Video: EC17-18-S1-Q29

Write an experimental process that would allow you to distinguish between silver iodide and silver phosphate.

02:05

Video Transcript

Write an experimental process that would allow you to distinguish between silver iodide and silver phosphate.

What this question is looking for is some kind of experimental test, where we would get one result for silver iodide and another result for silver phosphate. Both silver iodide and silver phosphate are poorly soluble in water. So, dissolving the two solids isn’t going to give a very clear indication of which is which. Silver iodide and silver phosphate are also yellow solids, with melting points that are too high to test for in common laboratory conditions. It would take a furnace to tell the difference between the melting points of these two solids.

However, there is an easy way of telling these two solids apart, using techniques to do with solution analysis. Silver ions, usually in the form of silver nitrate, can be used to test for the presence of iodide ions. The yellow precipitate produced is silver iodide. Silver can also be used to test for the presence of phosphate ions. Again, a yellow precipitate is produced, this time silver phosphate. These precipitates can be distinguished by treating them with ammonia solution. Silver iodide does not dissolve while silver phosphate does.

So how can we use this knowledge to distinguish between two yellow powders? We start by adding ammonia solution to the two solids. Silver iodide is insoluble in ammonia solution and will not dissolve. Silver phosphate is soluble in ammonia solution and will dissolve. So here we have a single experimental process that would allow us to distinguish between silver iodide and silver phosphate.

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