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AS Chemistry > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

Why do the halogens exist as diatomic molecules?

A

Because they have a single covalent bond between them

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2
Q

Why does mean bond enthalpy decrease as you go down the group?

A

Increased atomic number so more electron shells so greater atomic radius so weaker attraction

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3
Q

Why does fluorine not follow the trend of mean bond enthalpy?

A

Electrons are so close together that the lone pairs repel

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4
Q

What’s the trend in colour down the group?

A

Colour gets darker

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5
Q

Explain the trend in atomic radius down the group?

A

Increases down the group bc more shells and more shielding

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6
Q

Explain the trend in reactivity down the group

A

Decreases as you go down bc greater atomic radius so weaker electron affinity bc weaker attraction

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7
Q

Explain the trend in boiling points as you go down the group

A

Increases as you go down the group because more electrons means greater induced dipole dipole interactions so stronger van der Waals forces so more energy needed to overcome the forces

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8
Q

What is electronegativity?

A

The ability of an atom to attract a bonding pair of electrons

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9
Q

Explain the trend in electronegativity

A

Decreases as you go down bc bigger atomic radius so bonding pair further away so attractive force of the nucleus is further away

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10
Q

What do you get when you react cold aqueous sodium hydroxide with chlorine?

A

Sodium chlorate, NaClO, sodium chloride, NaCl and water

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11
Q

Write out the symbol equation for cold aqueous sodium hydroxide and chlorine

A

NaCl + Cl2 —-> NaClO + NaCl + H2O

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12
Q

Write out the ionic equation for cold aqueous sodium hydroxide and chlorine

A

2OH- + Cl2 —> Cl- + ClO- + H2O

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13
Q

Why is the reaction with cold aqueous sodium hydroxide a redox reaction?

A

Because Cl in Cl2 is 0, in NaClO it’s oxidised to +1 and in NaCl it’s reduced to Cl-

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14
Q

What is sodium chlorate used for?

A

Bleach to kill bacteria

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15
Q

What does chlorine dissolve in water to form?

A

Hydrochloric acid or chloric acid HOCl

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16
Q

What is chloric acid used for?

A

Sterilise drinking water and swimming pool water to kill bacteria bc it’s safe in low conc

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17
Q

What do chlorine and water react in sunlight to form?

A

HCl and O2 because the chloric acid is reduced to hydrogen ions and chloride ions

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18
Q

What is oxidising ability?

A

The ability to cause an oxidation to occur

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19
Q

What is an oxidising agent?

A

Compounds which cause oxidation to occur while being reduced themselves

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20
Q

Explain the trend in oxidising ability of the halogens down the group?

A

Reduces down a group bc greater atomic radius and increased shielding so harder to gain electrons

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21
Q

How can you show the trend in oxidising ability?

A

Displacement reactions - elements with greater oxidising ability displace those with weaker oxidising ability. Greater OA get reduced while other is oxidised

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22
Q

Explain the trend in the reducing ability of the halide ions down the group

A

Reducing ability increases as you go down the group bc greater atomic radius and more shielding means that outer electrons feel less attraction and are lost more easily so another substance can be oxidised

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23
Q

What experiment can you conduct to show the trend in reducing ability of the halides?

A

Solid halides with concentrated sulfuric acid

24
Q

What does concentrated sulfuric acid and sodium fluoride react to form?

A

sodium hydrogen sulfate and hydrogen fluoride

25
Q

What is observed when concentrated sulfuric acid and sodium fluoride react?

A

Misty white fumes of HF

26
Q

Write an equation for concentrated sulfuric acid and sodium fluoride

A

NaF + H2SO4 —> NaHSO4 + HF

27
Q

Why is concentrated sulfuric acid and sodium fluoride not a redox reaction?

A

No change in the oxidation state because fluorine isn’t a strong reducing agent to reduce the sulfur

28
Q

What does concentrated sulfuric acid and sodium chloride react to form?

A

Sodium hydrogen sulfate and hydrogen chloride

29
Q

What is observed when concentrated sulfuric acid and sodium chloride react?

A

White fumes

30
Q

Write an equation for concentrated sulfuric acid and sodium chloride

A

H2SO4 + NaCl —-> NaHSO4 + HCl

31
Q

Why is the reaction between concentrated sulfuric acid and sodium chloride not a redox reaction?

A

Because chlorine isn’t a strong enough reducing agent to reduce the sulfur

32
Q

What does concentrated sulfuric acid and potassium bromide react to form?

A

potassium hydrogen sulfate, hydrogen bromise, sulfur dioxide, water and bromine

33
Q

Write the non-redox equation for sulfuric acid and potassium bromide

A

H2SO4 + KBr —> KHSO4 + HBr

34
Q

Write the redox equation for sulfuric acid and potassium bromide

A

2HBr + H2SO4 —-> SO2 + Br2 + 2H2O2

35
Q

What is the overall equation between sulfuric acid and potassium bromide?

A

3H2SO4 + 2KBr —> 2KHSO4 + SO2+ 2H2O + Br

36
Q

What is observed when sulfuric acid reacts with potassium bromide?

A

Red brown vapour from the bromine and misty white fumes from the HBr (?)

37
Q

Reactants of KI + H2SO4 and observations

A

KHSO4 + HI and white misty fumes

38
Q

Reactants of 2HI + H2SO4 and observations

A

I2 + SO2 + 2H2O purple vapour and black solid

39
Q

Reactants of 6HI + H2SO4 and observations

A

3I2 + S + 4H2O yellow solid and black solid

40
Q

Reactants of 8HI + H2SO4 and observations

A

4I2 + H2S + 4H2O yellow solid and vapour that smells like eggs

41
Q

Why do the redox reactions occur?

A

Because of the relative reducing powers of the halides in the hydrogen halides

42
Q

Explain what test you would carry out to identify halide ions

A

Acidified silver nitrate solution. Spatula of sample is dissolved first in nitric acid and then silver nitrate is added

43
Q

Why is nitric acid added to the sample first?

A

To remove ions that would react with the silver ions of the silver nitrate such as carbonate ions which would form a precipitate and interfere with the test

44
Q

Why can the silver nitrate solution test not be used for silver fluoride?

A

Because silver fluoride is soluble in water and does not form a precipitate

45
Q

What ppt does silver chloride form?

A

White

46
Q

What ppt does silver bromide form?

A

Cream

47
Q

What ppt does silver iodide form?

A

Yellow

48
Q

What furhter test can be carried out after the silver nitrate test?

A

Ammonia solution

49
Q

How can the presence of silver chloride be confirmed?

A

Add dilute and concentrated ammonia solution and if chloride is present it should redissolve to form a colourless solution

50
Q

How can the presence of silver bromide be confirmed?

A

Doesn’t redissolve in dilute ammonia solution but does redissolve in concentrated ammonia solution

51
Q

How can the presence of silver iodide be confirmed?

A

Doesn’t redissolve in concentrated and dilute ammonia solution

52
Q

Explain the experiment and observations of the test to test for sulfate ions

A

Acidified barium chloride solution. Add nitric acid to the solution first then add barium chloride. White precipitate means sulfate ions are present while no ppt means no sulfate ions

53
Q

Explain the experiment and observations of the test to test for carbonate ions/hydrogencarbonate ions

A

Dilute nitric acid added to sample - if effervescence is given off then CO2 is given off and carbonate ions are present

54
Q

Explain the experiment and observations of the test to test for just carbonate ions

A

Magnesium nitrate/chloride. Add deionised water then magnesium nitrate/chloride White ppt means carbonate ions are present

55
Q

Explain the experiment and observations of the test to test for magnesium and calcium ions

A

Sodium hydroxide solution. Add deionised water then a few drops of sodium hydroxide solution to form ppt. To see if ppt dissolves add excess sodium hydroxide. If precipitate forms then Mg and Ca ions present.

56
Q

Explain the experiment and observations of the test to test for ammonium ion (NH4+)

A

Sodium hydroxide solution. Add solution and test the gas with wet litmus paper. If it turns blue then ammonia is present bc ammonia gas is alkaline

AS Chemistry (14 decks)

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