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Can you mix HCl and H2SO4 safely?
simenmm:
Hi, non-chemist nanotech PhD student who needs to work with harsh chemicals here. I'm looking to make an etchant containing both HCl and H2SO4. It needs to be quite acidic, currently we are using 20% HCl in our process. However if we were to mix the two directly we'd make a lot of HCl gas, which is not cool in our multiuser environment. Is there a way to make a solution like this safely? There can be other ions present.
chenbeier:
What is the concentration of the sulfuric. Better is to use sodium chloride and sulfuric acid, because the HCl will produced then. Conc. sulfuric adsorbs a lot off water and evaporate HCl gas, not a good idea.
phth:
--- Quote from: simenmm on March 11, 2019, 09:26:12 AM ---Hi, non-chemist nanotech PhD student who needs to work with harsh chemicals here. I'm looking to make an etchant containing both HCl and H2SO4. It needs to be quite acidic, currently we are using 20% HCl in our process. However if we were to mix the two directly we'd make a lot of HCl gas, which is not cool in our multiuser environment. Is there a way to make a solution like this safely? There can be other ions present.
--- End quote ---
Mix before use? It seems simpler if you have a problem of a premixed solution fuming while use to switch the acid to a less volatile one.
Borek:
--- Quote from: chenbeier on March 11, 2019, 04:39:27 PM ---Better is to use sodium chloride and sulfuric acid, because the HCl will produced then.
--- End quote ---
I don't see how it it is better. It is exactly as dangerous, if not worse. As there is less total water, chances that HCl will get airborne are much higher.
simenmm:
--- Quote from: chenbeier on March 11, 2019, 04:39:27 PM ---What is the concentration of the sulfuric. Better is to use sodium chloride and sulfuric acid, because the HCl will produced then. Conc. sulfuric adsorbs a lot off water and evaporate HCl gas, not a good idea.
--- End quote ---
The sulfuric acid is 99% and the HCl is 32%. I don't know what final concentration is necessary because this is a novel process. I've seen youtube videos where people pour H2SO4 onto solid NaCl and it produces a lot of HCl gas, so I'm worried about that.
--- Quote from: phth on March 12, 2019, 01:48:08 AM ---Mix before use? It seems simpler if you have a problem of a premixed solution fuming while use to switch the acid to a less volatile one.
--- End quote ---
Sure, I need it to cool to room temperature before use anyway. But I still need to make the solution in a safe way.
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