燒堿(學名氫氧化鈉)是可溶性的強堿。純堿(學名碳酸鈉)實際上是個鹽，由于它在水中發生水解作用而使溶液呈堿性，再由于它和燒堿有某些相似的性質，所以它與燒堿并列，在工業上叫做“兩堿”。 燒堿和純堿都易溶于水，呈強堿性，都能提供Na+離子。這些性質使它們被廣泛地用于制肥皂、紡織、印染、漂白、造紙、精制石油、冶金及其他化學工業等各部門中。 普通肥皂是高級脂肪酸的鈉鹽，一般是用油脂在略為過量的燒堿作用下進行皂化而制得的。 如果直接用脂肪酸作原料，也可以用純堿來代替燒堿制肥皂。 印染、紡織工業上，也要用大量堿液去除棉紗、羊毛等上面的油脂。生產人造纖維也需要燒堿或純堿。例如(ru)，制粘(zhan)(zhan)膠(jiao)纖維(wei)(wei)首(shou)先(xian)要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)18～20%燒(shao)堿(jian)(jian)(jian)(jian)(jian)溶(rong)(rong)液(ye)(ye)(ye)(或(huo)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)溶(rong)(rong)液(ye)(ye)(ye))去浸(jin)漬(zi)纖維(wei)(wei)素，使它(ta)成(cheng)(cheng)為(wei)(wei)堿(jian)(jian)(jian)(jian)(jian)纖維(wei)(wei)素，然后(hou)(hou)將(jiang)(jiang)堿(jian)(jian)(jian)(jian)(jian)纖維(wei)(wei)素干燥、粉碎(sui)，最后(hou)(hou)用(yong)(yong)(yong)(yong)稀堿(jian)(jian)(jian)(jian)(jian)液(ye)(ye)(ye)把(ba)(ba)磺酸(suan)(suan)(suan)(suan)鹽溶(rong)(rong)解(jie)(jie)，便得到(dao)(dao)粘(zhan)(zhan)膠(jiao)液(ye)(ye)(ye)。再(zai)(zai)經(jing)過濾、抽真(zhen)空(去氣泡)，就(jiu)可用(yong)(yong)(yong)(yong)以(yi)抽絲了。 精(jing)制石(shi)(shi)油(you)(you)也要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)燒(shao)堿(jian)(jian)(jian)(jian)(jian)。為(wei)(wei)了除去石(shi)(shi)油(you)(you)餾分(fen)中(zhong)的(de)(de)(de)(de)膠(jiao)質(zhi)，一般在(zai)石(shi)(shi)油(you)(you)餾分(fen)中(zhong)加濃硫(liu)酸(suan)(suan)(suan)(suan)以(yi)使膠(jiao)質(zhi)成(cheng)(cheng)為(wei)(wei)酸(suan)(suan)(suan)(suan)渣而析出。經(jing)過酸(suan)(suan)(suan)(suan)洗后(hou)(hou)，石(shi)(shi)油(you)(you)里還含(han)有(you)(you)酚(fen)、環烷酸(suan)(suan)(suan)(suan)等(deng)酸(suan)(suan)(suan)(suan)性雜質(zhi)以(yi)及多余的(de)(de)(de)(de)硫(liu)酸(suan)(suan)(suan)(suan)，必須用(yong)(yong)(yong)(yong)燒(shao)堿(jian)(jian)(jian)(jian)(jian)溶(rong)(rong)液(ye)(ye)(ye)洗滌，再(zai)(zai)經(jing)水洗，才能得到(dao)(dao)精(jing)制的(de)(de)(de)(de)石(shi)(shi)油(you)(you)產品。 在(zai)造紙工業中(zhong)，首(shou)先(xian)要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)化(hua)學(xue)(xue)方法處理(li)，將(jiang)(jiang)含(han)有(you)(you)纖維(wei)(wei)素的(de)(de)(de)(de)原料(如(ru)木(mu)材)與(yu)化(hua)學(xue)(xue)藥(yao)(yao)劑蒸煮(zhu)制成(cheng)(cheng)紙漿。所謂(wei)堿(jian)(jian)(jian)(jian)(jian)法制漿就(jiu)是(shi)(shi)用(yong)(yong)(yong)(yong)燒(shao)堿(jian)(jian)(jian)(jian)(jian)或(huo)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)溶(rong)(rong)液(ye)(ye)(ye)作為(wei)(wei)蒸煮(zhu)液(ye)(ye)(ye)來除去原料中(zhong)的(de)(de)(de)(de)木(mu)質(zhi)素、碳(tan)水化(hua)合(he)物和(he)(he)樹脂等(deng)，并中(zhong)和(he)(he)其(qi)中(zhong)的(de)(de)(de)(de)有(you)(you)機(ji)(ji)酸(suan)(suan)(suan)(suan)，這樣就(jiu)把(ba)(ba)纖維(wei)(wei)素分(fen)離出來。 在(zai)冶(ye)金(jin)工業中(zhong)，往(wang)往(wang)要(yao)(yao)(yao)把(ba)(ba)礦(kuang)(kuang)(kuang)石(shi)(shi)中(zhong)的(de)(de)(de)(de)有(you)(you)效(xiao)成(cheng)(cheng)分(fen)轉(zhuan)變成(cheng)(cheng)可溶(rong)(rong)性的(de)(de)(de)(de)鈉(na)(na)(na)鹽，以(yi)便除去其(qi)中(zhong)不溶(rong)(rong)性的(de)(de)(de)(de)雜質(zhi)，因此，常(chang)需(xu)要(yao)(yao)(yao)加入純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)(它(ta)又是(shi)(shi)助(zhu)熔(rong)劑)，有(you)(you)時也用(yong)(yong)(yong)(yong)燒(shao)堿(jian)(jian)(jian)(jian)(jian)。例如(ru)，在(zai)鋁的(de)(de)(de)(de)冶(ye)煉(lian)過程(cheng)中(zhong)，所用(yong)(yong)(yong)(yong)的(de)(de)(de)(de)冰晶石(shi)(shi)的(de)(de)(de)(de)制備和(he)(he)鋁土礦(kuang)(kuang)(kuang)的(de)(de)(de)(de)處理(li)，都要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)到(dao)(dao)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)和(he)(he)燒(shao)堿(jian)(jian)(jian)(jian)(jian)。又如(ru)冶(ye)煉(lian)鎢(wu)時，也是(shi)(shi)首(shou)先(xian)將(jiang)(jiang)精(jing)礦(kuang)(kuang)(kuang)和(he)(he)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)焙燒(shao)成(cheng)(cheng)可溶(rong)(rong)的(de)(de)(de)(de)鎢(wu)酸(suan)(suan)(suan)(suan)鈉(na)(na)(na)后(hou)(hou)，再(zai)(zai)經(jing)酸(suan)(suan)(suan)(suan)析、脫水、還原等(deng)過程(cheng)而制得粉末狀(zhuang)鎢(wu)的(de)(de)(de)(de)。 在(zai)化(hua)學(xue)(xue)工業中(zhong)，制金(jin)屬鈉(na)(na)(na)、電解(jie)(jie)水都要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)燒(shao)堿(jian)(jian)(jian)(jian)(jian)。許多無機(ji)(ji)鹽的(de)(de)(de)(de)生產，特別(bie)是(shi)(shi)制備一些鈉(na)(na)(na)鹽(如(ru)硼砂(sha)、硅酸(suan)(suan)(suan)(suan)鈉(na)(na)(na)、磷酸(suan)(suan)(suan)(suan)鈉(na)(na)(na)、重鉻(ge)酸(suan)(suan)(suan)(suan)鈉(na)(na)(na)、亞硫(liu)酸(suan)(suan)(suan)(suan)鈉(na)(na)(na)等(deng)等(deng))都要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)到(dao)(dao)燒(shao)堿(jian)(jian)(jian)(jian)(jian)或(huo)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)。合(he)成(cheng)(cheng)染料、藥(yao)(yao)物以(yi)及有(you)(you)機(ji)(ji)中(zhong)間體(ti)等(deng)也要(yao)(yao)(yao)用(yong)(yong)(yong)(yong)到(dao)(dao)燒(shao)堿(jian)(jian)(jian)(jian)(jian)或(huo)純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)。 此外，純(chun)(chun)(chun)(chun)堿(jian)(jian)(jian)(jian)(jian)還用(yong)(yong)(yong)(yong)于食品工業和(he)(he)日(ri)常(chang)生活。