Chapter 8 - reactivity trends Flashcards by Ollie Cooke

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

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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

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group 2 + oxygen as redox

0 0 +2, -2
2Mg + O2 —–> 2MgO
the magnesium is oxidised
the oxygen is reduced

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how do group 2 metals react with water

M + 2H2O —> M(OH)2 + H2

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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

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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

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what is the reactivity trend down group 2 and why

reactivity increases down group 2 because ionisation energy decreases

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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

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what is the chemical formula for limewater

H2O with Ca(OH)2

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list the group 2 metals

Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
Strontium (Sr)
Barium (Ba)

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what is the trend in alkalinity and solubility moving down the group for metal hydroxides

both increase

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what is the trend is solubility for metal sulfates

it decreases

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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

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what sort of agents are the halogens

they are reduced; they gain electrons to form 1- ions

thus they are oxidising agents

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appearance of Chlorine, bromine and iodine at RTP

chlorine- pale green gas
bromine - red-brown liquid
iodine - shiny grey-black solid

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what can the halogen displacement reactions be used to show

reactivity down the group

the solutions change colour when a reaction takes place

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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