When you mix unknown solution with potassium carbonate, you should observe a white precipitate forming. This is due to the precipitation of strontium carbonate or magnesium carbonate (depending on which nitrate the unknown solution is). The shape of the precipitate will be determined by the size and shape of the container in which the reaction occurs.
If you want to be sure about which nitrate your unknown solution is, you should also mix it with potassium sulfate. If you observe a white precipitate forming again, then it indicates that your unknown solution contains strontium nitrate. If no precipitate forms, it means your unknown solution contains magnesium nitrate.
It's important to label your chemicals correctly so that you avoid making mistakes like this in the future. Good laboratory practices dictate that all chemicals should be properly labeledand stored appropriately to ensure safety and accuracy in experimental results.