Thermal stability of nitrates and carbonates
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Summary
Thermal stability of nitrates and carbonates
In a nutshell
The thermal stability of nitrates and carbonates increases as you go down Groups and . Thermal stability can be tested by producing gases and testing for them, is tested for nitrates and is produced from carbonates.
Thermal stability of nitrates and carbonates
Thermal stability is based on how much heat a substance can withstand before undergoing thermal decomposition. The higher the thermal stability the higher the temperature required to decompose the compound.
Thermal stability down a group
Thermal stability increases as you go down a group. Carbonates and nitrates are large negative ions (anions). They can be made unstable by the positive ions (cations). The greater the distortion the more this destabilises the anion.
The greater the charge on the cation the more this can destabilise the anion. As well as this the smaller the cation, the higher the charge density and the more this can distort the anion. Going down the group would mean a lower charge density and more thermal stability.
Group 2 are less thermally stable than Group 1
A higher charge density makes the anion more unstable. Group metals have a charge compared to a charge for Group metals which will cause more significant destabilisation. Group carbonates and nitrates are less thermally stable than Group .
Testing for thermal stability
Nitrate decomposition can be measured by...
How long it takes until a glowing split can be relit or how much brown gas is produced. This must be done in a fume cupboard because is toxic.
Example
Decomposition of Group and Group nitrates.
Metals such as potassium and sodium, combust to form nitrite salts. Metals such as; calcium, magnesium, aluminium, zinc, iron, lead and copper decompose to form a metal oxide and release and gas.
Carbonate decomposition can be measured by...
Carbon dioxide is produced when carbonates are decomposed. This can be measured by testing with lime water (saturated solution). A positive result is that the solution turns cloudy.
Example
Decomposition of Group and Group carbonates.
FAQs - Frequently Asked Questions
What is an important factor in the thermal stability of an anion?
A lower charge density for a metal cation would increase the thermal stability of an anion.
How can you test for the decomposition of nitrates?
Metal nitrates thermally decompose and form nitrogen dioxide gas. This can be tested for by seeing how long it takes for a glowing splint to be relit.
How can you test for metal carbonates?
Thermal decomposition of metal carbonates produces carbon dioxide. Carbon dioxide can be bubbled through limewater (saturated NaOH solution) and this will turn the solution cloudy.