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Nitric acid - addendum


G’day Orchid; I saw the following pieces in Orchid this morning in
response to the general enquiry about nitric acid by ‘Susan’.
Somebody responded:-

....The concentrated acid is an oily liquid that fumes slightly,
especially when there is a lot of water vapour in the air. Never
smell the bottle! .... 

Sorry but I must contradict the first part of that; Concentrated
nitric acid, HNO3 is NOT an oily liquid; it is quite as mobile as
water. It nearly always has a pale yellow colour because the brown
oxide of nitrogen is present in the liquid. Nitric acid is slightly
unstable, and as I said before, it dissociates slowly into the oxides
of nitrogen and oxygen, especially in the presence of light.

As for smelling the bottle, there is a way of doing that safely.
Open a bottle well away from you. Keep the stopper in your hand,
holding the bottle about 10 inches or so away from your face. With
the other hand waft the air above the bottle mouth gently towards
you and sniff very carefully. If you smell nothing, bring the bottle
very slowly towards you, wafting continuously. That way you will
find out safely what the substance in the bottle smells like.

Again, at age 14 I had to clean, dust and re-label where necessary,
every bottle in the Chemistry Department store twice a year. So
now you could say I have a trained nose - and it is just as sensitive
as ever, even now.

To neutralize the dilute acid use any household alkali. Baking
soda, washing soda and lye will all work 

Please don’t use lye - caustic soda - to neutralize acids. It will
do it all right, BUT! The reaction is violent, and caustic soda
itself is a hazardous substance.

Someone else wrote:-

Always add water to the acid, vs the opposite as you can end up a
violent reaction. 

Again I feel I must contradict that remark. Make a habit of always
adding acids and other liquids to be diluted, to water; NEVER add
WATER to ACID The reason for this advice is that if you add water to
acid, you may have a strong reaction at the water / acid interface,
and if the reaction is really strong, considerable heat will be
generated at that layer, steam will form and blow the contents of the
vessel upwards; thus constant stirring is always necessary and the
addition must be done slowly. In the case of concentrated sulphuric
acid, this liquid is heavy and rather oily - indeed it used to be
called “Oil of Vitriol”, and if water is poured into sulphuric acid
the sudden violent generation of heat and steam at the interface is
extremely dangerous. And inevitable. You see, the water, being much
lighter than sulphuric acid will float on the surface of the acid.
An the result is always POUFF-BOUME! as the French sometimes say.
Nasty. – Cheers for now,

John Burgess; @John_Burgess2 of Mapua, Nelson NZ