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Chemistry module 3 > Chapter 8 - reactivity trends > Flashcards

Chapter 8 - reactivity trends Flashcards

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1
Q

what is the key feature of group 2 metals’ electron structure
which subshell are the outer electrons found in

A

2 outer electrons

the s subshell

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2
Q

why are group 2 metals reducing agents

A
  • 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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3
Q

group 2 + oxygen as redox

A

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

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4
Q

how do group 2 metals react with water

A

M + 2H2O —> M(OH)2 + H2

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5
Q

what is the exception to the group 2 reactions with water

A

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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6
Q

what happens when group 2 metals react with acids

A

they tend to displace the hydrogen to give a metal salt and hydrogen

Mg + 2HCl —> MgCl2 + H2

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7
Q

what is the reactivity trend down group 2 and why

A

reactivity increases down group 2 because ionisation energy decreases

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8
Q

why does ionisation energy decrease down the group

A
  • 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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9
Q

what is the chemical formula for limewater

A

H2O with Ca(OH)2

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10
Q

list the group 2 metals

A 
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
Strontium (Sr)
Barium (Ba)
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11
Q

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

A

both increase

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12
Q

what is the trend is solubility for metal sulfates

A

it decreases

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13
Q

what is the trend in boiling points of the halogens down the group

A

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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14
Q

what sort of agents are the halogens

A

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

thus they are oxidising agents

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15
Q

appearance of Chlorine, bromine and iodine at RTP

A

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

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16
Q

what can the halogen displacement reactions be used to show

A

reactivity down the group

the solutions change colour when a reaction takes place

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17
Q

method for halogen-halide displacement reactions

A

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

18
Q

expected results of of the halogen-halide displacement reactions

A

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

19
Q

colours of the halogens when in solution with water or an organic substance

A

water : - chlorine = pale green, bromine = orange, iodine = brown

cyclohexane: chlorine = green, bromine = orange, iodine = violet

20
Q

how is the displacement reaction of chlorine with sodium bromide a redox reaction

A

0, +1 , -1, +1, -1, 0

Cl2 + 2NaBr —> 2NaCl + Br2

21
Q

explain the trends in reactivity of the halogens

A
  • 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
22
Q

what is the reaction between chlorine and water

A

Cl2 + H2O —> HClO + HCl

  • HClO is a weak bleach
  • this is a disproportionation reaction
  • litmus paper will turn red then bleach from chlorate ions
23
Q

what is the reaction between chlorine and dilute, aqueous NaOH

A

Cl2 + 2NaOH —> NaClO + NaCl + H2O

24
Q

what are advantages and disadvantages of using chlorine in water purification

A
  • 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
25
Q

explain the carbonate test

A

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

26
Q

why do we use nitric acid in the carbonate test

A

it won’t affect future tests

27
Q

explain the sulphate test

A

1) add barium nitrate
2) if a sulphate is present then BaSO4 will form
3) this will form a white precipitate

28
Q

why do we use barium nitrate, and not for example barium chloride

A

it won’t affect future tests

29
Q

explain the halide test

A

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

30
Q

what is the correct order of the tests

A

1) carbonate
2) sulphate
3) halide

31
Q

explain why we use this order for tests

A

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

32
Q

explain the test for ammonia

and state the relevant equation

A

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

33
Q

What happens with other halogen disproportionation reactions

E.g. bromine and KOH

A

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

34
Q

What solubility trend do G2 metal oxides have

A

The same as the hydroxides

They increase in solubility down the group

35
Q

what is slaked lime and what is it used for

A

it is calcium hydroxide and it is used to neutralise acidic soil given the group 2 metals are alkaline

36
Q

what is a barium meal and why is it done

A

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

37
Q

what is milk of magnesia and why is it used

A

it is magnesium hydroxide and it is used for treating indigestion and heartburn, neutralises stomach acid

38
Q

what to put when being asked about the reagents for the tests

A

aqueous

39
Q

what is the relevant equation for the ammonium ion test

A

(NH4+) + (OH-) —> NH3 + H2O

40
Q

what is the relevant equation for the halide test

A

(Ag+ aq) + (X- aq) —-> AgX (s)

where X represents any halogen
Note: Ag only has a 1+ charge not a 2+ charge

41
Q

what is the type of reaction where a metal reacts with an acid

A

REDOX

Chemistry module 3 (4 decks)

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