group 1 + 2 compounds

Question 1

thermal decompisition

Answer 1

• substance breaks down when heated

- the more thermally stable it is the more heat it’ll take to break it down

Question 2

thermal stability increases down the group

Answer 2

• carbonate and nitrate ions are large negative ions and can be made unstable by presence of positively charged ion
• cation polarises anion distorting it which means there’s a greater distortion so the compound is less stable
• large cations cause less distortion than small which means lower charge density so the charge on ion is spread out over a large area
• so this means as you go down the cations get larger so the charge density gets lower so there’s less distortion so their more stable

Question 3

group 2 compounds less thermally stable than group 1 compounds

Answer 3

• greater charge on cation so greater distortion and less stable the carbonate/nitrate compound becomes
• group 2 cations +2 charge less stable than group 1 +1 charge

Question 4

group 1 carbonates

Answer 4

• carbonates are thermally stable which means you can’t heat them enough for them to decompose except from lithium
• LiCo3 Arrow Li2O+Co2

Question 5

Group 1 nitrates

Answer 5

• nitrated decompose to form nitrate and oxygen
• 2MNO3 arrow 2MNO2 + O2
• except LNO3 arrow Li2O + NO2 + O2

Question 6

Group 2 carbonates

Answer 6

• decompose form oxide and carbon dioxide

- MCO3 arrow MO +CO2

Question 7

Group 2 nitrates

Answer 7

• decompose to form oxide, nitrogen dioxide and oxygen

- 2M(NO3) arrow 2MO+4NO2+O2

Question 8

Flame Colour

Answer 8

• li red
• na orange
• k lilac
• rb red
• cs blue
• ca brick red
• sr crimson
• ba green

Question 9

explanation for flame colour

Answer 9

• energy is absorbed from flame causes electrons to move to higher energy levels
• colours seen as electrons fall back down to lower energy levels releasing energy in form of light
• difference in energy between higher and lower levels determine wavelength of light released which determines the colour