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Chemistry > 2.2 group 2 and group 7 > Flashcards

2.2 group 2 and group 7 Flashcards

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1
Q

what happens to atomic radius down group 2?

A

gets larger
extra electron shells are added

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2
Q

what happens to first ionisation energy down group 2?

A

decreases down the group
as atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so outer electrons are easier to remove

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3
Q

what happens to reactivity down group 2?

A

increases
as atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so outer electrons are easier to lose

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4
Q

what happens to melting point down group 2?

A

decreases
same charge on metal ions and same no of delocalised electrons
but atomic radius and electron shielding increase
so nuclear attraction for delocalised electrons decreases
so less energy needed to overcome strong metallic bonds

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5
Q

what happens to electronegativity down group 2?

A

decreases
atomic radius increases
electron shielding increases
so nuclear attraction for outer electrons decreases
so ability to attract pair of electrons in a covalent bond decreases

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6
Q

reaction of group 2 metals with water

A

oxidised from state of 0 to +2
metal + water -> metal hydroxide + hydrogen
react more readily down group as ionisation energy decreases

(but mg and steam makes metal oxide and h)

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7
Q

solubility of group 2 compounds

A

metal hydroxide (OH-) - more soluble down group

metal sulfate (SO4^2-) - less soluble down group

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8
Q

test for sulphate ions

A

add dilute HCl then barium chloride and presence of sulphate ions causes white precipitate of barium sulphate to form
(barium sulphate is insoluble)

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9
Q

use of barium sulphate because its insoluble. why is it good that its insoluble?

A

barium meal
swallowed by patient and it coats tissues in oesophagus/ stomach/ intestine so they show up on x-ray
other barium compounds cant be used as theyre soluble. barium sulphate isnt so cant be absorbed by cells so isnt harmful

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10
Q

use of magnesium

A

extracting titanium from its ore
titanium oxide is converted to titanium chloride by heating with carbon in steam of chlorine gas.
TiO2+ 2C + 2Cl2 -> TiCl4 + 2CO
titanium chloride then purified by fractional distillation then reduced by magnesium in furnace
TiCl4 (aq) + 2Mg (l) -> Ti (s) + 2MgCl2 (l)

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11
Q

removing sulfur dioxide from flue gases

A

mix calcium oxide or calcium carbonate with water to make an alkaline slurry
this is sprayed on flue gases and reaction occurs producing solid calcium sulfite

CaO(s)+2H20(l) +S02(g) ->CaSO3(s) +2H20(l)

CaCO3(s)+2H2O(l)+SO2(g)-> CaSO3(s)+2H2O (l)+C02(g)

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12
Q

What are group 2 metals used for as they are alkali?

A

neutralising acids
calcium hydroxide used in agriculture to neutralise acidic soils
magnesium hydroxide is used in indigestion tablets as an antacid

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13
Q

fluorine, chlorine, bromine and iodine colour, state, reactivity and uses?

A

Fl2- pale yellow gas, making plastics
Cl2- green gas, bleach and disinfectant
Br2- red brown liquid, testing saturation and water purification
I2- grey solid, antiseptic, mineral suppliment
all very reactive

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14
Q

what happens to boiling point down group 7?

A

increases
increased atomic radius, increased van der waals between molecules, more energy to break IMF

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15
Q

what happens to electronegativity down group 7?

A

decreases
atomic radius increases, more inner electron shielding, weaker attraction between nucleus and pair of electrons in a covalent bond

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16
Q

what happens to 1st ionisation energy down group 7?

A

decreases
increased atomic radius
more inner electron shielding
so weaker attraction from nucleus to electrons in outer shell

17
Q

are halide ions oxidising or reducing agents? what happens to this down the group?

A

reducing (they have gained an electron to become ions so are losing electrons when reducing)
more reducing down group as atoms get larger and outer shell further from nucleus so easier to lose electrons

18
Q

displacement reactions for group 7- draw the table

A

page 158 of text book

19
Q

MAKE FLASHCARDS FOR PAGE 159

A

Just read it

20
Q

how do you make bleach?

A

mix chlorine gas with cold, dilute sodium hydroxide at room temp and you get sodium chlorate (1)
2NaOH(aq) + Cl2(g) -> NaClO(aq) + NaCl(aq) +H2O(l)

21
Q

what is a disproportionation reaction?
eg?

A

one element is both oxidised and reduced
when making bleach, chlorine is oxidised and reduced

22
Q

reaction of chlorine and water

A

disproportionation and you get chloride and chlorate (1) ions
Cl2(g) +H2o (l) <->2H+(aq) + Cl-(aq) + ClO- (aq)

normal eq: Cl2(g) + H2O(l) <-> HCl(aq) + HClO(aq)

23
Q

reaction of chlorine and water under uv light

A

Cl2(g) +H2O(l) <-> 2H+(aq) + 2Cl- (aq) + 1/2 O2(g)

No chlorate ions produced so not effective at killing bacteria

24
Q

why can we use chlorine to treat water?

A

chlorate (1) ions produced when react with water and this kills bacteria so its safe to drink/ swim
but
chlorine is toxic

25
Q

benefits of using chlorine to treat water

A

kills disease causing microorganisms (and some chlorine stays in water preventing reinfection further down supply)
prevents growth of algae
eliminates bad taste and smells
removes discolouration caused by organic compounds

26
Q

limitations of using chlorine to treat water
what is the big BUT?

A

chlorine gas harmful if breathed in- irritates resp system
liquid chlorine on skin or in eyes can cause severe chemical burns
chlorine reacts with variety of organic compounds in water to form chlorinated hydrocarbons which can be carcinogenic
BUT
risks of untreated water (eg cholera epidemic) are worse than risks of chlorine

27
Q

are halogens oxidising or reducing agents? what happens to this down the group?

A

oxidising agents (they gain an electron)
decreases down the group as atomic radius gets larger so more shielding so less nuclear attraction for outer electrons

28
Q

reaction of halides with concentrated sulfuric acid

A

hydrogen halide produced then what happens next depends on halide- some strong enough reducing agents that they reduce sulfuric acid to sulfur dioxide and water. iodine is such a strong reducing agent it can reduce sulfur dioxide to H2S or S

29
Q

general equations and half equations for reaction of halides with concentrated sulfuric acid

A

NaX + H2SO4 -> NaHSO4 + HX
2HX + H2SO4 -> X2 + SO2 + 2H2O

2X- (g) -> X2(s) + 2e- (halide oxidised)
H2SO4 + 2H+ + 2e- -> SO2 + 2H2O (sulfuric acid reduced)

30
Q

What are the equations and observations of the reactions of halide ions with concentrated sulfuric acid?

A

On a separate poster (make sure to look)

31
Q

how do you test for halides?

A

add dilute nitric acid (not hcl due to chloride ions) to remove any ions which could interfere with the test
add few drops of silver nitrate solution (AgNO3(aq)) and a precipitate of silver halide will form
Ag+(aq) + X-(aq) -> AgX(s)

32
Q

what colour are the precipitates that form in the halide test? how can we further distinguish them?

A

fluoride- no precipitate (silver fluoride soluble)
chloride- white
bromide- cream
iodide- yellow

add ammonia as they all have diff solubilities
cl- dissolves in dilute NH3
br- dissolves in conc NH3
I- insoluble in NH3

33
Q

how do you test for group 2 ions?
2 ways

A

1) flame test- dip wire loop in conc hcl to clean then into compound then hold in flame Ca2+ brick red, Sr2+ red, Ba2+ pale green

2) add dilute NaOH dropwise and observe precipitate keep adding in excess and record changes

34
Q

precipitates formed from group 2 ions with NaOH then excess NaOH

A

Mg2+ slight white then white
Ca2+ slight white then slight white
Sr2+ slight white then slight white
Ba2+ no change then no change

35
Q

test for ammonium ions
equation of ammonium to ammonia gas

A

ammonia gas is alkaline so test with damp(so gas dissolves) red litmus paper and it goes blue
add hydroxide ions to solution containing ammonium ions, ammonia gas produced
NH4+(aq) + OH-(aq) -> NH3(g) + H2O(l)
so can add dilute sodium hydroxide solution to sample and gently heat then test with damp red litmus paper

36
Q

what is the test for sulfate ions? equation?

A

dilute HCl (get rid of carbonate and sulfate ions what would confuse the results and cant use sulfuric acid because of sulfate ions)
the barium chloride and white precipitate of barium sulfate forms
Ba^2+(aq) + SO4^2-(aq) -> BaSO4(s)

37
Q

what is the test for hydroxide ions?

A

they make a solution alkaline so use pH indicator eg red litmus paper goes blue

38
Q

what is the test for carbonate ions?
equation of carbonate ions and hydrogen

A

add dilute HCl and it will fizz as carbonate ions react w H ions in acid to give CO2
CO3^2-(aq) + 2H+(aq) -> CO2(g) + H2O(l)
test for CO2 by bubbling gas through limewater and it will go cloudy

Chemistry (16 decks)

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