Topic 8: Group 2 and Group 7 Flashcards
1
Q
State one observation when magnesium reacts with steam
A
White solid forms
Mg (s) + H2O (g) –> MgO (s) + H2 (g)
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
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
4
Q
what happens to hydroxides and sulfates down group 2
A
hydroxides are more soluble
sulfates are less soluble down group 2
5
Q
what is the correct observation when barium metal is added to an excess of water
A
forms a colourless solution and effervesces
6
Q
which compound is used to treat symptoms of indigestion
A
Mg(OH)2
7
Q
equation for stronium with cold water
A
Sr (s) + 2H2O (l) –> Sr(OH)2 (aq) + H2 (g)
aqueous formed as more soluble
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
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
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)
11
Q
what happens to reactivity down group 2
A
increases
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)
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)
14
Q
why does beryllium not react with water
A
Beryllium doesn’t react with water as it has an insoluble surface oxide layer
15
Q
reactions of Mg,Ca,Sr
A
reacts with oxygen to form metal oxide MgO
16
Q
Ba reacts with excess oxygen to form what
A
Ba reacts with excess oxygen to form BaO2
17
Q
group 2 metals react with chlorine to form
A
-all group 2 metals react with chlorine to form XCl2 e.g BaCl2
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
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
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)
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)
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
23
Q
soluble vs insoluble hydroxides
A
Ba and Sr = soluble (aq)
Mg and Be = insoluble (s)
24
Q
soluble vs insoluble sulfates
A
Be and Mg = soluble
Ba and Sr = insoluble
25
barium sulfates
-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.
26
uses of group 2 metals
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
27
Explain why iodine forms essentially covalent compounds with metals
-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
28
Explain why flourine forms ionic compounds with hydrogen
-flourine is very electronegative which means covalent bond is so polarised that electrons are essentially fully transferred
29
true or false - group 7 elements are diatomic
true
30
what happens to reactivity as you go down the group 7
decreases as it becomes harder to add an electron
31
colours of bromine, chlorine and iodine
Chlorine = green-yellow gas
-Bromine = dark red liquid
-Iodine = dark grey solid
32
group 7
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
33
why does the boiling point of halogens increase down group 7
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
34
cl-cl bond
Cl-Cl = same electronegativity so is non-polar
Halogens = anions
35
Group 7 halogens colour in aqueous and vapor
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
36
halogens dissolve freely in hydrocarbon solvents
Halogens dissolve freely in hydrocarbon solvents such as cyclohexane and they produce the colours of their vapours e.g iodine = purple
37
why does flourine attract the most electrons
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.
38
why are halogen bonds essentially covalent
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.
39
displacement reaction
-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
40
displacement observations
Displacement observations (colour of halogen released)
-Chlorine = pale green
-Bromine = orange
-Iodine = brown
41
testing for halides
-halides = negative anions
-Halides are colourless ions which we can test for by adding aqueous silver nitrate solution (AgNO3)
42
halide precipitate colours
-Chloride = white precipitate
-Bromide = cream precipitate
-Iodide = yellow precipitate
43
steps of halide test
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
44
distinguish between precipitates
-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
45
Describe a further test to show whether solution C contains chloride or bromide ions
-add dilute ammonia solution
-if precipitate dissolves chloride ions are present
-not dissolve = bromide ions
46
what type of gas is formed and how to test for it
CO2
when bubbled through lime water a white precipitate is formed
47
explain how the observations from test 1 and 2 can be used to show that solution B has HCL
-effervescence = H+ ions
-white precipitate of silver chloride due to adding aqueous silver nitrate so contains chloride ions
48
describe a series of tests that the student can use to show that solution C contains ammonia sulfate
-warm solution with some NaOh
-damp red litmus turns blue
-add acidified BaCl2
-white precipitate formed
49
suggest the identity of the positive ion in solution A
Give the simplest ionic equation
Ba2+
Ba2+ + SO42- --> BaSO4
50
what gas turned litmus paper blue from red
ammonia
51
what property increases down group 7
boiling point
52
state what is observed when silver nitrate solution is added to sodium flouride solution
no precipitate formed
53
what colour precipitate is formed by oxides
white
54
what are group 2 oxides and hydroxides
bases
55
why is group 7 less reactive as you go down
harder to gain an electron and form an ion (weaker attraction)
56
state why magnesium hydroxide solution should not be used in titration of weak acids
-Mg(OH)2 = insoluble
57
why should water not be used to put out a fire in which magnesium metal is burning
-hydrogen is produced when group 2 metal put in water
-hydrogen is flammable
58
metal carbonate + acid
carbon dioxide + water + salt
59
what does effervescence in an acidic solution mean
presence of H+ ions
60
Describe a series of tests that the student can use to show that solution C contains ammonium sulfate
-warm with some NaOH
-damp red litmus at mouth of tube turns blue
-add acidified BaCl2
-white precipitate formed
61
Explain how the masses recorded during this experiment can be used to show that solution D contains a mixture of halide ions
-the 2nd mass is smaller --> mass after step 4 smaller than mass after step 2
-AgCl dissolves in dilute ammonia
62
reactions with sodium halides
-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
Cl- (halide)
HCl (products) --> steamy fumes
64
Br-
HBr --> steamy fumes
Br2 --> brown fumes
SO2 --> colourless gas
65
I-
Hi --> steamy fumes
I2 --> purple fumes
SO2 -> colourless gas
S --> yellow solid
H2S --> gas (bad egg smell)
66
H2SO4
Concentrated sulfuric acid can react as both an acid and an oxidising agent
67
formation of hydrogen halides
NaX + H2SO4 --> NaHSO4 + HX
68
explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution in this test for iodide ions
HCl would form a white precipitate
69
write an equation for the reaction of chlorine with cold water
Cl2 + H2O --> HClO + HCl
70
oxidising power down group 7
(oxidising agent)
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
chlorine + water
chlorine with water to form chloride ions and chlorate(I) ions.
72
group 2 melting point
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
magnesium with steam vs warm water
steam = produces MgO + H2
warm water = produces (MgOH)2 + H2
74
group 2 with cold water
Ca, Sr, Ba
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
observations when group 2 reacts with cold water
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
if a carbonate is present
fizzing due to CO2 will be observed
77
testing for sulfate ions
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
removing a salt
filtration
79
group 7 melting point
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
F- ions in H2SO4
White steamy fumes of HF are evolved
81
Cl- ions in H2SO4
White steamy fumes of HCl are evolved.
82
HBr in H2SO4
White steamy
fumes of HBr are evolved.
orange fumes of bromine are also
evolved and a colourless, acidic gas
SO2
83
I- ions in H2SO4
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
chlorine in cleaning treatments
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
Chlorine with water:
Cl2(g) + H2O (l) ⇌ HClO (aq) + HCl
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
give the formula of a group 2 hydroxide used in agriculture
Ca(OH)2
87
identify a sodium halide that does not undergo a redox reaction when added as a solid to concentrated sulfuric acid
NaF
88
Cl2 + NaOH -->
NaCl + NaClO + H2
89
lime water
cloudy precipitate formedt
90
test for sulfate ions
-few drops of dilute HCl to sample
-add few drops of acidified barium chloride
-white precipitate formed
91
test for ammonia
warm solution with NaOH
add damp red litmus paper which turns blue
92
true or false - bromine dissolves in dilute ammonia
false - only concentrated
93
explain what is observed when sodium chlorate was added to a colurless solution of potassium iodide
goes brown bc of iodine
iodine is oxidised
94
how to distinguish between aqueous solutions of potassium nitrate and potassium sulfate
BaCl2
Nitrate = colourless solution
sulfate = white solid
95
how to distinguish between MgCl2 and AlCl2
NaOH
Mg = white solid
Al = white solid that dissolves in exess
96
bromine displaced (orange)
Cl2 + 2Br --> 2Cl- + Br2
97
iodine displaced (brown)
Cl2 + 2I- ---> 2Cl- + I2
Br2 + 2I- --> 2Br- + I2
98
chlorine + NaOH
sodium chlorate
2NaOH + Cl2 --> NaClO + H2O + NaCl
99
oxidising power (reducing agents)
decreases down group 7
more sheilding etc
100
halide ions + concentrated sulfuric acid
sulfur = reduced
halide = oxidised
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
identify the group 2 metal ion present in solution y and the ionic equation when it reacts with sulfuric acid
Ba2+ (sulfates less soluble down group)
SO4^2- + Ba2+ ---> BaSO4
102
identify the negative ion and the ionic equaton when magnesium nitrate is added to solution y
-OH- (hydroxides more soluble down the group so form white precipitate)
Mg2+ + 2OH- --> Mg(OH)2
103
calculate the mass of potassium iodide needed to react with ClO- ions and observation
72.4mg
black solid appears
104
state what reagent should be added to test between NaCl and BaCl2
H2SO4
NaCl = no reaction
BaCl2 = white ppt
105
state what reagent should be added to test between NaCl and Na2CO3
acidified silver nitrate
NaCl = white ppt
Na2CO3 = effervescne/fizzing
106
role of water in the reaction with calcium
oxidising agent
107
reaction of calcium with excess water
Ca + 2H2O --> Ca + 2OH- + H2
108
chlorine
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
magnesium and TiCl4
Equation: 2Mg + TiCl4 → Ti + 2MgCl2
Role: Reducing agent
110
State what is observed when aqueous chlorine is added to sodium bromide
solution.
yellow solution
Cl2 + 2 Br – → 2 Cl – + Br2
111
State, in terms of redox, what happens to chlorine in the reaction in part
(c).
is oxidised and reduced (disporortionation reaction)
112
Which statement is correct about the reaction between concentrated sulfuric acid
and solid sodium bromide?
oxidisng agent
113
Give the reaction that takes place between chlorine and water in bright sunlight.
2Cl2 (aq) + 2H2O (l) --> 4HCl (aq) + O2 (aq)
114
Br- ions bigger than Cl- ions
Br- ions more easily oxidised = loose an electron quicker
115
ionic equation for chlorine and NaOH
Cl2 + 2OH- --> Cl- + ClO- + H2O
Cl- = -1
ClO- = +1
116
equation to show how chlorine forms an acidic solution in water
Cl2 + H2O --> HCl + HClO
(make sure arrow is reversible)
117
role of chlorine ions in the reaction with sodium
base (proton acceptor to form HCl
118
explain why the barium initially reacts more quickly than the magenisum
explain why the reaction stops before all the barium has reacted
-Ba is more reactive than Mg as outer electron shell is further away from the nucelus
-Ba reacts with H2SO4 to form BaSO4 (s) that is insoluble
-BaSO4 prevents further reaction
119
give on reason why chlorine ions are not formed when potassium chloride reacts with sulfuric acid
chlorine ions cannot reduce sulfuric acid
120
oxidation product from KBr
Bromine
121
reduction product from H2SO4
SO2
122
equation for chlorine in sunlight
2Cl₂(g) + 2H₂O(l) → 4HCl(aq) + O₂(g)`
123
chlorine in swimming pools
only used in small amounts
124
uses of products of the reaction between Cl2 and NaOH
Bleach
sterilises/kills bacteria
125
AgF =
soluble
126
equation for AgI and sodium thiosulfate and uses
AgI + 2S2O3^2- --> [Ag(S2O3)2]3- + I-
use in photography
127
observation of ethanoyl chloride (CH3COCl) with aqueous silver nitrate
white ppt formed immediately
128
chloroethanoic acid (ClCH3COOH) + aqueous silver nitrate
white ppt formed slowly
129
Mg equations = oxygen and cold water
2Mg + O2 --> 2MgO
Mg + 2H2O --> Mg(OH)2 + H2
