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Aqa a level chemistry > Topic 8: Group 2 and Group 7 > Flashcards

Topic 8: Group 2 and Group 7 Flashcards

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1
Q

State one observation when magnesium reacts with steam

A

White solid forms

Mg (s) + H2O (g) –> MgO (s) + H2 (g)

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2
Q

what is the equation for when barium reacts with water and evidence for the formation of barium hydroxide

A

Ba (s) + 2H2O (l) –> Ba(OH)2 (aq) + H2 (g)

-fizzing shows formation of hydrogen gas
-litmus paper can be used to show alkaline solution

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3
Q

contrast these observations with those for calcium with water

A

-when calcium reacts with water a solid suspension is formed rather than aqueous as calcium is less soluble and less alkaline
-Calcium reacts less vigorously

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4
Q

what happens to hydroxides and sulfates down group 2

A

hydroxides are more soluble
sulfates are less soluble down group 2

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5
Q

what is the correct observation when barium metal is added to an excess of water

A

forms a colourless solution and effervesces

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6
Q

which compound is used to treat symptoms of indigestion

A

Mg(OH)2

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7
Q

equation for stronium with cold water

A

Sr (s) + 2H2O (l) –> Sr(OH)2 (aq) + H2 (g)

aqueous formed as more soluble

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8
Q

describe what you would see if you dropped some pieces of calcium into cold water

A

-vigorous reaction producing a colourless gas
-calcium would disappear to leave a white precipitate in a colourless solution

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9
Q

what is the least reactive element in group 2 and why

A

Be (Beryllium) is the least reactive element in group 2 as it has the smallest atomic radius, least shielding and the same nuclear charge. This means that there are stronger electrostatic forces of attraction

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10
Q

reactions with water (1)

A

-Mg to Ba in group 2 react with water

-As you go down group rate of reaction increases

-As you go down group 2 reactivity with water increases (Barium reacts most vigorously with water)

Mg (s) + 2H2O (l) —> Mg(OH)2 (s) + H2 (g)

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11
Q

what happens to reactivity down group 2

A

increases

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12
Q

group 2 reactions with water (2)

A

Mg –> very slow reaction with cold water

Ca –> fizzes and milky white alkaline suspension formed (solid)

Sr –> Fizzes vigorously and alkaline solution (aqueous)

Ba –> Fizzes very vigorously and strongly alkaline solution (aqueous)

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13
Q

magnesium reacting with steam

A

Magnesium reacts more rapidly with water when its steam to form a white solid and burns with a bright, white light

Mg (s) + H2O (g) –> MgO (s) + H2 (g)

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14
Q

why does beryllium not react with water

A

Beryllium doesn’t react with water as it has an insoluble surface oxide layer

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15
Q

reactions of Mg,Ca,Sr

A

reacts with oxygen to form metal oxide MgO

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16
Q

Ba reacts with excess oxygen to form what

A

Ba reacts with excess oxygen to form BaO2

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17
Q

group 2 metals react with chlorine to form

A

-all group 2 metals react with chlorine to form XCl2 e.g BaCl2

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18
Q

Group 2 metals (not including Be) react with water to form

A

-Mg – Ba reacts with water to form a metal hydroxide with hydrogen e.g Mg(OH)2 + H2

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19
Q

group 2 oxides reacting with water

A

-Group 2 oxides react with water but they do not fizz so no hydrogen gas is formed

g MgO (s) + H2O (l) –> Mg(OH)2 (s)

Metal oxide + water –> metal hydroxide

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20
Q

what forms when group 2 oxides e.g MgO react with water

A

BeO –> No reaction

MgO –> Little reaction, slightly alkaline suspension

CaO –> White, weakly alkaline suspension (pH 10)

SrO –> Colourless, alkaline solution (pH 12)

BaO –> Colourless, very alkaline solution (pH 14)

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21
Q

hydroxides

A

-Hydroxides become more soluble as you go down the group to form alkaline solutions

-Solubility increases as alkalinity increase (more OH- ions)

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22
Q

calcium hydroxide

A

Calcium hydroxide is only slightly soluble in water and forms a solution called limewater. Lime water is used to test for carbon dioxide; it turns cloudy when CO2 has bubbled through it. It turns cloudy as it forms a white precipitate known as calcium carbonate which is insoluble in water

Ca(OH)2 + CO2 –> CaCO3

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23
Q

soluble vs insoluble hydroxides

A

Ba and Sr = soluble (aq)
Mg and Be = insoluble (s)

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24
Q

soluble vs insoluble sulfates

A

Be and Mg = soluble
Ba and Sr = insoluble

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25
Q

barium sulfates

A

-Barium sulfate is used as a radiocontrast agent to help take x-ray images of the digestive system. It is a very good absorber of x-rays so therefore helps to define structures of the digestive system to aid diagnosis.

-Barium sulfate is used as it is insoluble so it is not absorbed by the body when swallowed.

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26
Q

uses of group 2 metals

A

Mg is used to extract Ti from TiCl4 as Mg is more reactive than Ti so displacement reaction occurs

Mg(OH)2 is used to treat indigestion as it neutralises acid reflux.

Ca(OH2) is used to raise the pH of acidic soil as it is alkaline so neutralises soil

CaO and CaCO3 are used to remove SO2 from flue gases as SO2 is acidic so reacts with basic compounds (alkaline)

BaSO4 used as an x-ray contrast agent in the body

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27
Q

Explain why iodine forms essentially covalent compounds with metals

A

-iodine is a large anion so has a greater electron cloud and atomic radius
-this means that there is an overlap of electron density which leads to the compounds being essentially covalent

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28
Q

Explain why flourine forms ionic compounds with hydrogen

A

-flourine is very electronegative which means covalent bond is so polarised that electrons are essentially fully transferred

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29
Q

true or false - group 7 elements are diatomic

A

true

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30
Q

what happens to reactivity as you go down the group 7

A

decreases as it becomes harder to add an electron

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31
Q

colours of bromine, chlorine and iodine

A

Chlorine = green-yellow gas

-Bromine = dark red liquid

-Iodine = dark grey solid

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32
Q

group 7

A

All four of the main halogens are reactive non-metals

-Flourine and chlorine are the most reaction elements in group 7

-the stronger the intermolecular force, the higher the boiling point

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33
Q

why does the boiling point of halogens increase down group 7

A

Halogens increase in boiling point as we go down the group as there are more electrons per molecule so stronger van der waal forces between molecules which require more energy to overcome

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34
Q

cl-cl bond

A

Cl-Cl = same electronegativity so is non-polar

Halogens = anions

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35
Q

Group 7 halogens colour in aqueous and vapor

A

Flourine (gas) = pale yellow but yellow vapour

Chlorine (gas) = pale green but green vapour

Bromine (liquid) = orange and orange vapour

Iodine (solid) = grey but purple vapour

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36
Q

halogens dissolve freely in hydrocarbon solvents

A

Halogens dissolve freely in hydrocarbon solvents such as cyclohexane and they produce the colours of their vapours e.g iodine = purple

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37
Q

why does flourine attract the most electrons

A

Flourine would attract electrons the most easily as it has the highest electronegativity and the smallest atomic radius/less shielding which means greater electrostatic force of attraction so most oxidising.

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38
Q

why are halogen bonds essentially covalent

A

Due to its large size, iodine is heavily polarised when placed next to a small cation such as Li+. This means that compounds are essentially covalent.

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39
Q

displacement reaction

A

-a more reactive halogen will displace a less reactive halide from its compound

-most displacement reactions occur in an aqueous solution

e.g Flourine displaces iodine from potassium iodide

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40
Q

displacement observations

A

Displacement observations (colour of halogen released)

-Chlorine = pale green

-Bromine = orange

-Iodine = brown

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41
Q

testing for halides

A

-halides = negative anions

-Halides are colourless ions which we can test for by adding aqueous silver nitrate solution (AgNO3)

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42
Q

halide precipitate colours

A

-Chloride = white precipitate

-Bromide = cream precipitate

-Iodide = yellow precipitate

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43
Q

steps of halide test

A

1) Add nitric acid to remove carbonate impurities

2) Add a few drops of silver nitrate solution

3) Chloride ions would form a white precipitate of silver

4) Bromide ions would form a cream precipitate of silver bromide

5) Iodide ions would form a yellow precipitate of silver iodide

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44
Q

distinguish between precipitates

A

-We can add aqueous ammonia to the precipitate of silver halide

1) Add ammonia solution to the precipitate

2) AgCl would dissolve in both a dilute and concentrated ammonia

3) AgBr would only dissolve in concentrated ammonia

4) AgI wouldn’t dissolve in dilute or concentrated ammonia

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45
Q

Describe a further test to show whether solution C contains chloride or bromide ions

A

-add dilute ammonia solution
-if precipitate dissolves chloride ions are present
-not dissolve = bromide ions

46
Q

what type of gas is formed and how to test for it

A

CO2

when bubbled through lime water a white precipitate is formed

47
Q

explain how the observations from test 1 and 2 can be used to show that solution B has HCL

A

-effervescence = H+ ions
-white precipitate of silver chloride due to adding aqueous silver nitrate so contains chloride ions

48
Q

describe a series of tests that the student can use to show that solution C contains ammonia sulfate

A

-warm solution with some NaOh
-damp red litmus turns blue
-add acidified BaCl2
-white precipitate formed

49
Q

suggest the identity of the positive ion in solution A

Give the simplest ionic equation

A

Ba2+

Ba2+ + SO42- –> BaSO4

50
Q

what gas turned litmus paper blue from red

A

ammonia

51
Q

what property increases down group 7

A

boiling point

52
Q

state what is observed when silver nitrate solution is added to sodium flouride solution

A

no precipitate formed

53
Q

what colour precipitate is formed by oxides

A

white

54
Q

what are group 2 oxides and hydroxides

A

bases

55
Q

why is group 7 less reactive as you go down

A

harder to gain an electron and form an ion (weaker attraction)

56
Q

state why magnesium hydroxide solution should not be used in titration of weak acids

A

-Mg(OH)2 = insoluble

57
Q

why should water not be used to put out a fire in which magnesium metal is burning

A

-hydrogen is produced when group 2 metal put in water
-hydrogen is flammable

58
Q

metal carbonate + acid

A

carbon dioxide + water + salt

59
Q

what does effervescence in an acidic solution mean

A

presence of H+ ions

60
Q

Describe a series of tests that the student can use to show that solution C contains ammonium sulfate

A

-warm with some NaOH
-damp red litmus at mouth of tube turns blue
-add acidified BaCl2
-white precipitate formed

61
Q

Explain how the masses recorded during this experiment can be used to show that solution D contains a mixture of halide ions

A

-the 2nd mass is smaller –> mass after step 4 smaller than mass after step 2
-AgCl dissolves in dilute ammonia

62
Q

reactions with sodium halides

A

-we can observe the differences in reducing power of a halide by reacting solid sodium halides with concentrated sulfuric acid

1) Add concentrated sulfuric acid to the solid halide
2) Sulfuric acid displaces the weaker acids HCl, HBr and Hi from their salts
3) Hydrogen halides all form fumes in moist air
4) As they become more powerful reducing agents down the group, they can react further by reducing the sulfuric acid to a lower oxidation state of sulfur

63
Q

Cl- (halide)

A

HCl (products) –> steamy fumes

64
Q

Br-

A

HBr –> steamy fumes
Br2 –> brown fumes
SO2 –> colourless gas

65
Q

I-

A

Hi –> steamy fumes
I2 –> purple fumes
SO2 -> colourless gas
S –> yellow solid
H2S –> gas (bad egg smell)

66
Q

H2SO4

A

Concentrated sulfuric acid can react as both an acid and an oxidising agent

67
Q

formation of hydrogen halides

A

NaX + H2SO4 –> NaHSO4 + HX

68
Q

explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in this test for iodide ions

A

HCl would form a white precipitate

69
Q

write an equation for the reaction of chlorine with cold water

A

Cl2 + H2O –> HClO + HCl

70
Q

oxidising power down group 7
(oxidising agent)

A

Fluorine is the strongest oxidizing agent because fluorine atoms are the smallest halogen atoms, and so accept electrons most easily. Down group 7, as the halogen atoms get larger, they accept electrons less easily, and the oxidizing power becomes weaker.

71
Q

chlorine + water

A

chlorine with water to form chloride ions and chlorate(I) ions.

72
Q

group 2 melting point

A

Melting points decrease down the group. The metallic
bonding weakens as the atomic size increases. The
distance between the positive ions and delocalized
electrons increases. Therefore the electrostatic
attractive forces between the positive ions and the
delocalized electrons

73
Q

magnesium with steam vs warm water

A

steam = produces MgO + H2

warm water = produces (MgOH)2 + H2

74
Q

group 2 with cold water
Ca, Sr, Ba

A

The other group 2 metals will react with cold water with
increasing vigour down the group to form hydroxides. Ca + 2 H2O (l) Ca(OH)2
(aq) + H2
(g)
Sr + 2 H2O (l) Sr(OH)2
(aq) + H2
(g)
Ba + 2 H2O (l) Ba(OH)2
(aq) + H2
(g)

75
Q

observations when group 2 reacts with cold water

A

fizzing, (more vigorous down group) the metal dissolving, (faster down group) the solution heating up (more down group) with calcium a white precipitate appearing
(less precipitate forms down group with
other metals)

76
Q

if a carbonate is present

A

fizzing due to CO2 will be observed

77
Q

testing for sulfate ions

A

BaCl2 solution acidified with hydrochloric acid is used as a reagent to
test for sulfate ions.

If acidified barium chloride is added to a solution that contains sulfate ions a
white precipitate of barium sulfate forms.

78
Q

removing a salt

A

filtration

79
Q

group 7 melting point

A

Increase down the group
As the molecules become larger they have
more electrons and so have larger van der
waals forces between the molecules. As the
intermolecular forces get larger more energy
has to be put into break the forces. This
increases the melting and boiling

80
Q

F- ions in H2SO4

A

White steamy fumes of HF are evolved

81
Q

Cl- ions in H2SO4

A

White steamy fumes of HCl are evolved.

82
Q

HBr in H2SO4

A

White steamy
fumes of HBr are evolved.
orange fumes of bromine are also
evolved and a colourless, acidic gas
SO2

83
Q

I- ions in H2SO4

A

White steamy fumes of HI are evolved.
Black solid and purple fumes of Iodine are
also evolved
A colourless, acidic gas SO2
A yellow solid of sulfur
H2S (Hydrogen sulfide), a gas with a bad egg
smell,

84
Q

chlorine in cleaning treatments

A

Chlorine is used in water treatment to kill bacteria. It has been used to treat drinking water and the water in
swimming pools. The benefits to health of water treatment by chlorine outweigh its toxic effects.

85
Q

Chlorine with water:
Cl2(g) + H2O (l) ⇌ HClO (aq) + HCl

A

If some universal indicator is added to the solution it will
first turn red due to the acidity of both reaction products. It
will then turn colourless as the HClO bleaches the colour.

86
Q

give the formula of a group 2 hydroxide used in agriculture

A

Ca(OH)2

87
Q

identify a sodium halide that does not undergo a redox reaction when added as a solid to concentrated sulfuric acid

A

NaF

88
Q

Cl2 + NaOH –>

A

NaCl + NaClO + H2

89
Q

lime water

A

cloudy precipitate formedt

90
Q

test for sulfate ions

A

-few drops of dilute HCl to sample
-add few drops of acidified barium chloride
-white precipitate formed

91
Q

test for ammonia

A

warm solution with NaOH
add damp red litmus paper which turns blue

92
Q

true or false - bromine dissolves in dilute ammonia

A

false - only concentrated

93
Q

explain what is observed when sodium chlorate was added to a colurless solution of potassium iodide

A

goes brown bc of iodine
iodine is oxidised

94
Q

how to distinguish between aqueous solutions of potassium nitrate and potassium sulfate

A

BaCl2

Nitrate = colourless solution

sulfate = white solid

95
Q

how to distinguish between MgCl2 and AlCl2

A

NaOH

Mg = white solid

Al = white solid that dissolves in exess

96
Q

bromine displaced (orange)

A

Cl2 + 2Br –> 2Cl- + Br2

97
Q

iodine displaced (brown)

A

Cl2 + 2I- —> 2Cl- + I2

Br2 + 2I- –> 2Br- + I2

98
Q

chlorine + NaOH

A

sodium chlorate

2NaOH + Cl2 –> NaClO + H2O + NaCl

99
Q

oxidising power (reducing agents)

A

decreases down group 7
more sheilding etc

100
Q

halide ions + concentrated sulfuric acid

sulfur = reduced
halide = oxidised

A

Sodium halides with H2SO4 = NaHSO4 = white misty fumes

form SO2 = Br = orange vapour and for I = yellow sulfur solid

Iodine = H2S = rotten egg smell

101
Q

identify the group 2 metal ion present in solution y and the ionic equation when it reacts with sulfuric acid

A

Ba2+ (sulfates less soluble down group)

SO4^2- + Ba2+ —> BaSO4

102
Q

identify the negative ion and the ionic equaton when magnesium nitrate is added to solution y

A

-OH- (hydroxides more soluble down the group so form white precipitate)

Mg2+ + 2OH- –> Mg(OH)2

103
Q

calculate the mass of potassium iodide needed to react with ClO- ions and observation

A

72.4mg

black solid appears

104
Q

state what reagent should be added to test between NaCl and BaCl2

A

H2SO4

NaCl = no reaction
BaCl2 = white ppt

105
Q

state what reagent should be added to test between NaCl and Na2CO3

A

acidified silver nitrate

NaCl = white ppt
Na2CO3 = effervescne/fizzing

106
Q

role of water in the reaction with calcium

A

oxidising agent

107
Q

reaction of calcium with excess water

A

Ca + 2H2O –> Ca + 2OH- + H2

108
Q

chlorine

A

Chlorine can be used to clean water and make it drinkable
The reaction of chlorine in water is a disproportionation reaction in which the chlorine gets both oxidised and reduced
This reaction is important in the purification of water for drinking and swimming pools

Chloric(I) acid (HClO) sterilises water by killing bacteria
Chloric acid can further dissociate in water to form ClO- (aq):
HClO (aq) → H+ (aq) + ClO- (aq)

ClO- (aq) also acts as a sterilising agent cleaning the water

109
Q

magnesium and TiCl4

A

Equation: 2Mg + TiCl4 → Ti + 2MgCl2
Role: Reducing agent

110
Q

State what is observed when aqueous chlorine is added to sodium bromide
solution.

A

yellow solution

Cl2 + 2 Br – → 2 Cl – + Br2

111
Q

State, in terms of redox, what happens to chlorine in the reaction in part
(c).

A

is oxidised and reduced (disporortionation reaction)

112
Q

Which statement is correct about the reaction between concentrated sulfuric acid
and solid sodium bromide?

A

oxidisng agent

Aqa a level chemistry (18 decks)

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