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Inorganic chemistry > 2.3 Group 7 - Halogens > Flashcards

2.3 Group 7 - Halogens Flashcards

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1
Q

What is the trend in melting point down Group 7?

A

Increase down the group
As the molecules become larger they have more electrons and so have larger van der waals forces between the molecules. As the intermolecular forces get larger more energy has to be put into break the forces. This increases the melting and boiling points.

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2
Q

What is the trend in electronegativity down Group 7?

A

As one goes down the group the electronegativity of the elements decreases.

As one goes down the group the atomic radii increases due to the increasing number of shells. The nucleus is therefore less able to attract the bonding pair of electrons.

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3
Q

What is electronegativity?

A

Electronegativity is the relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself.

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4
Q

How do halogens displace each other?

A

A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds.

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5
Q

What happens to oxidising strength down Group 7?

A

The oxidising strength decreases down the group. Oxidising agents are electron acceptors.

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6
Q

What are oxidising agents?

A

Oxidising agents are electron acceptors.

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7
Q

What does the colour of the solution when halides and halogens react show?

A

The colour of the solution in the test tube shows which free halogen is present in the solution.

Chlorine =very pale green solution (often colourless),

Bromine = yellow solution

Iodine = brown solution

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8
Q

What is the observation for the reaction when Potassium Chloride reacts with chlorine?

A

Very pale green solution, no reaction

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9
Q

What is the observation for the reaction when Potassium bromide reacts with chlorine?

A

Yellow solution, Cl has displaced Br

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10
Q

What is the observation for the reaction when Potassium iodide reacts with chlorine?

A

Brown solution, Cl has displaced I

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11
Q

What is the observation for the reaction when Potassium Chloride reacts with Bromine?

A

Yellow solution, no reaction

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12
Q

What is the observation for the reaction when Potassium Bromide reacts with Bromine?

A

Yellow solution, no reaction

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13
Q

What is the observation for the reaction when Potassium iodide reacts with Bromine?

A

Brown Solution, Br has displaced I

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14
Q

What is the observation for the reaction when Potassium chloride reacts with iodine?

A

Brown solution, no reaction

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15
Q

What is the observation for the reaction when Potassium bromide reacts with iodine?

A

Brown solution, no reaction

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16
Q

What is the observation for the reaction when Potassium iodide reacts with iodine?

A

Brown Solution, no reaction

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17
Q

What is the reaction between halide ions and silver nitrate used to test for?

A

This reaction is used as a test to identify which halide ion is present. The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.

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18
Q

What is the role of nitric acid in the reaction of halide ions with silver nitrate?

A

The role of nitric acid is to react with any carbonates present to prevent the formation of the precipitate Ag2CO3. This would mask the desired observations

2 HNO3 + Na2CO3 —> 2 NaNO3 + H2O + CO2

19
Q

silver halide precipitates can be treated with ammonia solution to help differentiate between them. If Silver chloride dissolves in dilute ammonia to form a complex ion what is observed?

A

AgCl(s) + 2NH3(aq) —>[Ag(NH3)2]+ (aq) + Cl- (aq)

Colourless solution

20
Q

silver halide precipitates can be treated with ammonia solution to help differentiate between them. If Silver Bromide dissolves in conc ammonia to form a complex ion what is observed?

A

AgBr(s) + 2NH3(aq) —>[Ag(NH3)2]+ (aq) + Br - (aq)

Colourless solution

21
Q

silver halide precipitates can be treated with ammonia solution to help differentiate between them. If Silver Iodide reacts with what is observed?

A

Silver iodide does not react with ammonia – it is too insoluble.

22
Q

What does the reaction of solid halides with conc sulfuric acid show?

A

That the halides show increasing power as reducing agents as one goes down the group.

23
Q

Why is there differing reducing power of halides down the group?

A

A reducing agent donates electrons.
The reducing power of the halides increases down group 7 They have a greater tendency to donate electrons.
This is because as the ions get bigger it is easier for the outer electrons to be given away as the pull from the nucleus on them becomes smaller.

24
Q

How do F- and Cl- react with H2SO4?

A

F- and Cl- ions are not strong enough reducing agents to reduce the S in H2SO4. No redox reactions occur. Only acid-base reactions occur.

25
Q

What Observed when Fluoride reacts with sulfuric acid?

A

NaF(s) + H2SO4(l) —>NaHSO4(s) + HF(g)

Observations: White steamy fumes of HF are evolved.

26
Q

What is Observed when Chloride reacts with sulfuric acid?

A

NaCl(s) + H2SO4(l) —> NaHSO4(s) + HCl(g)

Observations: White steamy fumes of HCl are evolved.

27
Q

Why is the reaction between Fluoride/Chloride and sulfuric acid an acid – base reactions and notredoxreactions?

A

H2SO4 plays the role of an acid (proton donor).

28
Q

What is the Acid-Base step and Redox step, and overall equation for the reaction of Br- with H2SO4?

A

Acid- base step:
NaBr(s) + H2SO4(l) —> NaHSO4(s) + HBr(g)

Redox step:
2 H+ + 2 Br - + H2SO4 —> Br2(g) + SO2(g) + 2 H2O(l)

Overall equation: combining two steps above:
2NaBr + 3H2SO4 —> 2NaHSO4 + SO2 + Br2 + 2H2O

29
Q

What is Observed when Br reacts with H2SO4?

A

Observations: White steamy fumes of HBr are evolved.

orange fumes of bromine are also evolved and a colourless, acidic gas SO2

30
Q

What is the reducing product when Br- reacts with H2SO4?

A

sulfur dioxide

31
Q

What role does H2SO4 play in the reaction of Br- and H2SO4?

A

H2SO4 plays the role of acid in the first step producing HBr and then acts as an oxidising agent in the second redox step.

32
Q

What is the Strongest halide reducing agent?

A

I- ions are the strongest halide-reducing agents. They can reduce the sulfur from
+6 in H2SO4 to +4 in SO2 ,to 0i n S and -2 in H2S.

33
Q

What is Observed when Iodide reacts with H2SO4?

A

White steamy fumes of HI are evolved. Black solid and purple fumes of Iodine are also evolved
A colourless, acidic gas SO2
A yellow solid of sulfur
H2S (Hydrogen sulfide), a gas with a bad egg smell.

34
Q

What is the reducing products in the reaction between iodide and sulfuric acid?

A

Reduction products = sulfur dioxide, sulfur and hydrogen sulfide

35
Q

What role does H2SO4 play in the reaction of I- and H2SO4?

A

H2SO4 plays the role of acid in the first step producing HI and then acts as an oxidising agent in the three redox steps.

36
Q

What is disproportionation?

A

Disproportionation is the name for a reaction where an element simultaneously oxidises and reduces.

37
Q

What is the equation of the reaction with Chhloine and water?

A

Cl (g) + HO(l)⇌ HClO(aq) + HCl(aq)

Chlorine is both simultaneously reducing and oxidising

38
Q

What is the equation for the reaction with water in sunlight
If the chlorine is bubbled through water in the presence of bright sunlight?

A

2Cl2 + 2H2O —> 4H+ + 4Cl- + O2

39
Q

What is Observed when water reacts with chlorine in the presence of bright sunlight?

A

The greenish colour of chlorine water fades as the Cl2 reacts and a colourless gas (O2) is produced.

40
Q

If a universal indicator is added the solution produced by the reaction of chlorine and water what is observed?

A

It will first turn red due to the acidity of both reaction products. It will then turn colourless as the HClO bleaches the colour.

41
Q

What chemical is used in water treatment to kill bacteria?

A

Chlorine

42
Q

What is the use of chlorine?

A

It has been used to treat drinking water and the water in swimming pools. The benefits to health of water treatment by chlorine outweigh its toxic effects.

43
Q

What is Observed in the Reaction of chlorine with cold dilute NaOH solution?

A

Cl2,(and Br2, I2) in aqueous solutions will react with cold sodium hydroxide. The colour of the halogen solution will fade to colourless.

44
Q

What is the use of the mixture NaCl and NaClO?

A

The mixture of NaCl and NaClO is used as bleach and to disinfect/ kill bacteria.

Inorganic chemistry (3 decks)

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