 Why are ammonium salts important? Well, if you've eaten anything before studying today, whether it was fruit, vegetables, bread, or something more processed, at least some of the crops that were grown to make your food, or perhaps feed the animals that went into your food, were almost certainly fertilized using an ammonium salt. To understand something, we need to know how it's created, so let's start there. You might have already guessed that making an ammonium salt starts with ammonia NH3. Ammonia is a base. A weak base, yes, but a base nonetheless. So here's the first question. Can you remember what a base reacts with to produce a salt? And so suggest what we do to ammonia in liquid form to make an ammonium salt. Pause the video and have a think. Well, if you worked out that we react ammonia with an acid to produce the salt, you're absolutely right. Let's look at the reaction with the common acid hydrochloric acid. Being a strong acid, this dissociates in solution to form H plus and Cl minus ions. And what's another name for H plus ion? That's right, a proton. The ammonia molecule can accept a proton. That's what makes it a Lewis base. And we now get an ammonium ion with four hydrogens and a plus one charge. Now here's another question. What is this new ammonium ion going to be attracted to that's present in the solution? Pause again and think. The answer is the chloride ion, which has a minus one charge. Now, remember your ionic bonding. What are the ratios going to be for the ammonium chloride salt that is created? It's one to one. The plus one charge of the ammonium is cancelled out by the minus one of the chloride, meaning ammonium chloride has this formula, NH4Cl. Here's the reaction. Ammonium chloride is an important salt because it's a main component in zinc carbon batteries. Now, here's your main challenge. Let's think about three other popular ammonium salts. Ammonium carbonate is an ingredient of smelling salts, which are not used much these days. But in the past, people used to inhale their vapours when they felt faint. Ammonium nitrate is an important fertilizer. And ammonium phosphate is not only a fertilizer, but can be used to flame-proof wood and clothes. So, here are the carbonate, nitrate and phosphate anions. Can you write the chemical formula of the matching ammonium salt? Pause the video while you write down your answers and resume when finished. The carbonate ion has a two minus charge, so to balance this, we need two ammoniums. The nitrate is minus one, so here we have another one to one ratio. And the phosphate is three minus, so three ammoniums are needed. Pay attention to the use of brackets here. How did you do? As well as being a fertilizer, ammonium nitrate is also used to make explosives. But it's fair to say you won't be doing this in the lab until you become a very experienced chemist. All of these salts are formed in a similar way to that we've already talked about by reacting liquid ammonia with the acid in question. Here's a final little challenge. See if you can balance the final equation. Pause and continue when ready. Here's the answer. How did you do? You might have learnt that an acid plus a base gives a salt and water, and that's quite right most of the time. But interestingly, as you can see, these reactions do not yield water, although it will still be present as a solvent. All of the atoms that make up the reactants come together to form just the one product, the ammonium salt. Speaking of water, all of these simple ammonium salts are highly soluble in it and form solutions. So to get solid salt crystals, we'd have to evaporate the water. The exception to this is this complex-looking salt called ammonium hexachloroplatinate. Don't try saying that with your mouth full. It's used for coating objects with precious platinum metal.