Ian Jackson wrote:

In message , Jeff Layman
writes
On 30/10/19 08:07, Ian Jackson wrote:
In message ,
writes On Wednesday, 30 October 2019 02:44:07 UTC,
Jake wrote: I poured caustic soda down my shower hole and it has
harderned any leads ? I'm panicking water dissolves it. Vinegar
dissolves it faster, but beware of splash
from caustic, a chemical that can blind you.

Some brands of caustic soda 'harden'. With others, there's a rapid,
heat-producing reaction with the water, and dissolve totally without a
trace. Why is this? Have the former been 'cut' - ie something has added
to bulk it out (such as washing soda)?

It's probably due to the amount of water added and the complex hydrates
sodium hydroxide forms with water, particularly the eutectic mixtures
of varying solubility:
https://en.wikipedia.org/wiki/Sodium_hydroxide#Hydrates

"A hot water solution containing 73.1% (mass) of NaOH is an eutectic
that solidifies at about 62.63 °C as an intimate mix of anhydrous and
monohydrate crystals."

Thanks. I'll study that. One thing I didn't mention was that my water is
extremely hard, and it may be the calcium that does it. However, it does
seem that some brands of caustic soda are worse than others.

My guess would be the size and shape of the pellets and the rate of
adding water would be important factors. Aren't you supposed to
gradually add the NaOH to the water and use the solution?


--

Roger Hayter