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Inorganic Chemistry > 8.1 Group 2, 8.2 The Halogens & 8.3 Qualitative Analysis > Flashcards

8.1 Group 2, 8.2 The Halogens & 8.3 Qualitative Analysis Flashcards

1
Q

What is the reactivity trend as you down group 2, and why?

A
  • Reactivity increases down the group
  • The first and second ionisation energies decrease down the group
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2
Q

How do group 2 metals react with water? How does this change as you go down the group?

A
  • They form a hydroxide and hydrogen, and dissolve
  • The reaction becomes increasingly vigorous as you go down the group
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3
Q

How do group 2 metals react with dilute acid? How does this change as you go down the group?

A
  • They form a salt and hydrogen
  • The reaction becomes more vigorous as you go down the group
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4
Q

What happens when group 2 oxides react with water?

A
  • An alkaline solution of the metal hydroxide is formed, and hydroxide ions are released
  • MO(s) + H2O(l) -> M^2+(aq) + 2OH^-(aq)
  • When the solution becomes saturated, they start to form a precipitate
  • M^2+(aq) + 2OH^-(aq) -> M(OH)2(s)
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5
Q

What trends are there in there in solubility as you go down group 2?

A
  • It increases (more hydroxide ions are released)
  • Alkalinity increases
  • pH increases
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6
Q

What are 2 uses of group 2 metals? Give examples.

A
  • Calcium hydroxide is used to neutralise acidic soil
  • Magnesium hydroxide and calcium carbonate treat indigestion as they are used as antacids (they neutralise stomach acid)
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7
Q

What is the trend with boiling points in group 7? Explain it.

A
  • They increase down the group
  • This is because there are more electrons, so there are more London forces, and so more energy is required to overcome them
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8
Q

How does reactivity change down group 7, and how can you tell?

A
  • Reactivity decreases down the group
  • You can tell through displacement reactions; if a halogen displaces a halide, the solution changes colour to the colour of the displaced halogen; the halogen (not the halide) colours the solution
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9
Q

What colours do halogens turn in water?

A
  • Chlorine: pale green
  • Bromine: orange
  • Iodine: brown
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10
Q

How are the colours of halogens in solutions be told apart more easily?

A
  • In water, bromine is orange and iodine is brown, which can be difficult to tell apart
  • Cyclohexane can therefore be added as since it’s a non-polar organic solvent, the halogens dissolve more readily in it
  • In cyclohexane, iodine is violet while chlorine and bromine remain the same colour
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11
Q

Why does reactivity decrease down group 7?

A
  • The atomic radius increases
  • Electron shielding increases
  • Less nuclear attraction
  • As it becomes harder to form a 1- ion, reactivity decreases
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12
Q

What is disproportionation? Required.

A
  • A redox reaction in which the same element is both oxidised and reduced simultaneously
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13
Q

What are 2 reactions where disproportionation occurs?

A
  • The reaction of chlorine with water
  • The reaction of chlorine with cold, dilute sodium hydroxide
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14
Q

What is the equation for the reaction of chlorine and water?

A
  • Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)
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15
Q

What is the reaction of chlorine with water useful for?

A
  • The purification of water
  • This is done by chloric (I) acid (HClO) and chlorate (I) ions (ClO-) as they kill bacteria
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16
Q

What is the equation for the reaction of chlorine and cold, dilute sodium hydroxide?

A
  • Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
17
Q

What is the reaction of chlorine with sodium hydroxide useful for?

A
  • Making bleach
18
Q

What is the benefit of the use of chlorine in water treatment?

A
  • It kills bacteria
19
Q

What are the risks of using chlorine in water treatment?

A
  • Chlorine gas is toxic
  • It can form chlorinated hydrocarbons, which may cause cancer
20
Q

What is the difference between qualitative and quantitative analysis?

A
  • Qualitative analysis relies on simple observations
  • Quantitative analysis yields numerical results
21
Q

How are carbonate ions tested for?

A
  • They are reacted with H+ ions to form carbon dioxide
  • This is done by reacting a carbonate with an acid (usually nitric)
  • Bubble the gas produced through limewater, which will cause it to turn cloudy (carbon dioxide reacts with calcium hydroxide to form water and calcium carbonate, which is a white precipitate)
22
Q

How are sulfate ions tested for?

A
  • When they react with Ba2+, they form a white precipitate
  • Barium ions are usually added as barium nitrate
  • Most sulfates are soluble in water, but barium sulfate is very insoluble
23
Q

How are halides tested for?

A
  • Halides react with silver ions to form precipitates
  • Silver nitrate is added to a solution containing halides
  • Chloride, bromide and iodide ions form white, cream and yellow precipitates
  • You then use aqueous ammonia to tell them further apart (as the colours can look similar); chloride ions are soluble in dilute ammonia, bromide ions are soluble in concentrated ammonia, and iodide ions are insoluble in ammonia
24
Q

What is the correct order to test for anions in, and why?

A
  • Carbonate, sulfate and halide
  • Only carbonates form gas when reacted with acid, so since there is no possibility of a false result, this one goes first
  • Barium carbonate is also a white precipitate, so you have to do the carbonate test first and ensure there is no carbonate present
  • Silver carbonate and silver sulfate are both precipitates, so the halide test must be carried out last
25
Q

How do you test a mixture of anions?

A
  • You use nitric acid (so you’re not adding sulfate or chloride ions) in the carbonate test, and keep adding it until all of the bubbling stops
  • In the sulfate test, add an excess of barium nitrate (don’t use barium chloride), then filter the solid out
26
Q

How do you test for ammonium?

A
  • You react it with aqueous sodium hydroxide and heat the mixture, which releases ammonia gas
  • You can test for ammonia with damp pH indicator paper, which turns blue in its presence
  • NH4+ + OH- -> NH3 + H2O

Inorganic Chemistry (12 decks)

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