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A-Level Chemistry > Chapter 8 - Reactivity Trends > Flashcards

Chapter 8 - Reactivity Trends Flashcards

1
Q

what are grp 2 metals known as

A

alkaline earth metals

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2
Q

electron config. of grp 2 metals

A
  • fill 2s-sub-shell
  • 2 electrons in outershell
  • reducing agents as loses electrons so oxidised
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3
Q

grp 2 metals reactions

A
  • oxygen —> makes metal oxide
  • water —> makes hydroxide and hydrogen
  • dilute acids —> makes salt and hydrogen
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4
Q

trend in grp 2 reactivity

A

increases as more shielding and atomic radius so less nuclear attraction

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5
Q

grp 2 metal oxides reactions

A

water –> releases hydroxide ions and metal ions
- when solution is saturated, any more metal and hydroxide ions will form solid precipitate

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6
Q

solubility of hydroxides

A
  • increases down the group, solutions contain more hydroxide ions and are more alkaline
  • pH and alkalinity increases
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7
Q

grp 2 compounds used in agriculture

A
  • Ca(OH)2 is added to fields as lime by farmers to increase pH of acidic soils
  • neutralises acid in water forming water
    Ca(OH)2 (s) + 2H+ (aq) –> Ca+2 (aq) + 2H2O (l)
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8
Q

grp 2 compounds used in medicine

A
  • grp 2 bases are used as antacids to treat acid indegestion
  • many tables use Calcium Carbonates/ magnesium hydroxide
  • ‘milk of magnesia’ is a suspension of white magnesium hydroxide
    Mg(OH)2 + 2HcCl —> MgCl2 + 2H2O
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9
Q

what are the halogens

A

grp 7 elements
exist as diatomic molecules at RTP

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10
Q

Flourine

A

pale yellow gas

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11
Q

Chlorine

A

pale green gas

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12
Q

Bromine

A

red-brown liquid

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13
Q

Iodine

A

shiny grey-black solid

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14
Q

b.p down grp 7

A
  • increases down the group, more electrons and London forces so more energy needed, so higher b.p
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15
Q

reactivity down the group

A
  • decreases, more shielding and radius so harder to attract electron
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16
Q

halogen-halide displacement reactions

A
  • if halogen added is more reactive then it displaces the halide ion
17
Q

Cl- + Br2
Cl- + I2
Br- + I2

A

no reaction

18
Q

Br- + Cl2
I- + Cl2
I- + Br2

A
  1. turns orange
  2. turns purple
  3. turns purple
19
Q

what do you add to displacement reaction

A

cyclohexane to tell colours apart - organic non-polar solvent
chlorine is pale green
bromine is orange
iodine is violet

20
Q

disproportionation

A

where same species is oxidised and reduced

21
Q

chlorine with water

A
  • used in water purification - kills bacteria
  • Cl2(aq) + H2 (l) —> HClO (aq) + HCl (aq)
  • bacteria killed by chlorate ions in chloric acid, HClO
  • also acts as a weak bleach
22
Q

chlorine reacts with cold, dilute aqueous NaOH

A
  • reaction of chlorine with water is limited by low solubility
  • if water has dissolved NaOH then more chlorine dissolves
    Cl2(aq) + 2NaOH (aq) –> NaClO (aq) + NaCl (aq) + H2O (l)
24
Q

Benefits & Risks of Chlorine

A
  • beneficial in ensuring water is drinkable
  • chlorine gas is toxic
  • chlorine in drinking water can react with organic hydrocarbons which could cause cancer
  • risk is smaller then not added chlorine to water
24
Q

Qualitative analysis

A

relies on simple observations not measurements

25
Q

Carbonate test

A
  • reacts with acids to form carbon dioxide (dilute nitric acid)
  • if bubbles form, bubble through lime water (calcium hydroxide) - turns cloudy
    CO2 (g) + Ca(OH)2 (aq) –> CaCO3 (s) + H2O (l)
26
Q

sulfate test

A

add barium nitrate, should form barium sulfate which is insoluble in water

26
Q

halide tests

A

add silver nitrate
chloride - white precipitate
bromine - cream precipitate
iodide - yellow precipitate

27
Q

how to test halides apart

A

add ammonia
chloride - redissolves in dilute ammonia
bromine - redissolves in conc. ammonia
iodide - doesn’t redissolve

28
Q

ammonium test

A
  • add aqueous NaOH
  • produces ammonia, hard to see bubbles as soluble in water
  • warm mixture and releases ammonia gas
  • use moist pH indicator paper - it’s alkaline - turns paper blue
29
Q

sequence of tests

A
  1. carbonate
  2. sulfate
  3. halide
30
Q

why does carbonate test have to be done first?

A
  • sulfates and halides don’t produce bubbles when reacting with dilute acid - carried out without possibility of incorrect conclusion
  • if present keep adding acid till bubbles stop to remove presence of ions
31
Q

why does sulfate test have to be done second?

A
  • barium carbonate is also a white precipitate
  • so carry out carbonate test before hand to make sure no carbonate ions are present and if precipitate forms it’s due to sulfate ions
  • can filter solution after to remove barium sulfate so can test for halides
32
Q

why does halide test have to be done third?

A
  • silver carbonate and silver sulfate are both insoluble and form precipitates
  • so carry out test last when possibility of carbonates and sulfates have been ruled out

A-Level Chemistry (15 decks)

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