Chapter 8 - reactivity trends Flashcards
what is the key feature of group 2 metals’ electron structure
which subshell are the outer electrons found in
2 outer electrons
the s subshell
why are group 2 metals reducing agents
- when they bond they lose 2 electrons and form a 2+ ion
- they are oxidised
- another species can gain these 2 electrons and be reduced
- thus they are reducing agents
group 2 + oxygen as redox
0 0 +2, -2
2Mg + O2 —–> 2MgO
the magnesium is oxidised
the oxygen is reduced
how do group 2 metals react with water
M + 2H2O —> M(OH)2 + H2
what is the exception to the group 2 reactions with water
magnesium.
it reacts with steam instead and Mg(OH)2 decomposes at high temperatures so the main product is MgO
Mg + H2O —> MgO + H2
what happens when group 2 metals react with acids
they tend to displace the hydrogen to give a metal salt and hydrogen
Mg + 2HCl —> MgCl2 + H2
what is the reactivity trend down group 2 and why
reactivity increases down group 2 because ionisation energy decreases
why does ionisation energy decrease down the group
- atomic radius increases so outer electrons are further from the nucleus, there is less electrostatic attraction
- the greater shielding reduces electrostatic attraction
- the nuclear charge does increase but this is not sufficient to overcome the other two factors so overall ionisation energy decreases
what is the chemical formula for limewater
H2O with Ca(OH)2
list the group 2 metals
Beryllium (Be) Magnesium (Mg) Calcium (Ca) Strontium (Sr) Barium (Ba)
what is the trend in alkalinity and solubility moving down the group for metal hydroxides
both increase
what is the trend is solubility for metal sulfates
it decreases
what is the trend in boiling points of the halogens down the group
bpt increases down the group because they become bigger molecules, this increases the London forces present between molecules, thus more energy is required to overcome them
what sort of agents are the halogens
they are reduced; they gain electrons to form 1- ions
thus they are oxidising agents
appearance of Chlorine, bromine and iodine at RTP
chlorine- pale green gas
bromine - red-brown liquid
iodine - shiny grey-black solid
what can the halogen displacement reactions be used to show
reactivity down the group
the solutions change colour when a reaction takes place
method for halogen-halide displacement reactions
halogens dissolved in water are added to halide salts, if the dissolved halogen is more reactive then it will displace the halide in the salt and the halide in the salt will go into solution
expected results of of the halogen-halide displacement reactions
chlorine will displace bromine and iodine forming orange for bromine and brown/violet for iodine
bromine will only displace iodine forming brown/violet
iodine won’t displace anything
colours of the halogens when in solution with water or an organic substance
water : - chlorine = pale green, bromine = orange, iodine = brown
cyclohexane: chlorine = green, bromine = orange, iodine = violet
how is the displacement reaction of chlorine with sodium bromide a redox reaction
0, +1 , -1, +1, -1, 0
Cl2 + 2NaBr —> 2NaCl + Br2
explain the trends in reactivity of the halogens
- halogens react by gaining electrons
- reactivity decreases down the group because
- atomic radius increases so the electrostatic attraction decreases so its more difficult to gain an electron
- shielding increases so electrostatic attraction decreases, this makes it more difficult to gain electrons and react
- nuclear charge increases but this isn’t sufficient to overcome the other factors
what is the reaction between chlorine and water
Cl2 + H2O —> HClO + HCl
- HClO is a weak bleach
- this is a disproportionation reaction
- litmus paper will turn red then bleach from chlorate ions
what is the reaction between chlorine and dilute, aqueous NaOH
Cl2 + 2NaOH —> NaClO + NaCl + H2O
what are advantages and disadvantages of using chlorine in water purification
- chlorine is used to kill bacteria in water, this makes the water safe to drink and reduces diseases such as cholera
- chlorine is an extremely toxic chemical and if organic matter makes its way into the water system, chlorinated hydrocarbons can form which can cause cancer
explain the carbonate test
1) add dilute nitric acid to your substance in a test tube
2) there may be bubbles
3) bubble these through limewater, if it turns cloudy then carbon dioxide is present thus there was a carbonate
why do we use nitric acid in the carbonate test
it won’t affect future tests
explain the sulphate test
1) add barium nitrate
2) if a sulphate is present then BaSO4 will form
3) this will form a white precipitate
why do we use barium nitrate, and not for example barium chloride
it won’t affect future tests
explain the halide test
1) add aqueous silver nitrate (AgNO3) to your solution
2) precipitates will form: - chloride = white, bromide = cream, iodide = yellow
3) to confirm which is which add dilute ammonia and the chloride precipitate will disappear
4) then add conc. ammonia and the bromide precipitate will dissolve
what is the correct order of the tests
1) carbonate
2) sulphate
3) halide
explain why we use this order for tests
1) neither sulphates or halides will form effervescence in acid so no mistakes can be made
2) BaCO3 would also form a white precipitate so you need to remove the carbonate first
3) Ag2CO3 and Ag2SO4 would form precipitates
explain the test for ammonia
and state the relevant equation
1) add something containing OH- ions
2) warm the mixture- bubbles may be released
3) this gas will turn pH paper blue or damp red litmus blue (or indicator paper)
(NH4+) + (OH-) —> NH3 + H2O
What happens with other halogen disproportionation reactions
E.g. bromine and KOH
They act the same as the chlorine reaction with NaOH
Forming a halogen(ate) salt and a normal metal salt and water
E.g. Br2 + 2KOH —> KBr + KBrO + H2O
What solubility trend do G2 metal oxides have
The same as the hydroxides
They increase in solubility down the group
what is slaked lime and what is it used for
it is calcium hydroxide and it is used to neutralise acidic soil given the group 2 metals are alkaline
what is a barium meal and why is it done
it is where someone consumes barium sulphate in order for x-rays of the gut to be taken given it is completely insoluble and shows up on x-rays
what is milk of magnesia and why is it used
it is magnesium hydroxide and it is used for treating indigestion and heartburn, neutralises stomach acid
what to put when being asked about the reagents for the tests
aqueous
what is the relevant equation for the ammonium ion test
(NH4+) + (OH-) —> NH3 + H2O
what is the relevant equation for the halide test
(Ag+ aq) + (X- aq) —-> AgX (s)
where X represents any halogen
Note: Ag only has a 1+ charge not a 2+ charge
what is the type of reaction where a metal reacts with an acid
REDOX
