Studied by 3 people
How does Group 2 react with water?
To form a metal hydroxide and hydrogen
How does Group 2 react with oxygen?
They burn to form solid white metal oxides.
How does Group 2 react with chlorine?
They react to form solid white metal chlorides.
How does a Group 2 metal oxide react with water? What are the exceptions to this?
What do Group 2 metal oxides and hydroxides therefore do in acids?
They react to form metal hydroxides, which then dissolve with the OH- ions making the resulting solution strongly alkaline. The hydroxides get more soluble as you go down the group, so the solutions get more alkaline.
Beryllium oxide is an exception- it does not react with water, and beryllium hydroxide is insoluble.
Magnesium oxide is an exception- it reacts slowly and the hydroxide is not very soluble.
Group 2 metal oxides and hydroxides with neutralise acids.
What happens to reactivity down Group 2?
Increases.
What is the equation for the reaction between magnesium oxide and hydrochloric acid?
MgO (s) + 2HCl (aq)→ MgCl2 (aq)+ H20 (l)
What happens to the solubility of compounds of Group 2 elements with singly charged negative ions (eg. OH-) down the group?
Solubility increases.
What happens to the solubility of compounds of Group 2 elements with doubly charged negative ions (eg. SO4 2-) down the group?
decreases.
What about barium sulfate is unusual in terms of solubility?
It is insoluble.
What is thermal decomposition and thermal stability?
Thermal decomposition is where a substances breaks down on heating.
Thermal stability is how much heat is needed to break the substance down. The more thermally stable a substance is, the more heat is needed.
Why does the thermal stability of nitrates and carbonates increase down a group?
Carbonate and nitrate ions are made less stable in by the presence of cations as the cation polarises the anion, distorting it. The greater the distortion, the less stable a compound is. Large cations cause less distortion as they have a lower charge density.
Why are Group 2 compounds less thermally stable than Group 1 compounds?
The greater the charge on the cation, the greater the distortion and the less stable the compound becomes. Group 2 cations have a 2+ charge while Group 1 cations have a 1+ charge.
What is the thermal stability of Group 1 carbonates? What is the exception?
Group 1 carbonates are thermally stable and cannot be heated enough with a bunsen burner to make them decompose.
The exception is lithium carbonate, which decomposes into lithium oxide and carbon dioxide.
What is the thermal stability of Group 2 carbonates? What is the exception?
Group 2 carbonates are less thermally stable than Group 1 carbonates, and will decompose into the metal oxide and carbon dioxide.
What is the thermal stability of Group 1 nitrates? What is the exception?
Group 1 nitrates decompose to form the nitrite (NO2) and oxygen.
The exception is lithium nitrate which decomposes to form lithium oxide, nitrogen dioxide and oxygen.
What is the thermal stability of Group 2 nitrates?
Group 2 nitrates decompose to form the oxide, nitrogen dioxide and oxygen.
How can you test how easily nitrates decompose?
How long it takes for a certain amount of oxygen to be produced (Group 1)
How long it takes for a certain amount of nitrogen dioxide to be produced (a toxic brown gas- needs to be done in a fume cupboard) (Group 2).
How can you test how easily carbonates decompose?
How long it takes for an amount of carbon dioxide to be produced (Group 2)
How do you carry out a flame test?
mix a small amount of the compound with a few drops of HCl.
Heat a platinum or nichrome wire in the flame to clean it.
Dip the wire in the mixture, hold it in a hot flame and note the colour produced.
What colour do lithium and rubidium produce in the flame test?
red
What colour does sodium produce in the flame test?
orange/yellow
What colour does potassium produce in the flame test?
lilac
What colour does caesium produce in the flame test?
blue
What colour does calcium produce in the flame test?
brick red
What colour does strontium produce in the flame test?
crimson
What colour does barium produce in the flame test?
green
Why are colours produced in the flame test?
The energy absorbed from the flame causes electrons to move to higher energy levels, and the colours are seen as the electrons drop back to their original energy level and this releases energy as light. The colour is determined by the wavelength of the light released, which is determined by the difference in energy between the higher and lower energy levels.
Why do halogens in their natural state have low solubility in water?
They are non-polar
What colour is fluorine gas?
Pale yellow
What colour is chlorine gas?
Green
What colour is bromine liquid?
Red-brown
What colour is solid iodine?
Grey
What colour is chlorine when dissolved in water and dissolved in hexane?
Colourless in both
What colour is bromine when dissolved in water and dissolved in hexane?
Yellow-orange in water and orange-red in hexane
What colour is iodine when dissolved in water and dissolved in hexane?
Brown in water, pink-violet in hexane.
Why do halogens get less reactive down the group?
Halogen atoms usually react by gaining an electron in their outer p subshell. As you go down the group, atoms get larger so outer electrons are further from the nucleus and there is more electron shielding. This makes it harder for larger atoms to attract the electron needed to react.
Why do melting and boiling points increase down group 7?
Down group 7, there is an increase in electron shells and therefore electrons, so the London forces between molecules get stronger. Stronger London forces means the intermolecular forces are harder to overcome and so melting and boiling points increase.
Why is it hard to study the chemistry of fluorine and astatine?
Fluorine is toxic and astatine is very radioactive.
The reaction Cl2 (aq) + 2KBr (aq) occurs. What type of reaction is this and what is the product? What characteristic of group 7 does this display?
2KCl (aq) + Br2 (aq)
Displacement reaction
Halogens can displace less reactive halide ions from solution.
What type of reaction occurs between halogens and halides?
Redox reactions (and displacement)
What will you see if a redox reaction takes place in solution (halogen reacting with halides)? How can you make this easier to see?
A colour change.
If bromide is displaced and Br2 is formed, the reaction mixture will turn orange.
If iodide is displaced and I2 is formed, the reaction mixture will turn brown.
This can be made easier to see by shaking with an organic solvent like hexane, which will cause the halogen to dissolve in the organic solvent and form a distinct layer above the aq.
How do halogens react with group 1 and group 2?
A redox reaction occurs- the halogen is reduced and the metal is oxidised.
What is the product of the reaction Mg (s) + Cl2 (g)?
MgCl2
Magnesium is oxidised- Mg to Mg2+
Chlorine is reduced- Cl2 to 2Cl-
How do halogens react with cold alkalis?
A disproportionation reaction will occur. The halogen is both oxidised and reduced.
Iodine reacts with cold, dilute sodium hydroxide. What are the products?
NaOI + NaI + H20
What are the general products of the reaction between any halogen and cold, dilute sodium hydroxide?
X2 + 2NaOH goes to NaOX + NaX + H20
Why can halogens undergo disproportionation when reacting with cold, dilute alkalis?
Halogens except fluorine can exist in a wide range of oxidation states.
What is the main dangerous product if you react chlorine with cold, dilute sodium hydroxide?
Bleach- NaClO
How do halogens react with hot alkalis? What is the general formula for this reaction?
Disproportionation
3X2 + 6NaOH goes to NaXO3 +5NaX +3H2O
(Na can be replaced with any other alkali)
