Topic 4 Flashcards
What is the equation for the reaction of a Group 2 metal with water?
M (s) + 2H2O (l) —) M(OH)2 (aq) + H2 (g)
What is the equation for the reaction of Group 2 metals burning in oxygen?
2M (s) + O2 (g) —) 2MO (s)
MO is a solid white oxide
What is the equation for the reaction of Group 2 metals with chlorine?
M (s) + Cl (g) —) MCl2 (s)
MCl2 is a solid white chloride
What is the reactivity of Group 2 metals with water as you go down the group?
Be doesn’t react
Mg VERY slow
Ca steadily
Sr fairly quickly
Ba rapidly
What happens to the ionisation energy of Group 2 metals as you go down the group and why?
Decreases.
Extra electron shells
Shield the outer electrons from the attraction of the nucleus
And means that the outer electrons are further away from the nucleus
Outweighs increasing nuclear charge
Reduces electrostatic attraction between nucleus and outer electrons
What does the reaction of Group 2 metal oxides with water form?
Metal hydroxides
How do the hydroxide ions, OH-, in Group 2 metal hydroxides affect the solution?
They make it strongly alkaline
Does beryllium oxide react with water?
No
Is beryllium hydroxide soluble?
No
What is the equation for the reaction of a Group 2 metal oxide with water?
MO (s) + H2O (l) —) M(OH)2 (aq)
What is the equation for the reaction of a Group 2 metal oxide with dilute hydrochloric acid?
MO (s) + 2HCl (aq) —) MCl2 (aq) + H2O (l)
How does the solubility of compounds of Group 2 metals containing singly charged negative ions (e.g. OH-) change down the group?
Increases
How does the solubility of compounds of Group 2 metals containing doubly charged negative ions (e.g. SO4^2-) change down the group?
Decreases
Which Group 2 metal sulphate is insoluble?
Barium sulphate
What is thermal decomposition?
When a substance breaks down when heated. The more thermally stable a substance is, the more heat it will take to break it down.
Why do large cations cause less distortion of carbonate/nitrate ions than small cations?
They have a lower charge density - the charge is spread out over a larger area.
Why are Group 2 carbonates/nitrates less thermally stable than Group 1 carbonates/nitrates?
Greater charge
Greater distortion
Carbonate/nitrate becomes less stable
Are Group 1 carbonates thermally stable?
Yes, you can’t heat them enough with a Bunsen burner to make them decompose
What is the equation for the thermal decomposition of Li2CO3?
Li2CO3 —) Li2O + CO2
What is the equation for the thermal decomposition of Group 1 nitrates?
2MNO3 (s) —) 2MNO2 (s) + O2 (g)
What is the equation for the thermal decomposition of LiNO3?
2LiNO3 —) Li2O + 2NO2 + ½O2
What is the equation for the thermal decomposition of Group 2 carbonates?
MCO3 (s) —) MO (s) + CO2 (g)
What is the equation for the thermal decomposition of Group 2 nitrates?
2M(NO3)2 (s) —) 2MO (s) + 4NO2(g) + O2 (g)
Explain how flame tests for Group 1 and 2 compounds work.
Energy absorbed from flame
Electrons move to higher energy levels
Electrons fall back down to lower energy levels and emit visible light
(Difference in energy between the 2 levels determines the wavelength of the light released - determines the colour of the light)
What colour does lithium produce in a flame test?
Red
What colour does sodium produce in a flame test?
Orange/yellow
What colour does potassium produce in a flame test?
Lilac
What colour does rubidium produce in a flame test?
Red
What colour does Cs produce in a flame test?
Blue
What colour does calcium produce in a flame test?
Brick-red
What colour does Sr produce in a flame test?
Crimson
What colour does Barium produce in a flame test?
Green
How can you test the thermal stability of nitrates?
How easily nitrates decompose can be tested by measuring:
- how long it takes until a certain amount of oxygen is produced (I.e. enough to relight a glowing splint)
- how long it takes until an amount of brown gas (NO2) is produced. (This needs to be done in a fume cupboard, NO2 is toxic)
How can you test the thermal stability if carbonates?
How easily carbonates decompose can be tested by measuring:
- how long it takes for an amount of CO2 to be produced. Bubble through limewater and it will turn cloudy.
