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A-level Chemistry > 3.2 - Group 2 and the halogens > Flashcards

3.2 - Group 2 and the halogens Flashcards

1
Q

What is the electron configuration of the outer shell of group 2 elements ?

A
  • Each group 2 element contains 2 outer shell electrons
  • The two electrons are in the outer s sub-shell ( s^2 )
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2
Q

What do group 2 elements do during redox reactions ?

A

They lose two outer shell electrons to form 2+ ions

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3
Q

Explain how group 2 elements are reducing agents ?

A
  • Each metal atom is oxidised, losing two electros to form a +2 ion
  • Another species will gain these two electrons and be reduced
  • Group 2 elements are therefore reducing agents as they reduce another species
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4
Q

Write the half equation showing a group 2 element being oxidised ?

A

X –> X^2+ + 2e-

eg. Ca –> Ca^2+ + 2e-

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5
Q

What happens during redox reactions of group 2 elements with oxygen ?

A

Group 2 elements all react with oxygen to form a metal oxide with the general formula XO

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6
Q

Write the equation for a redox reaction of group 2 elements with oxygen ?

A

2X + Ov2 –> 2XO

eg. 2Mg(s) + Ov2(g) –> 2MgO(s)

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7
Q

What happens during redox reactions of group 2 elements with water ?

A

Group 2 elements react with water to form an alkaline hydroxide with general formula X(OH)v2, and hydrogen gas

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8
Q

Write the equation for a redox reaction of group 2 elements with water ?

A

X + Hv2O –> X(OH)v2 + Hv2

eg. Sr(s) + Hv2O(l) –> Sr(OH)v2(aq) + Hv2(g)

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9
Q

What happens during redox reactions of metals with dilute acids ?

A

Metals react with dilute acids to form a salt and hydrogen

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10
Q

Write the equation for a redox reaction between metals and dilute acids ?

A

Metal + acid –> salt + hydrogen

eg. Mg(s) + 2HCl(aq) –> MgClv2(aq) + Hv2(g)

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11
Q

What is the trend in reactivity of group 2 elements ?

A

As you go down the group, the reactivity of group 2 elements increases

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12
Q

Explain the trend in relativity of group 2 elements in terms of first and second ionisation energy ?

A
  • As you go down the group, the number of electron shells increases meaning the atomic radius and shielding increases
  • This means there is a greater number of repealing electrons and distance between the outer shell electrons and the positive nucleus
  • This means that the outer shell electrons are less attracted to the positive nucleus causing the first and second ionisation energy to decrease
  • This means less energy is required to remove the first and second outer electrons to form a 2+ ion, causing reactivity to increase
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13
Q

What happens during reactions between group 2 compounds and water ?

A

The oxides of group 2 elements react with water, releasing OH- ions forming an alkaline solution of metal hydroxide

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14
Q

Write an equation for the reaction between group 2 compounds and water ?

A

XO + Hv2O –> X(OH)v2

eg. CaO(s) + Hv2O(l) –> Ca(OH)v2(s)

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15
Q

What is the trend in solubility and alkalinity of group 2 hydroxides ?

A
  • As you go down the group , the solubility of group 2 hydroxides in water increases
  • This means the group 2 oxides release more OH- ions resulting in solution containing more OH- increasing it’d pH/ alkalinity
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16
Q

What are the uses of group 2 compounds as bases ?

A
  • Ca(OH)v2 in agriculture to neutralise acid soils
  • Mg(OH)v2 and CaCOv3 as ‘antacids’ in treating indigestion.
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17
Q

Explain how group 2 compounds are used as bases in agriculture ?

A

Ca(OH)v2 is added to fields as lime by farmers to increase the pH and neutralise acidic soils, forming neutral water

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18
Q

Write the equation showing group 2 compounds being used as bases in agriculture ?

A

Ca(OH)v2(s) + 2H+(aq) –> Ca2+(aq) + 2Hv2O(l)

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19
Q

Explain ho group 2 compounds are used as bases in medicine ?

A

Group 2 bases are often used as antacids for treating acid indigestion ( ie. Mg(OH)v2 and CaCOv3 )

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20
Q

Write the equations showing group 2 compounds being used as bases in medicine ?

A

Mg(OH)v2(s) + 2HCl(aq) –> MgClv2(aq) + 2Hv2O(l)

CaCOv3(s) + 2HCl(aq) –> CaClv2(aq) + Hv2O(l) + COv2(g)

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21
Q

What is the electron configuration of the outer shell of group 7 elements ?

A
  • Each halogen has 7 outer-shell electrons, two are in the outer s sub shell and five are in the outer p sub-shell ( s^2p^5 )
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22
Q

What do group 7 elements do during redox reactions ?

A
  • Each halogen atom is reduced, gaining one electron to form a -1 halide ion
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23
Q

Explain how group 7 elements are oxidising agents ?

A
  • Each halogen atom is reduced, gaining an electron to form a -1 halide ion
  • Another species loses electrons to halogen atoms and is oxidised
  • Group 7 elements are therefore oxidising agents as they oxidise another species
24
Q

Write the half equation showing a group 7 element being reduced ?

A

Xv2 + 2e- –> 2X-

eg. Fv2 + 2e- –> 2F-

25
Q

What is the trend in boiling points for group 7 elements ?

A

As you go down the group, the boiling point increases

26
Q

Explain the trend in boiling points of group 7 elements ?

A
  • Halogens exist as diatomic molecules
  • As you go down the group, there is a greater number of electron shells meaning the size of the molecule increases
  • This means there is a greater number of electrons present resting in stronger induced dipoles
  • This results in stronger London forces between molecules which require more energy to overcome and separate molecules
  • This causes the boiling point to increase
27
Q

Name the various halogens and their appearance/state at room temperature ?

A
28
Q

What is the trend in reactivity of group 7 elements ?

A

As you go down the group, the reactivity of group 7 elements decreases

29
Q

Explain the trend in reactivity of group 7 elements ?

A
  • As you go down the group, the number of outer electron shells increases meaning the atomic radius and shielding increases
  • This means there is a greater number of repealing electrons and greater distance between the outer shell electrons and positive nucleus
  • This means there is weaker attraction between the outer shell electrons and positive nucleus meaning is harder to gain an electron since it is less attracted to the positive nucleus
  • This causes the reactivity to decrease
30
Q

What type of reactions show the trend in reactivity of group 7 elements ?

A

Halogen displacement reactions with halide ions

31
Q

What happens during halogen displacement reactions with halide ions ?

A
  • During the displacement reaction, the more reactive halogen will displace the less reactive halide from it salt
  • This results in the formation of the less reactive halogen
32
Q

What are the colours halogen solutions in water during halogen displacement reactions?

A

Chlorine = pale green solution in water
Bromine = Orange solution in water
Iodine = Brown solution in water

33
Q

Why is cyclohexane used during the halogen displacement reaction with halide ions ?

A
  • Aqueous solutions of bromine and iodine can be difficult to tell apart due to having a similar orange-brown colour
  • Cyclohexane is therefore used to tell them apart
34
Q

What are the colours halogen solutions in cycloalkane during halogen displacement reactions ?

A

Chlorine = pale green solution in cyclohexane
Bromine = orange solution in cycloalkane
Iodine = violet solution in cycloalkane

35
Q

What apparatus can be used to separate the layers ?

A

Separating funnel

36
Q

What are the results of halogen displacement reactions ?

A
  • Chlorine reacts with both Br- and I- ions
  • Bromine only reacts with I- ions
  • Iodine react with neither ions
37
Q

Write the full and ionic equation for the displacement reaction between chlorine solution and sodium bromide ?

A

Clv2(aq) + 2NaBr(aq) –> 2NaCI(aq) + Brv2(aq)

Clv2(aq) + 2Br- (aq) –> 2Cl- (aq) + Brv2(aq)

38
Q

Write the full and ionic equation for the displacement reaction between chlorine solution and sodium iodide ?

A

Clv2(aq) + 2NaI(aq) –> 2NaCI(aq) + Iv2(aq)

Clv2(aq) + 2I- (aq) –> 2Cl- (aq) + Iv2(aq)

39
Q

Write the full and ionic equation for the displacement reaction between bromine solution and sodium iodide ?

A

Brv2(aq) + 2NaI(aq) –> 2NaBr(aq) + Iv2(aq)

Brv2(aq) + 2I- (aq) –> 2Br- (aq) + Iv2(aq)

40
Q

What is a disproportionation reaction ?

A

It is a redox reaction where the same element is both oxidised and reduced

41
Q

What are the benefits of using chlorine ?

A
  • Chlorine can be used in water treatment to kill/ destroy bacteria
  • Chlorine can be used to produce a household bleach
42
Q

Explain how chlorine is used in water treatment to kill harmful bacteria ?

A
  • When chlorine reacts with water, a disproportionation reaction occurs producing HClO ( hydrogen chlorate (l) ) and HCl ( hydrochloric acid )
  • HClO is responsible for killing harmful bacteria
43
Q

Explain another role that HClO has ?

A
  • HClO is also a weak bleach
  • Therefore, in the presence of damp blue litmus paper it will turn it ed before turning it white
44
Q

Write the equation for chlorine reacting with water when used in water treatment to kill bacteria ?

A

Clv2(aq) + Hv2O(l) -> HCIO(aq) + HCI(aq)

45
Q

Explain how chlorine can be used to produce household bleach ?

A
  • When chlorine reacts with cold AND DILUTE NaOH/ sodium hydroxide solution, a disproportionation reaction occurs
  • This results in NaClO ( sodium chlorate (l) ), NaCl and Hv2O being produced
  • NaClO has high concentration of ClO- / chlorate ions meaning it can act as a household bleach
46
Q

What are the conditions for making household bleach using chlorine ?

A

Cold and dilute aqueous sodium hydroxide ( NaOH )

47
Q

Write the equation for chlorine being used to produce household bleach ?

A

CIv2(aq) + 2NaOH(aq) -+ NaCIO(aq) + NaCI(aq) + Hv20(l)

48
Q

Can you explain how chlorine reacting with water and cold sodium hydroxide solution is a disproportionation reaction ?

A

Yes

49
Q

What are the risks of chlorine ?

A
  • Chlorine is an extremely toxic gas
  • Chlorine can react with hydrocarbons to produce chlorinated hydrocarbons which are possible carcinogens
50
Q

Explain the risks of chlorine with regards to it being an extremely toxic gas ?

A
  • Chlorine is an extremely toxic gas
  • In small concentrations, it can act as respiratory irritant
  • In large concentrations is can be fatal/ lead to death
51
Q

Explain the risks of chlorine with regards to it producing chlorinated hydrocarbons ?

A
  • In drinking water, chlorine can react with organic matter ( eg. methane from decaying vegetation ) in a free radical substitution reaction
  • This can produce chlorinated hydrocarbons which are possible carcinogens which cause cancer
52
Q

What is chlorine used despite its high risks ?

A
  • If chlorine is not used to treat water, we risk bacteria flourishing which can lead to terrible diseases such as cholera of typhoid
  • Providing a clean water supply is vital, if chlorine were not used this would be compromised
53
Q

What is used to test for the presence of halogens ?

A

Aqueous silver nitrate solution [ AgNOv3 (aq) ]

54
Q

Describe how to test for halides ?

A
  • Add aqueous silver nitrate solution [ AgNOv3 ( aq ) ] to an aqueous solution of a halide
  • Note the colour of the precipitate that forms
  • Add aqueous ammonia to test the solubility of the precipitate
55
Q

What are the colours of the precipitate when aqueous silver nitrate is added to aqueous solution of a halide ?

A

Chlorine = White precipitate
Bromine = Cream precipitate
Iodine = Yellow precipitate

56
Q

Why is aqueous ammonia used to test the solubility of the precipitate ?

A
  • This is a confirmative test used to tell the different precipitate colours apart
  • White, cream and yellow can be easily misinterpreted
57
Q

What is the solubility of the different precipitates when aqueous ammonia is added ?

A

A-level Chemistry (31 decks)

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