Question

I know that metal carbonates decompose to a metal oxide and carbon dioxide upon heating and I was curious if phosphates (eg K3PO4) displayed similar behaviour? Or are they like sulphates where some decompose, such as Iron (II) sulphate, while others such as sodium sulphate do not (this behaviour also confuses me). I realise that unlike carbon and sulphur oxides, phosphorus oxide is not a gas, so will this have an impact? Or will it just not decompose for some reason?

So far my online research hadn't resulted in anything substantial, with searching of 'decomposition of sodium phosphate' resulting in academic papers that are very hard to understand (and don't appear to directly answer my question) and a single result that it will decompose to Na + PO4 (AI generated nonsense, clearly wrong).

Answer 1

Some phosphates, like calcium phosphate, decompose under certain conditions to yield phosphorus oxides and other products, but the stability and decomposition behavior of phosphates are inconsistent and complex, varying widely among different compounds.

Step-by-step explanation:

Just as metal carbonates decompose upon heating to yield metal oxides and carbon dioxide, some phosphates behave in a similar manner under certain conditions. For instance, when calcium phosphate is heated with silicon dioxide and carbon, it decomposes to form calcium silicates, carbon monoxide, and phosphorus, which can then be oxidized to form phosphorus(V) oxide (P4O10). This particular reaction is important in the industrial preparation of phosphorus and its compounds.

In general, heating phosphates might not always lead to a simple decomposition like the formation of a metal oxide and gaseous phosphorus oxides because, as you correctly noted, phosphorus oxides are solid at room temperature and do not readily escape as a gas. Moreover, the stability of phosphates when heated can vary widely depending on the particular compound and the conditions applied. For example, unlike metal carbonates, some sulfates and phosphates decompose at high temperatures, or in the presence of reducing agents, or do not decompose at all, confirming the complexity of predicting the behavior of phosphates upon heating.