Telling apart hydrochloric acid and sulphuric acid

[bookend]

I've got two small unlabelled amber reagent bottles containing concentrated (pure) acids.

I know one bottle contains hydrochloric acid and the other contains sulphuric acid. Is there a simple test method by which I can distinguish the acids?

Thank you.

[newtron]

If you have son AgNO3 lying around (I'm asuming you are in a lab since you have these concentrated acids available), you could test for the presence of Cl. Add some of the unknown acid to DI water and then add AgNO3. If a white solid precipitates (AgCl), there is Cl present and you have HCl.

Someone else will probably have a better suggestion.

[shammydodger]

No arguments with that suggestion, Newtron. Precipitation is one of the simplest methods of distinguising between unknowns.

Mind you, the person in charge of the budget might be a little annoyed if you are a touch shaky with the silver nitrate bottle, so use sparingly!

[theprof]

Lab or no lab, let's make it even simpler.

Find yourself a bottle of "strong" ammonia solution if your not in a lab or concentrated ammonium hydroxide solution if you are in a lab.

Carefully place a small quantity of the solution in a shot-glass or similar, or better still, a test-tube or small beaker. Remove the stopper of each reagent bottle in turn and place the mouth of the glass/test-tube/beaker near the top of the bottle so that the vapour from the ammonia reacts with any vapour from the bottle.

You will see a white fog of ammonium chloride forming around the top of the bottle containing the hydrochloric acid.

Well ventilate the area afterwards and ensure all the glassware or other stuff you've used is cleaned thoroughly.

Whilst this method does not comply with modern inorganic qualitative analysis techniques, it is simple and will enable you to distinguish the two acids, which is all you are after. If we knew for certain you were in a lab, I'd be only to pleased to suggest the AgNO3 test and others.

You may also be able to see hydrogen chloride vapour resembling wisps of steam emerging from the open hydrochloric acid bottle when viewed at a distance at eye-level (Caution: hydrogen chloride is toxic as well as being corrosive to mucous membranes) although sometimes, the vapour is hard to see for various reasons.

[bookend]

Thanks all for your answers.

theprof, I've been gobsmacked by your answer. You must have read my mind. You were right not to assume that I had aceess to a lab. I don't and the acids are at home with me. The acids were given to me some years back by an old chemist who was clearing his stuff out after a fire (arson) in his lab.

I bought a bottle of strong ammonia at my local hardware shop this morning and followed your instructions. I soon saw the white cloud at the top of the hydrochloric acid bottle but nothing was seen when the ammonia container was put near the mouth of the sulphuric acid bottle.

Who needs silver nitrate and and other lab stuff when good old ammonia has done the business. Precipitation may well be simple method of distinguishing between unknowns, but you've suggested something simpler still as I didn't even have to get the acids out of their bottles. Besides, I wouldn't have a clue where to buy the silver nitrate anyway.

I've now labeled the acids are put them away safely.

Cheers and thanks again.

[alphamale]

If you don't know what they are (not labelled) then you probably don't need them.

I would carfully dilute them (one at a time) into a large, nearly full bucket of cold water. I would tip this down the drain.

I assume you must have some thing like about 500ml of each. Conc HCl is approx 12 molar, if you can dilute it to, say, 10 litres. If I have calculated it right it should be about 0.6 molar. Tip this down a drain with a couple of large buckets of water after it.

Do the same with the H2S04.

Wear rubber gloves and safety specs to handle the acids. Work outside for ventillation.

If you don't need the acids, get rid of them, but don't dump them. Do it yourself or get your local authority to collect and dispose. Just imagine what would happen if a child got to drink either of these by mistake.

Ace

[Parsley Dump]

Bookend
If the sulphuric acid is concentrated it will react quite violently when it comes into contact with water, you cannot just pour acids down the drain.

[bookend]

I'm no expert on chemistry Parsley Dump, but I can't fault you there.

As far as I remember, adding concentrated sulphuric acid to water generates a hell of a lot of heat. If the bucket was made of plastic (what else nowadays?) there's a serious risk of the bucket melting. It doesn't sound a good idea to me.

I don't understand why alphamale says one minute to pour the dilute acids down the drain and the next minute suggests that I get the local authority to pick the stuff up. How would I "get rid of them" myself if I can't "dump" them?
I'm puzzled.

I've also had a look at the water regulations in my area. Seems that its illegal to pour acids down drains dilute or not. You're right on that too.

[alphamale]

I gave my original advice in good faith. I can see that I was wrong to do so.

I do not believe that you have any idea what you are dealing with. You certainly don't give me the confidence that you are able to handle conc acids safely as you don't know the chemistry of them.

I would strongly suggest that if you believe these to be concentrated acids (and any other waste chemicals) that you should get your local authority to collect them for expert disposal.

If you suspect that you may have HF acid in a plastic bottle again get the proper authority to deal with this as it is highly toxic.

I advise again - if you don't know what they are then you probably don't need them. Dispose of them in a safe and sensible way through your local authority.

Don't store the sulphuric acid with combustible materials such as organic chemicals, card, paper, rags or wood as this is a fire risk.

Go on the web and find the MSDS (from reputable chemical companies) for the acids and any other chemicals that you have to check how they should be stored, their toxicity, fire fighting, adverse reactions etc.