|MadSci Network: Chemistry|
Hello Sanne and Linda – there is no single answer to your questions – like so many things – it depends… Let’s tackle your first question – “can you throw acid neutralised away without causing any damage?” first. Acids are neutralised by bases. You could equally well have asked - can you throw base neutralised away without causing any damage? The answer depends on several things – like what do you mean by “throw away”? Down the drain? Secondly the answer will depend on what it is that you are throwing away – neutrality in pH (acidity/alkalinity) is only one parameter to consider. Any neutralisation produces a solution of salts or a precipitate/suspension of insoluble salts of the reaction between acid and base. As extreme examples – you wouldn’t throw sodium cyanide solution down the drain – which fits the description “acid neutralised” whereas sodium chloride (common salt) wouldn’t be a problem – with reasonable dilution and in reasonably small quantity. (Water softeners chuck this down the drain from households all the time.) Then – again assuming you are talking “down the drain” – it depends what kind of drain – and where it leads to – into a septic tank, into a sewer to a sewage works (domestic or industrial) or into a lake, a stream or the sea. Damage will depend on the answer to this as well as what it is and how much and how dilute…. You second question – “is it true that acid and base solutions can be thrown away in the environment because they neutralise each other and there is no heat development and large salt concentrations?” is perhaps easier to answer – the answer is no. Some neutralisations cause lots of heat -–and in any case neutralisation takes some time and mixing before it is complete. It also requires exact equivalence of acid and base to achieve neutrality. So you risk damage before neutralisation by either acid or base, and damage through not achieving neutrality. Also how much salt is formed depends on how much acid and base is involved. The main conclusion on all of this – never put anything down the drain (or into the environment generally) without checking with someone who knows! Your chemistry teacher should be able to tell you. You could even ask the question of the Dutch Department of the Environment. I bet you can find them on the web. Let me know if you get any different answers or if you want to ask me more – my e-mail is email@example.com
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