ore (bauxite) to produce alumina (aluminium oxide) which is the raw material used to produce aluminium metal via the smelting process.

2008-11-06 13:03:22 補充：
Soap production
Sodium hydroxide was traditionally used in soap making (cold process soap, saponification). The Persians & Arabs began producing soap in this way in the 7th century, and the same basic process is used today.

2008-11-06 13:04:49 補充：
Paint stripper


Gold pennies experiment



Aluminium etching
.


Food preparation



Domestic uses



Illegal drugs



Cleansing agent

哥士的是英文(Caustic Soda)的中文音譯。正式名稱是氫氧化鈉 (Sodium Hydroxide)﹐有腐蝕性﹐屬強鹼性。
從前曾Sir經常在香港電視上介紹﹐哥士的可以用來通坑渠﹑去污漬﹑除垢﹑造肥皂﹐哥士的是非常有力的清潔工具﹐因為腐蝕性強和價錢平﹐容易買到。
哥士的已經夠勁﹐如果加埋雙氧水後﹐組成夢幻組合﹐真是無堅不摧﹐化腐朽為神奇。
各位在未食素之前可能都會記得﹐街邊推車仔的豬皮蘿蔔﹑咖喱魷魚﹑街市一盤盤發起的海參﹐酒樓的白雲鳳爪等。他們的鬆軟程度與哥士的大有關係。舉例來說乾魷魚是非常堅韌的﹐尤其是菲律賓出產那一種﹐堅韌度可比美我們的拖鞋﹐浸極水都脹不了多少。劣質紅紅綠綠發霉的乾魷魚﹐加進哥士的浸泡一天之後﹐便會發脹幾倍。因為哥士的腐蝕性強﹐將頑強的組織破壞﹐這樣水分吸收便可通行無阻。如果顏色不好﹐再加雙氧水漂一漂﹐便會非常美觀。
因為哥士的有腐蝕性﹐一般食品製造者（山寨工場）都會長啤水,即使水喉不關﹐一路沖水﹐盡量沖洗餘下的化學物品。但已滲入內部的哥士的﹐就很難說了。所以對人體是有害的。
雖然有上述的另類用途﹐哥士的在正式食品工業上﹐主要用途是用來中和酸性。比如在製造水解植物蛋白時﹐脫脂植物蛋白放進高純食用鹽酸（HCL）的溶液分解﹐將蛋白質（Protein）分解為氨基酸（Amino Acid）,溶液會帶酸性﹐這樣便需要加進鹼性的哥士的（碳酸氫鈉）或碳酸鈉來中和。

氫氧化鈉（NaOH，俗稱燒鹼、火鹼、苛性鈉，在香港稱為哥士的）常溫下是一種白色晶體，具有強腐蝕性。易溶於水，其水溶液呈強鹼性，能使酚酞變紅。
氫氧化鈉是一種極常用的鹼，是化學實驗室的必備藥品之一。它的溶液可以用作洗滌液。
純氫氧化鈉