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Name: Tina
Status: student
Grade: 4-5
Location: OH
Country: USA
Date: Winter 2009-2010

How was lye safely stored before plastic was invented? Why can you not store lye in a glass container?

Lye - which is usually Caustic Soda or Sodium Hydroxide, is traditionally stored in glass. It will after long storage discolour and etch the surface of the glass - but it takes years, and leaves the bottle looking cloudy and perhaps a bit unsightly.

The material that cannot be stored in glass is is Hydrofluoric Acid - HF

Hydrofluoric acid is used to etch glass - like the ones you used to see in fancy barber shops. Now it is sold in plastic containers - High Density Polyethylene. In the past the only safe container was a wax lined ceramic jar. If you watched the first couple of episodes of Breaking Bad they try to use HF to dissolve a body - but rather than find a plastic tub, one of the crooks does the job in the bathtub. Baths are made of metal and the shiny white coating is enamel glass. Guess what happened to the bath??

Nigel Skelton
Tennant Creek High School

There are three terms, used in common language: The first, is "lye". This refers to the chemical compound calcium oxide (CaO). This compound reacts rapidly with water forming (Ca(OH)2) referred to in the older chemical literature as "slaked lime". In the presence of air and or some other source of CO2 forms Ca(CO3), calcium carbonate. You cannot store "lye" in glass because glass (SiO2) can dissolve in highly alkaline solution. The reaction is slow, depending upon particle size, and other variables, but it happens. That is why lye is not stored in glass containers. Before "plastics", which have various resistance to alkaline substances, high purity "lye" was stored in platinum or gold containers. At a less demanding container CaO can be stored in glass if the sample and container are "flame" dried to drive off the water under vacuum.

Vince Calder

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