碳酸钠，俗名苏打、纯碱、洗涤碱，生活中亦常称“碱”。化学式：Na₂CO₃，普通情况下为白色粉末，为强电解质。密度为2.532g/cm，熔点为850℃，易溶于水，具有盐的通性。

反应分三个步骤进行：

反应生成的二氧化碳（CO₂）可以回收再用，而氯化铵（NH₄Cl）又可以与生石灰反应，产生NH₃，重新作为原料使用：

氨碱法使生产实现了连续性生产，食盐的利用率得到提高，产品质量纯净，因而被称为「纯碱」，但最大的优点还在于成本低廉。

侯氏（联合制碱法）与索氏两法的区别是对于氯化铵的处理。索氏是加入生石灰发使氨逸出，而侯氏是加入食盐使氯化铵结晶而出。

Sodium carbonate (also known as washing soda, soda ash and soda crystals), Na₂CO₃, is the water-soluble sodium salt of carbonic acid.

It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Pure sodium carbonate is a white, odorless powder that is hygroscopic (absorbs moisture from the air). It has a strongly alkaline taste, and forms a moderately basic solution in water. Sodium carbonate is well known domestically for its everyday use as a water softener. It can be extracted from the ashes of many plants growing in sodium-rich soils, such as vegetation from the Middle East, kelp from Scotland and seaweed from Spain. Because the ashes of these sodium-rich plants were noticeably different from ashes of timber (used to create potash), they became known as "soda ash". It is synthetically produced in large quantities from salt (sodium chloride) and limestone by a method known as the Solvay process.