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OCR A a-level chemistry > Module 3 - [ch8] (reactivity trends) > Flashcards

Module 3 - [ch8] (reactivity trends) Flashcards

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1
Q

what are the group 2 elements also known as

A

alkaline earth metals

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2
Q

what is the most common reaction of group2 elements

A

redox
loses its two outermost electrons and be reduced
acts as a reducing agent

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3
Q

group2 metal + oxygen

A

metal oxide

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4
Q

group2 metal + water

A

alkaline hydroxide + hydrogen
M(OH)2 + H2

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5
Q

how does reactivity of the group2 metals change going down the group

A

becomes more vigorous down the group

reactivity increases down the group

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6
Q

metal + acid

A

salt + hydrogen

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7
Q

why does reactivity increase down group 2

A

the atoms of group2 lose 2 electrons to form 2+ ions
ionisation energy decreases down the group
due to increases atomic radius, electron shielding
less energy needed for reaction to occur down the group

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8
Q

group2 oxide + water

A

release hydroxide ions (OH~)
only slightly soluble in water

when solution becomes saturated
Ca+(aq) + OH~(aq) -> Ca(OH)2(s)
solid precipitate formed

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9
Q

solubility of hydroxides in water

A

increases down the group
down group contain more OH~ (aq) ions and are more alkaline, pH increases

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10
Q

what are group 2 compounds often used as

A

bases

oxides
hydroxides
carbonates

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11
Q

group2 compound uses

A

Ca(OH)2
calcium hydroxide
agriculture - added to fields as lime to increase pH of acidic soils
neutralises acidic soil forming neutral water

Mg(OH)2
magnesium hydroxide
antacids to treat acid indigestion
CaCO3
calcium carbonate

+ HCl (stomach acid)

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12
Q

equation for antacid

A

CaCO3(s) + HCl(aq) -> CaCl(aq) + H2O(l) + C2O(g)

OR

Mg(OH)2(s) + 2HCl(aq) -> MgCl2(aq) + 2H2O(l)

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13
Q

trend in boiling points of halogens

A

increases down group
more electrons
stronger london forces
more energy required to break intermolecular forces

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14
Q

how do halogens exist

A

as diatomic molecules

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15
Q

most common type of reaction for halogens and why

A

redox
each halogen atom has 7 electrons on outer shell
only needs to gain one for stable noble gas configuration
each halogen atom reduced to form 1- halide ion
acts as an oxidising agent

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16
Q

what experiment can be carried to show how the reactivity of halogens decrease down a group

A

displacement reaction
oxidation
if the halogen is more reactive it displaces the halide in solution
colour change

    Cl2(aq)      Br2(aq)       I2(aq) Cl~        X            none          none Br~  orange          X              none I~     purple       purple           X
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17
Q

how can you tell apart Cl2, Br2 and I2

A

solution in water
Cl2 - pale green
Br2 - orange
I2 - brown

not very clear, hard to distinguish between orange and brown

+ organic non-polar solvent
cyclohexane
shake
non-polar halogens dissolve more readily in non-polar solvent
Cl2 - pale green
Br2 - orange
I2 - violet

18
Q

fluorine

A

pale yellow gas
extremely reactive

19
Q

astatine

A

extremely rare
radioactive and decays rapidly
never been seen
predicted to be the least reactive halogen

20
Q

reactivity of halogens

A

reactivity decreases down group
atomic radius increases
shielding increases
nuclear attraction decreases
more difficult to attract electron to outer shell

21
Q

what is disproportionation

A

redox reaction in which the same element is oxidised and reduced

22
Q

what is chlorine used in

A

water purification
chloric acid produced (HClO) kills bacteria
chloric acid(I) acid also acts as weak bleach

23
Q

what type of reaction is chlorine and water
give the equation

A

disproportionation
Cl2(aq) + H2O(l) -> HClO(aq) + HCl(aq)

24
Q

household beach
what is the equation

A

NaClO
Cl2(aq) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) H2O(l)

disproportionation

reaction between chlorine and water is limited by low solubility of chlorine in water
if water has sodium hydroxide much more chlorine dissolves

25
Q

benefits and risks of chlorine use

A

BENEFITS
kills bacteria so we can have safe to drink water

RISKS
chlorine is extremely toxic
respiratory irritant in small concentrations
large conc, fatal
may react with organic hydrocarbons in the water to form chlorinated hydrocarbons which are suspected of causing cancer

26
Q

carbonate test

A

bubble through lime water
if it goes cloudy
CO2 present

27
Q

what is limewater

A

saturated aqueous solution of calcium hydroxide Ca(OH)2

CO2 reacts with this to form fine white precipitate CaCO3 which turns limewater ‘cloudy’

28
Q

sulfate test

A

Add dilute hydrochloric acid and Ba 2+ (aq) ions to solution (barium chloride, not when testing a mixture tho)
they will react with sulfate ion SO4 2- to form BaSO4
solid white precipitate

29
Q

testing for halide ions

A

aqueous silver nitrate AgNO3 to an aqueous solution of a halide
Ag+ ions react with halide ions to form solid precipitates
Cl - white
Br - cream
I - yellow

30
Q

what test often accompanies the halide test with silver nitrate and why

A

test of solubility of the precipitate with aqueous ammonia
precipitate colours can be hard to distinguish between
Cl - fully soluble
Br - partially soluble
I - insoluble

31
Q

what is the sequence of tests

A

carbonate
sulfate
halides

32
Q

why is the carbonate test done first

A

you’re looking for a gas
neither halide nor sulfate produce bubbles with dilute acid, only carbonates
so bubbles definitely = carbonate

33
Q

how should you carry out a carbonate test on a mixture of ions

A

carry the carbonate test out first
if you see bubbles continue adding dilute nitric acid until the bubbling stops
so all carbonate ions have been removed

34
Q

why should dilute nitric acid be used in the carbonate test when testing a mixture of ions

A

sulfuric acid has sulfate ions which will show up in sulfate test
Hydrochloric acid has chloride ions which will also show up in halide test

35
Q

testing a mixture of ions

A

carbonate test
dilute nitric acid

sulfate test
excess Ba(NO3)2(aq)
filter

halide test
AgNO3(aq)
add NH3 to confirm precipitate

36
Q

why should an excess of Ba(NO3)2 (aq) be used

A

so all sulfate ions present will precipitate out as Barium sulfate

37
Q

how do you test for ammonium ion NH4+

A

add aqueous sodium hydroxide NaOH(aq)
ammonia gas produced (won’t see bubbles as it is soluble in water)
warm the mixture, ammonia gas released
test with moist pH indicator paper - blue paper (smell)

NH4+(aq) + OH~(aq) -> NH3(g) + H2O(l)

38
Q

which group2 element doesn’t react with water

A

berrylium

39
Q

magnesium + water

A

very slow reaction

40
Q

equation for carbonate ion test

A

CO3 2- + H+ -> CO2 + H2O

41
Q

equation for sulfate test

A

Ba2+ + SO4 2- -> BaSO4

42
Q

equation for ammonium test

A

NH4+(aq) + OH~ -> NH3(aq) + H2O(aq)

OCR A a-level chemistry (11 decks)

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