Chem U2 Flashcards
1st ionisation energy
⚡️outermost electrons are held more weakly because they are successively further from the nucleus in additional shells
⚡️outer shell electrons become more shielded from the attraction of the nucleus by the repulsive inner shell electrons
Reactivity of group 2 elements
Reactivity increases down the group
Mg burns in steam to produce …
MgO and H2
MgO(s) + H2O(g) —> MgO(s) + H2 (g)
Mg reacts with water to form…
Magnesium hydroxide Mg(OH)2 + H2
Group 2 metals react with cold water to form…
Hydroxides and hydrogen
Ca + 2H2O —> Ca(OH)2 + H2
Observations from reacting group 2 metals with hydroxides …
Fizzing - more vigorous down the group
Metal dissolving
Solution heating up
With calcium and white precipitate forming
Solubility in group 2 hydroxides …
Increases down the group
Oxides of group 2 elements react with acids to form…
Salt and water
MgO + 2HCl —> MgCl2 + H2O
2HNO3 + Mg(OH)2 —>
Mg(NO3)2 + 2H2O
Solubility of group 2 hydroxides
Group 2 hydroxides become more soluble down the group
When not soluble, all form white precipitate
What is the simplistic ionic equation for the formation of Mg(OH)2
Mg2+ + 2OH- —> Mg(OH)2
A suspension of magnesium hydroxide in water will appear slightly alkaline … So some hydroxide ions therefore ….
Must have been produced by a very slight dissolving
Why is it safe to use magnesium hydroxide in medicine
And
Why is it preferable over calcium carbonate
Because it is so weakly alkaline
It does not produce CO2
What is Ca(OH)2 used for
In agriculture to neutralise acidic soils
The solubility of group 2 solubility …
Group 2 sulphates become less soluble down the group
BaSO4 being the least soluble
If barium metal is reacted with sulphuric acid…
It will only react slowly because the insoluble barium sulphate produced will cover the surface of the metal and act as a barrier to further attack.
Ba+H2SO4—>BaSO4+H2
What is thermal decomposition
The use of heat to break down a reactant into more than one product
Group 2 carbonates decompose to produce …
Group 2 oxides and CO2
MgCO3 —> MgO + CO2
Ease of thermal decomposition increases or decreases down the group 2 carbonates
Decreases
Why are group 2 carbonates more thermally stable as you go down the group
As the cations get bigger they have less of a polarising effect and distort the carbonate ion less.
C-O bond is weakened less so it is less easily broken down
Group 1 carbonates do not decompose with the exception of…
Lithium
Because the ion is small enough to have a polarising effect
Why don’t group 1 carbonated decompose
They only have +1 charge so they don’t have a big enough charge density to polarise the carbonate ion.
What is a experiment to investigate the ease of decomposition
Hear known mass if carbonate in side arm boiling tube
Pass produced gas through lime water
Time for first appearance of cloudiness in limewater
Repeat with different carbonates using
SAME MOLES OF CARBONATE
SAME VOLUME OF LIMEWATER
SAME BUNSEN FLAME AND HEIGHT
What forms from thermal decomposition of group 2 nitrates
Group 2 oxides
Nitrogen dioxide
Oxygen
2Mg(NO3)2 —> 2MgO+4NO2+O2
What would you observe from the decomposition of group 2 nitrates
Brown gas- NO2
White nitrate solid melts to colourless and then resoludifies
The ease of thermal decomposition of group 2 nitrates …
Decreases down the group
Why does magnesium nitrate decompose the easiest
Because the mg2+ ion is the smallest and therefore has the greatest charge density.
Causes more polarisation of the nitrate anion and weakens the N-O bond
Group 1 nitrates do not decompose with the exception of lithium, they decompose to give…
Nitrate(3) salt and oxygen.
Explanation of the occurrence of flames in flame test
Hear causes the electron to move to a higher energy level
Electron is unstable at a higher energy level and so drops back down
As it drops back down from the higher to a lower energy level, energy is emitted in the form of a visible light with the wavelength of the observed light
Trend in melting point and boiling point
Melting/Boiling points increase down the group
Molecules become larger as they have more electrons, so have higher London forces between the molecules.
As the intermolecular forces get larger more energy is required to break the forces, increasing boiling and melting temps .
Oxidising agents are…
Electron acceptors
Oxidising strength…
Decreases down the group
Melting points for Group 2 elements
?Melting points decrease down the group
?Metallic bonding weakens as the atomic size increases
?Distance between the positive ions and delocalised electrons increase
?Causing the electrostatic forces of attraction between positive ions and delocalised electrons to weaken
Le Chateliers principal states that
If an external condition is changed the equilibrium will shift to oppose that change
N2 + 3H2 —> 2NH3
=-ve exo
What effect would increasing the temperature have on the yield of ammonia
If temperature was increased the EQUILIBRIUM WILL SHIFT TO OPPOSE this and move to the ENDOTHERMIC BACKWARDS REACTION to try to DECREASE TEMPERATURE. The position of equilibrium would SHIFT TO THE LEFT giving a LOWER YIELD OF AMMONIA
In equilibrium, increasing pressure will…
Cause the equilibrium to shift to the side with the FEWER MOLES of gas to OPPOSE the change and REDUCE the pressure
According to le chatelier , decreasing pressure will..
Cause equilibrium to shift to the side with the most moles of gas to OPPOSE the change and therefore increase the pressure
What effect would increasing the pressure have on methanol
CO(g) + 2H2(g) —>CH3OH(g)
If pressure is increased the equilibrium would shift go oppose this and shift to the side with the FEWER MOLES to try to reduce the pressure
The position of equilibrium would shift to the right because there are 3 moles of gas on the left but only one mole of gas on the right giving a higher yield of methanol
Catalyst on equilibrium
Catalyst has no effect on the position of equilibrium but will speed up the rate at which equilibrium is achieved
Why doesn’t a catalyst effect the position of equilibrium
Because it speeds up the rate if the forward and backward reactions by the same amount
