Topic 4. Chemistry A level Edexcel

Describe the trend in ionisation energy down group 2.

There is an extra electron shell compared to the one above, extra inner shells shield the outer electrons from the attraction of the nucleus. The extra shells means the outer electrons are further away from the nucleus.

Group 2 react with water to produce?

Hydroxides. M(OH)2

Group 2 burn in oxygen to form?

Oxides MO

Group 2 react with chlorine to form?

Chlorides, MCl2

Explain the trend in reactivity of Group 2 down the group.

Increases. The higher the ionisation energy the less likely they are to react.

Which group 2 oxide is insoluble.

Beryllium oxide

Group 2 oxides react with H20 to form?

Hydroxides M(OH)2

Group 2 oxides react with dilute acid to form?

Salt, MCl2, and H2O

Hydroxides react with water to form?

Hydroxide M(OH)2

Hydroxides react with dilute acid to form?

Salt MCl2 and water

Describe the solubility trend of the hydroxides down group 2.

Solubility increases.

Describe the solubility trend of the group 2 sulphates.

Decreases.

Which group 2 sulphate is insoluble?

Barium sulfate

Explain why thermal stability increases down a group.

As the ionic radius of the cation gets larger they cause less distortion of the anion, due to the lower charge density, thus more stable the carbonate/nitrate compound.

Why are group 2 compounds less thermally stable than group1.

They have a higher charge thus they cause greater distortion to the anion and the less stable the carbonate/nitrate compound becomes.

Group 1 carbonates decompose to form?

Nothing, they are thermally stable.
Except from Lithium: Li2CO3- Li2O and CO2

Which is the exception?

Li2CO3- Li2O and CO2

Group 1 nitrates decompose to form?

Nitrite and oxygen MNO2 + O2

Group 2 carbonates decompose to form?

Oxide and carbon dioxide, MO + CO2

Group 2 Nitrates decompose to form?

Oxide, nitrogen dioxide and oxygen, MO + NO2 + O2

How would you measure the thermal stability of nitrates?

How long it takes for a certain amount of oxygen to be produced. Or the brown NO2 gas.

How would you test the thermal stability of carbonates?

How long it takes for carbon dioxide to be produced. Carbon dioxide bubbled through limewater turns it cloudy.

Flame colour of Lithium

RED

Flame colour of sodium

Orange/yellow

Flame colour for potassium

Lilac

Flame colour for rubidium

Red

Flame colour for caesium

Blue

Flame colour for calcium

Brick-red

Flame colour of Strontium

Crimson

Flame colour of barium

Green

How would you carry out the flame test.

Mix a small amount of the compound being tested with hydrochloric acid. Heat a platinum or nichrome wire in the blue part of the bunsen flame. Dip the wire into the solution and hold it in the blue part of the flame. Note colour produced.

Why do we see colours in the flame test?

The energy absorbed from the flame causes the electrons to move to higher energy levels. When the electrons fall back down to lower energy levels, releasing energy in the form of light. The difference between the higher and lower energy levels determines the wavelength of the light which determines the colour of the light.

Explain the trend of reactivity down group 7,

Down the groups, the atomic radius increases, their outer electrons are further away from the nucleus, and have more shielding. This makes it harder for larger atoms to attract the electron needed to form an ion, therefore larger ions are less reactive.

Explain the trend in electronegativity down group 7.

The increasing number of inner electron shell and the increase in distance between the nucleus and the bonding electrons reduces the atoms ability to attract the bonding pair of electrons.

Explain the trend in melting and boiling points down the group.

Increase. Increase in electron shells and therefore electrons, increasing the force of London forces, which become harder to overcome.

Chlorine will displace...

Both bromide and iodide ions.

Bromine will displace...

Iodide ions

Iodide ions will displace...

Neither chloride or bromide.

What will happen if you mix the reaction mixture with an organic solvent like hexane?

The halogen present will dissolve in the organic solvent, which settles out as a distinct layer.

What colour is chlorine in water?

Virtually colourless

What colour is chlorine in hexane?

Virtually colourless

What colour is bromine in water?

yellow/orange

What colour is bromine in hexane?

Orange/red

What colour is iodine in water?

Brown

What colour is iodine in hexane?

Pink/violet

Halogens are examples of...

Oxidising agents, they themselves are reduced (gain an electron) by oxidised other substances.

Halogens react with group 1 and 2 to produce

Halide salts.

X2 + 2NaOH --\> This is an example of...

NaOX +NaX +H2O.... Disproportionation.

What is bleach? And how is it made?

Sodium chlorate solution. Reacting chlorine gas with cold, dilute aqueous sodium hydroxide.

Another example of disproportionation...

Halogens reacting with hot alkalis. NaXO3 + 5NaX + 3H2O

Chlorine and water undergoes disproportionation too...

Cl2 + H2O --\> HCl + HClO

What is that use of chlorate ions?

They kill bacteria, very useful in water treatment.

Why does the reducing power of the halides increase down the group?

The ions get bigger, so electrons are further away from the positive nucleus, there are extra inner electron shells, so greater effect from shielding, therefore the outer electron can be lost more easily.

KF + H2SO4--\>KHSO4 + HF
KCl + H2SO4--\>KHSO4 + HCl

Misty fumes as HF and HCl comes into contact with moisture in the air. Fluoride and chloride ions aren't strong enough reducing agents to reduce the sulphuric acid so reaction stops.

KBr + H2SO4--\>KHSO4 + Her
2HBr + H2SO4 --\> Br2 + SO2 + 2H2O

Misty fumes of HBr
Bromide ions are stronger reducing agents so react with H2SO4 in a redox.
Produces choking fumes of surfer dioxide and orange fumes of bromine.

KI + H2SO4 --? KHSO4 + HI
2HI + H2SO4 --\> I2 +SO2 + 2H2O
6HI + SO2 --\> H2S +3I2 +2H20

Iodide ions reduce H2SO4. Iodide ions keeps reducing are reduces SO2 to H2S. Which is a toxic, bad egg smelling gas.

What colour will dissolved hydrogen halides turn litmus paper?

Blue as the hydrogen halides are acidic gases.

Outline a test for testing halide ions.

Add dilute nitric acid to remove any ions which might interfere with the reaction. Add silver nitrate solution, a precipitate of the silver halide is formed.

Name the colours of the potential precipitates formed.

Fluoride- np ppt
Chloride- white ppt
Bromide- cream ppt
Iodide- yellow ppt

Describe the reaction of AgCl with ammonia solution.

Ppt dissolves in dilute ammonia solution to give a colourless solution.

Describe the reaction of AgBr with ammonia solution.

ppt remains unchanged if dilute ammonia is added, but will dissolve in concentrated ammonia.

Describe the reaction of AgI in ammonia.

ppt doesn't dissolve even in concentrated.

Outline a test to detect carbonates.

CO32- + 2H+ --\> CO2 + H20
Carbonates will fizz as they give off CO2
HCO3- + H+ --\> CO2 + H20
hsydrogencarbonates will also fizz as they give off CO2.
The CO2 can then be tested by bubbling through limewater, if it goes cloudy CO2 is present, and a carbonate or hydrogen carbonate ion is identified.

Outline a test to test for sulfate ions.

Add HCl, followed by barium chloride solution.
Ba2+ + SO42\- --\>BaSO4
BaSO4 is a white ppt that forms, indicating original compound contained a sulphate.

Outline a test to test for ammonium compounds.

Add sodium hydroxide to substance in test tube and gently heat, if ammonia is given off, it can be tested with a damp piece of red litmus paper, if ammonia is present, it'll dissolve in the water on the paper and turn it blue.
NH4Cl + NaCl --\> NH3 + H20 + NaCl

What is a use for Calcium hydroxide?

(1) is reasonably soluble
in water. It is used in agriculture to
neutralize acidic soils
(2)An aqueous solution of calcium hydroxide
is called lime water and can be used a test
for carbon dioxide. The limewater turns
cloudy as white calcium carbonate is
produced.
Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O(l)