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You may have seen the effect of heat on sodium nitrate. A thermal decomposition reaction took place in which sodium nitrite and oxygen gas were produced: |
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NaNO3(l) ⇒ NaNO2(l) + ½O2(g) |
This is typical of the group 1 metal nitrates, which are relatively stable to heat. However, lithium nitrate decomposes more easily, producing brown nitrogen dioxide gas, oxygen and lithium oxide. We often find that the element at the top of the group behaves differently to the rest. The same type of decomposition was seen with copper(II) nitrate. It is also found on heating group 2 metal nitrates.
Watch the following video in which there is no commentary. A glowing splint is used to test for oxygen in each case. Make notes of the changes you observe for each Group 2 nitrate which is heated. This is good practice for the observation work required in some practical assessments. What do your observations suggest about the trend in thermal stability of these nitrates as we go down the group? Try to explain the trend that you discover - it must have something to do with the different metal ions involved. Write down equations for each of the reactions seen. Check your observations and answers using the theory link below.
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You will find that the magnesium nitrate and calcium nitrate have water of crystallization, whereas the strontium nitrate and barium nitrate are anhydrous. This means that there are different patterns of decomposition and we cannot effectively use the time of decomposition as a measure of stability as we do with the carbonate decompositions. |
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Video - the effect of heat on the group 2 metal nitrates
Theory - the thermal stability of the group 2 metal nitrates
