Fold and Fault, Caustic Soda and Caustic Potash: Chemistry in Air and Applications

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Fold & Fault

Fold

A fold is a bend in a rock layer caused by forces within the crust of the earth. Folds usually occur in a series and look like waves in the rock.

Fault

Rock layers can also break, in which case a fault occurs. A fault zone is where the sides of broken rock have moved relative to each other.

Caustic Soda and Caustic Potash

Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are both strongly alkaline, corrosive solids. As chemical re-agents, they are mostly interchangeable, although some differences exist in specific applications.

Chemistry in Air

  • Sodium hydroxide, also known as lye or caustic soda, and potassium hydroxide, also known as caustic potash, are both white solids.

  • They are hygroscopic, meaning they will absorb water from the air. Sodium hydroxide will form sodium carbonate ( washing soda) by absorption of carbon dioxide Potassium hydroxide, however, will form potassium bicarbonate 2.

  • Solubility o Sodium and potassium hydroxide are strong bases. At room temperature, they exhibit almost identical solubilities in water - 111 grams of sodium hydroxide will dissolve in 100 milliliters of water vs. 110 grams of potassium hydroxide.

Applications

Both hydroxides can be used in the saponification of fats to form soap. Soaps prepared from potassium hydroxide tend to exhibit greater solubility and are commonly referred to as “soft” soaps.

Manufacture

Sodium and potassium hydroxides are prepared commercially by electrolysis of sodium chloride (NaCl, table salt) or potassium chloride (KCl):

Differences

In many applications, potassium and sodium hydroxide can be freely interchanged. The primary difference between them is cost. In ton quantities, potassium hydroxide is about three times more expensive than sodium hydroxide.

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