Chem U2 Flashcards by Simeon Edwards

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

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Reactivity of group 2 elements

Reactivity increases down the group

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Mg burns in steam to produce …

MgO and H2

MgO(s) + H2O(g) —> MgO(s) + H2 (g)

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Mg reacts with water to form…

Magnesium hydroxide Mg(OH)2 + H2

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Group 2 metals react with cold water to form…

Hydroxides and hydrogen

Ca + 2H2O —> Ca(OH)2 + H2

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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

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Solubility in group 2 hydroxides …

Increases down the group

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Oxides of group 2 elements react with acids to form…

Salt and water

MgO + 2HCl —> MgCl2 + H2O

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2HNO3 + Mg(OH)2 —>

Mg(NO3)2 + 2H2O

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Solubility of group 2 hydroxides

Group 2 hydroxides become more soluble down the group

When not soluble, all form white precipitate

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What is the simplistic ionic equation for the formation of Mg(OH)2

Mg2+ + 2OH- —> Mg(OH)2

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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

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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

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What is Ca(OH)2 used for

In agriculture to neutralise acidic soils

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The solubility of group 2 solubility …

Group 2 sulphates become less soluble down the group

BaSO4 being the least soluble

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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

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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