Topic 8: Group 2 and Group 7 Flashcards
State one observation when magnesium reacts with steam
White solid forms
Mg (s) + H2O (g) –> MgO (s) + H2 (g)
what is the equation for when barium reacts with water and evidence for the formation of barium hydroxide
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
contrast these observations with those for calcium with water
-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
what happens to hydroxides and sulfates down group 2
hydroxides are more soluble
sulfates are less soluble down group 2
what is the correct observation when barium metal is added to an excess of water
forms a colourless solution and effervesces
which compound is used to treat symptoms of indigestion
Mg(OH)2
equation for stronium with cold water
Sr (s) + 2H2O (l) –> Sr(OH)2 (aq) + H2 (g)
aqueous formed as more soluble
describe what you would see if you dropped some pieces of calcium into cold water
-vigorous reaction producing a colourless gas
-calcium would disappear to leave a white precipitate in a colourless solution
what is the least reactive element in group 2 and why
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
reactions with water (1)
-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)
what happens to reactivity down group 2
increases
group 2 reactions with water (2)
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)
magnesium reacting with steam
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)
why does beryllium not react with water
Beryllium doesn’t react with water as it has an insoluble surface oxide layer
reactions of Mg,Ca,Sr
reacts with oxygen to form metal oxide MgO
Ba reacts with excess oxygen to form what
Ba reacts with excess oxygen to form BaO2
group 2 metals react with chlorine to form
-all group 2 metals react with chlorine to form XCl2 e.g BaCl2
Group 2 metals (not including Be) react with water to form
-Mg – Ba reacts with water to form a metal hydroxide with hydrogen e.g Mg(OH)2 + H2
group 2 oxides reacting with water
-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
what forms when group 2 oxides e.g MgO react with water
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)
hydroxides
-Hydroxides become more soluble as you go down the group to form alkaline solutions
-Solubility increases as alkalinity increase (more OH- ions)
calcium hydroxide
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
soluble vs insoluble hydroxides
Ba and Sr = soluble (aq)
Mg and Be = insoluble (s)
soluble vs insoluble sulfates
Be and Mg = soluble
Ba and Sr = insoluble
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.
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
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
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
true or false - group 7 elements are diatomic
true
what happens to reactivity as you go down the group 7
decreases as it becomes harder to add an electron
colours of bromine, chlorine and iodine
Chlorine = green-yellow gas
-Bromine = dark red liquid
-Iodine = dark grey solid
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
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
cl-cl bond
Cl-Cl = same electronegativity so is non-polar
Halogens = anions
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
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
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.
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.
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
displacement observations
Displacement observations (colour of halogen released)
-Chlorine = pale green
-Bromine = orange
-Iodine = brown
testing for halides
-halides = negative anions
-Halides are colourless ions which we can test for by adding aqueous silver nitrate solution (AgNO3)
halide precipitate colours
-Chloride = white precipitate
-Bromide = cream precipitate
-Iodide = yellow precipitate
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
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
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
what type of gas is formed and how to test for it
CO2
when bubbled through lime water a white precipitate is formed
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
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
suggest the identity of the positive ion in solution A
Give the simplest ionic equation
Ba2+
Ba2+ + SO42- –> BaSO4
what gas turned litmus paper blue from red
ammonia
what property increases down group 7
boiling point
state what is observed when silver nitrate solution is added to sodium flouride solution
no precipitate formed
what colour precipitate is formed by oxides
white
what are group 2 oxides and hydroxides
bases
why is group 7 less reactive as you go down
harder to gain an electron and form an ion (weaker attraction)
state why magnesium hydroxide solution should not be used in titration of weak acids
-Mg(OH)2 = insoluble
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
metal carbonate + acid
carbon dioxide + water + salt
what does effervescence in an acidic solution mean
presence of H+ ions
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
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
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
Cl- (halide)
HCl (products) –> steamy fumes
Br-
HBr –> steamy fumes
Br2 –> brown fumes
SO2 –> colourless gas
I-
Hi –> steamy fumes
I2 –> purple fumes
SO2 -> colourless gas
S –> yellow solid
H2S –> gas (bad egg smell)
H2SO4
Concentrated sulfuric acid can react as both an acid and an oxidising agent
formation of hydrogen halides
NaX + H2SO4 –> NaHSO4 + HX
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
write an equation for the reaction of chlorine with cold water
Cl2 + H2O –> HClO + HCl
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.
chlorine + water
chlorine with water to form chloride ions and chlorate(I) ions.
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
magnesium with steam vs warm water
steam = produces MgO + H2
warm water = produces (MgOH)2 + H2
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)
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)
if a carbonate is present
fizzing due to CO2 will be observed
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.
removing a salt
filtration
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
F- ions in H2SO4
White steamy fumes of HF are evolved
Cl- ions in H2SO4
White steamy fumes of HCl are evolved.
HBr in H2SO4
White steamy
fumes of HBr are evolved.
orange fumes of bromine are also
evolved and a colourless, acidic gas
SO2
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,
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.
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.
give the formula of a group 2 hydroxide used in agriculture
Ca(OH)2
identify a sodium halide that does not undergo a redox reaction when added as a solid to concentrated sulfuric acid
NaF
Cl2 + NaOH –>
NaCl + NaClO + H2
lime water
cloudy precipitate formedt
test for sulfate ions
-few drops of dilute HCl to sample
-add few drops of acidified barium chloride
-white precipitate formed
test for ammonia
warm solution with NaOH
add damp red litmus paper which turns blue
true or false - bromine dissolves in dilute ammonia
false - only concentrated
explain what is observed when sodium chlorate was added to a colurless solution of potassium iodide
goes brown bc of iodine
iodine is oxidised
how to distinguish between aqueous solutions of potassium nitrate and potassium sulfate
BaCl2
Nitrate = colourless solution
sulfate = white solid
how to distinguish between MgCl2 and AlCl2
NaOH
Mg = white solid
Al = white solid that dissolves in exess
bromine displaced (orange)
Cl2 + 2Br –> 2Cl- + Br2
iodine displaced (brown)
Cl2 + 2I- —> 2Cl- + I2
Br2 + 2I- –> 2Br- + I2
chlorine + NaOH
sodium chlorate
2NaOH + Cl2 –> NaClO + H2O + NaCl
oxidising power (reducing agents)
decreases down group 7
more sheilding etc
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
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
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
calculate the mass of potassium iodide needed to react with ClO- ions and observation
72.4mg
black solid appears
state what reagent should be added to test between NaCl and BaCl2
H2SO4
NaCl = no reaction
BaCl2 = white ppt
state what reagent should be added to test between NaCl and Na2CO3
acidified silver nitrate
NaCl = white ppt
Na2CO3 = effervescne/fizzing
role of water in the reaction with calcium
oxidising agent
reaction of calcium with excess water
Ca + 2H2O –> Ca + 2OH- + H2
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
magnesium and TiCl4
Equation: 2Mg + TiCl4 → Ti + 2MgCl2
Role: Reducing agent
State what is observed when aqueous chlorine is added to sodium bromide
solution.
yellow solution
Cl2 + 2 Br – → 2 Cl – + Br2
State, in terms of redox, what happens to chlorine in the reaction in part
(c).
is oxidised and reduced (disporortionation reaction)
Which statement is correct about the reaction between concentrated sulfuric acid
and solid sodium bromide?
oxidisng agent
Give the reaction that takes place between chlorine and water in bright sunlight.
2Cl2 (aq) + 2H2O (l) –> 4HCl (aq) + O2 (aq)
