Ferric chloride anhydrous vs hexahydrate

[shetc]

Hey Guys,

I want to etch some copper. I bought some ferric chloride anhydrous, thinking that I would rehydrate it as and when I needed it. However, when I searched for info on how to mix it up, I couldn't find much on the Internet. Then I came across an article saying I should have bought hexahydrate to do etching, not anhydrous. Any chemists out there know what is the correct type for etching?

Thanks,

Steve

 

[bruce_the_loon]

Hexahydrate is just hydrated anhydrous and the hydrating process is just adding water, so you can use what you bought. Be careful when mixing ferric chloride and water, add the ferric chloride to the water slowly in small amounts and wear gloves.

 

[shetc]

Thanks, Bruce! Can you recommend the ratio of ferric chloride to water? I'm etching some standard copper pipe I bought from Lowes.

 

[bruce_the_loon]

Anything between 10% and 30% by weight, the more concentrated, the faster the etching. On printed circuit boards, the copper is a thin layer that can be undercut by too strong a solution, but pipe is solid copper and it won't eat copper that fast to dissolve through a 1mm copper pipe wall.

I've used it to etch printed circuit boards that have the tracks marked out by using a spray-on etch resist that is light sensitive. You spray it on, then use a clear plastic sheet with the tracks printed on it to develop the spray so it allows etching where you want it.

On copper pipe, you can probably get away with using a Q-tip dipped in it as a pen to etch where you want it, or you can also mask using electrical tape if you've got the patience to cut out the patterns.

 

[shetc]

Hexahydrate is just hydrated anhydrous and the hydrating process is just adding water, so you can use what you bought. Be careful when mixing ferric chloride and water, add the ferric chloride to the water slowly in small amounts and wear gloves.

Thanks, Bruce! Can you recommend the ratio of ferric chloride to water? I'm etching some standard copper pipe I bought from Lowes

 

[IslandLizard]

(Anhydrous) Ferric Chloride is FeCl3.
The hexahydrate is FeCl3 x 6H2O, it includes 6 molecules of water, making up a significant portion of its mass (weight).

162.2 g/mol (anhydrous)
270.3 g/mol (hexahydrate)

Conversion when weighing out anhydrous is 162.2/270.3 = 0.6 the mass of hexahydrate. IOW, the anhydrous form is 67% stronger.

 

[indica]

(Anhydrous) Ferric Chloride is FeCl3.
The hexahydrate is FeCl3 x 6H2O, it includes 6 molecules of water, making up a significant portion of its mass (weight).

162.2 g/mol (anhydrous)
270.3 g/mol (hexahydrate)

Conversion when weighing out anhydrous is 162.2/270.3 = 0.6 the mass of hexahydrate. IOW, the anhydrous form is 67% stronger.

i want to prepare hexahydrate from anhydrous ferric chloride. can yousuggest exact methodology to be followed. thankyou.

 

[IslandLizard]

i want to prepare hexahydrate from anhydrous ferric chloride. can yousuggest exact methodology to be followed. thankyou.

What do you need the hexahydrate for?
Mind, this is a homebrew forum, to make beer, wine, meads, etc. at home.