Thermal Stability of Group 2 Compounds

Question 1

what is thermal stability

Answer 1

the measure of how stable a compound is when heated

Question 2

what would be the extremes of a compounds thermal stability

Answer 2

• not decomposing at all (very stable)

- decomposing as much as possible (very unstable)

Question 3

when you melt a group 1 halide, it is thermally decomposing or not and why

Answer 3

• it isnt
• because you are simply separating the ions from their giant lattice to being in a fluid state
• therefore nothing is decomposed simply due to its change of state

Question 4

when group 2 nitrates or carbonates are heated, do they melt or decompose

Answer 4

they decompose

Question 5

what three factors make group 2 compounds different from group 1 compounds

Answer 5

• charge on group 2 cation is double that of a group 1 cation
• the ionic radius of group 2 cations are smaller than group 1’s (increase in nuclear charge)
• nitrate and carbonate ions are more complex than halide ions

Question 6

why do group 2 nitrates decompose when heated

Answer 6

• because its more complex it can change into smaller and more stable ions
• like NO2- or O^2-
• in which they an decompose and release oxygen or nitrogen dioxide gas

Question 7

why do group 2 carbonates decompose when heated

Answer 7

• its more complex so it can change into a smaller and more stable ion
• like O^2-
• which would decompose and react with the carbon to form CO2

Question 8

how does the difference between the group 1 and 2 charges and atomic radii play a role in the stabilities of the anions

Answer 8

• the stabilities of NO3- and CO3^2- decrease with the increasing charge of the anion
• stability also decreases with the decrease in atomic radius
• so the group 2 cations affect the anions more

Question 9

what observational similarity do all group 1 and 2 nitrates have in common

Answer 9

they are all white solids

Question 10

what products are formed when the nitrates are heated and decompose

Answer 10

• they decompose to nitrites and oxides

- so they give off nitrogen dioxide and oxygen

Question 11

what other product will be formed if the nitrate contains water of crystallisation

Answer 11

steam (H2O)

Question 12

what does nitrogen dioxide look like

Answer 12

brown fumes

Question 13

if no brown fumes are given off, what would be the work equation for the decomposition of a metal nitrate instead

Answer 13

metal nitrate = metal nitrite + oxygen

Question 14

what is the difference between nitrates and nitrites

Answer 14

• nitrate = nitrate(V) or +5

- nitrite = nitrate(III) or +3

Question 15

what would the equation be for the complete decomposition of a metal nitrate

Answer 15

metal nitrate = metal oxide + nitrogen dioxide + oxygen

Question 16

what would the results of heating every group 1 nitrate be with the result being either brown fumes or no fumes

Answer 16

• lithium nitrate would produce brown fumes

- the rest wouldnt

Question 17

what would the results of heating every group 2 nitrate be with the result being either brown fumes or no fumes

Answer 17

all of them would produce brown fumes

Question 18

what would the results of decomposing every group 1 and 2 nitrate therefore be, with the results being either greater or lesser decomposition

Answer 18

• only lithium nitrate in group 1 would go through greater decomposition
• the rest of group 1 would go through lesser
• then all of group 2 would go through greater

Question 19

why is lithium nitrate an exception to the pattern

Answer 19

• the stabilities of the anions decrease if the size of the cation decreases
• lithium is the smallest cation out of all of them
• this is significant enough for it to have greater decomposition

Question 20

what do all group 1 and 2 carbonates look like

Answer 20

white solids

Question 21

why can no observations be made during the decomposition of carbonates

Answer 21

• because the product, CO2, is colourless

- and the carbonate and oxide ions formed are also white

Question 22

what would the results of decomposing every group 1 and 2 carbonate be, with the results being decomposition or no decomposition

Answer 22

• lithium carbonate is the only group 1 carbonate that decomposes
• all of the group 2 carbonates decompose

Question 23

what does lithium carbonate decompose to

Answer 23

• Li = 1+ and CO3 = 2- so Li2CO3

- Li2CO3 = Li2O + CO2

Question 24

what is the general equation for the decomposition of metal carbonates, using M

Answer 24

MCO3 = MO + CO2