3.2.3 - Group 7, the Halogens

Question 1

What is the trend in m.p/b.p down group 7?

Answer 1

Increases down the group.

As the molecules become larger, they have more electrons and so have stronger VDW forces between the molecules. As the forces get larger, more energy has to be put in to break the forces.

Question 2

What are the colours of solution for each type of free halogen?

Answer 2

Chlorine = Pale Green (often colourless), Bromine = Yellow/Orange Solution, Iodine = Brown Solution.

Question 3

How do we test for various halide ions?

Answer 3

The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise.

Question 4

What is the role of H2SO4 in acid-base reactions?

Answer 4

Proton donor.

Question 5

What is a disproportionation reaction?

Answer 5

A reaction in which a species/element is both oxidised and reduced.

Question 6

What does Bromine form?

Answer 6

Brown-orange liquid.

Question 7

What happens to the Electronegativity as we go down the group?

Answer 7

Decreases as we go down the group, as the distance increases between the nucleus and atom; so increased shielding.

Question 8

What happens to the Reactivity as we go down the group?

Answer 8

Decreases as we go down the group. Atoms with a smaller radius have a stronger attraction. Halogens are less oxidizing as we go down the group.

Question 9

What do halogens do to halides?

Answer 9

Halogens displace a halide from the solution if the halide is lower in the periodic table.

Question 10

What is Bleach made from?

Answer 10

Made via a Disproportion reaction from chlorine and sodium hydroxide forming sodium chlorate.

Question 11

Purposes of bleach?

Answer 11

Treat water, Bleaching papers and fabrics, Cleaning agent.

Question 12

How does Sunlight decompose chlorinated water?

Answer 12

Sunlight decomposes chlorinated water.

Question 13

Explain how to further test after silver nitrate test for halide ions?

Answer 13

Add Dilute ammonia to each. Chloride ions dissolve with dilute ammonia. Concentrated ammonia causes silver Bromide to dissolve. Silver iodide doesn’t dissolve with concentrated ammonia as it’s insoluble.

Question 14

How do we test for ammonium compounds?

Answer 14

Add sodium Hydroxide to ammonium compound, gently heat. If ammonium is present, ammonia gas will be produced. Use Red litmus paper - will turn blue if ammonia gas is being produced.

Question 15

How do we test for Hydroxide ions?

Answer 15

Hydroxides are alkaline, so they turn red litmus paper blue.

Question 16

How do you test for carbonates?

Answer 16

HCL reacts with carbonates to make CO2 gas; when bubbled through limewater it turns cloudy.

Question 17

What does AgNO3 produce?

Answer 17

Produces white precipitates when reacting with chloride.

Question 18

Colours of the first 4 halogens?

Answer 18

Fluorine - Pale yellow gas, Chlorine - green gas, Bromine - Brick red solution, Iodine - Grey solid.

Question 19

How do you test for iodine?

Answer 19

Adding starch solution - where if blue-black colour iodine is present or Add AgNO3, where a yellow precipitate is formed.

Question 20

What is the strongest halide reducing agent?

Answer 20

Iodide.

Question 21

Trend of Reducing power down group 7?

Answer 21

Reducing power of halides increases as you go down group 7, where fluoride ions are the weakest reducing agent but strongest oxidizing agent.

Question 22

What are halogens, and list their common states at room temperature?

Answer 22

Halogens are elements found in Group 17 of the periodic table, known for being highly reactive. Common states at room temperature include: Fluorine (F2) as a very pale yellow gas, Chlorine (Cl2) as a greenish gas, Bromine (Br2) as a red liquid, and Iodine (I2) as a shiny grey solid that sublimes to purple gas.

Question 23

Describe the trend in melting and boiling points among the halogens.

Answer 23

The melting and boiling points of halogens increase down the group. This is due to the increase in molecular size and number of electrons, which enhances the van der Waals forces between the molecules, requiring more energy to break these intermolecular forces.

Question 24

Explain the trend in electronegativity observed among the halogens.

Answer 24

Electronegativity decreases down the group among halogens. As atomic radii increase due to more electron shells, the effective nuclear attraction on the bonding pair of electrons decreases, making the atoms less electronegative.

Question 25

What determines the ability of one halogen to displace another from a compound?

Answer 25

A halogen can displace another halogen from a compound if it is a stronger oxidizing agent. The oxidizing strength generally decreases down the group, hence a halogen higher in the group can displace those below it from their compounds.

Question 26

Explain what happens when chlorine water is added to potassium bromide solution.

Answer 26

When chlorine water is added to potassium bromide solution, chlorine acts as a strong oxidizing agent and displaces bromine, forming a yellow solution indicating the presence of bromine.

Question 27

Describe the outcomes of adding silver nitrate to different halide solutions.

Answer 27

Fluorides produce no precipitate; chlorides produce a white precipitate of AgCl; bromides yield a cream precipitate of AgBr; and iodides form a pale yellow precipitate of AgI. These precipitates can help identify the type of halide present.

Question 28

How can you differentiate between silver chloride and silver bromide using ammonia?

Answer 28

Silver chloride dissolves in dilute ammonia to form a colorless solution, indicating the formation of a complex ion, [Ag(NH3)2]+. Silver bromide requires concentrated ammonia to dissolve, also forming a colorless solution.

Question 29

Compare the reactivity of fluoride, chloride, and bromide ions with concentrated sulfuric acid.

Answer 29

Fluoride and chloride ions react with concentrated sulfuric acid in acid-base reactions, producing HF and HCl gases, respectively. Bromide ions undergo a redox reaction, producing bromine and sulfur dioxide gases.

Question 30

How does the reducing power of halide ions change down the group?

Answer 30

The reducing power of halide ions increases down the group. Iodide is the strongest reducing agent, able to reduce sulfur in sulfuric acid to various lower oxidation states including sulfur dioxide, sulfur, and hydrogen sulfide.

Question 31

Explain the trend in oxidizing strength among halogens.

Answer 31

The oxidising strength of halogens decreases down the group. Fluorine is the strongest oxidising agent, followed by chlorine, bromine, and iodine. This trend is due to decreasing electronegativity and increasing atomic size, which reduces the ability to attract additional electrons.

Question 32

What are the color changes observed in the displacement reactions of halogens with halide ions?

Answer 32

Chlorine displaces bromine and iodine from their salts, turning the solution from colorless to yellow (bromine) or brown (iodine). Bromine displaces iodine, turning the solution brown. The solutions indicate the presence of free halogens.

Question 33

Describe the procedure and results for testing halides with silver nitrate.

Answer 33

To test for halides, add silver nitrate solution to a sample treated with nitric acid. Fluoride ions give no precipitate; chloride ions give a white precipitate; bromide ions give a cream precipitate; iodide ions give a pale yellow precipitate.

Question 34

How do silver halide precipitates react with ammonia?

Answer 34

Silver chloride dissolves in dilute ammonia, forming a colorless solution. Silver bromide requires concentrated ammonia to dissolve, also yielding a colorless solution. Silver iodide does not dissolve in ammonia.

Question 35

What happens when different halide salts react with concentrated sulfuric acid?

Answer 35

Fluoride and chloride ions only show acid-base reactions, evolving HF and HCl gases, respectively. Bromide and iodide ions undergo redox reactions, producing bromine and iodine along with sulfur dioxide for bromide, and sulfur dioxide, sulfur, and hydrogen sulfide for iodide.

Question 36

Describe the disproportionation reaction of chlorine in water.

Answer 36

Chlorine reacts with water in a disproportionation reaction to form hydrochloric acid (HCl) and hypochlorous acid (HClO). The reaction indicates simultaneous oxidation and reduction of chlorine.

Question 37

Explain the use of chlorine in water treatment.

Answer 37

Chlorine is used to disinfect water, effectively killing bacteria and other pathogens in drinking water and swimming pools, despite its toxic properties. The benefits to public health outweigh the potential hazards when used correctly.

Question 38

What occurs when chlorine reacts with cold dilute sodium hydroxide?

Answer 38

When chlorine reacts with cold dilute sodium hydroxide, it forms sodium chloride (NaCl), sodium hypochlorite (NaClO), and water. This mixture is commonly used as a bleach and disinfectant.

Question 39

What is the principle behind hydrogen fuel cells?

Answer 39

Hydrogen fuel cells generate electricity through the reaction of hydrogen with oxygen, producing water as the only byproduct. They offer a clean alternative to fossil fuels, with water vapor being the main emission.

Question 40

What are some challenges associated with hydrogen fuel cells?

Answer 40

Key challenges include the high cost of production, difficulties in safely storing and transporting hydrogen, and the limited lifecycle of components. Ensuring a sustainable source of hydrogen through green methods is also critical.

Question 41

Describe and explain the trend in electronegativity down the group.

Answer 41

It decreases down the group. The size of the molecule increases down the group so the bonding electrons are further away from the positive nucleus; there is more shielding.

Question 42

Describe and explain the trend in boiling point down the group.

Answer 42

It increases down the group. As the size of the molecule increases, so do the Van der Waals’ forces and there are more electrons attracted to the positive nucleus. More energy is needed to overcome these forces.

Question 43

What are the advantages of adding chlorine to drinking water?

Answer 43

It kills disease-causing microorganisms, some chlorine persists in the water to prevent reinfection further down the supply, and it prevents the growth of algae, removes bad tastes and smells, and removes discolouration from organic compounds.

Question 44

What are the disadvantages of adding chlorine to drinking water?

Answer 44

Chlorine gas is harmful as it irritates the respiratory system, chlorine in a liquid form causes chemical burns, and water contains many organic compounds which could react with chlorine to form chlorinated hydrocarbons which are carcinogenic.

Question 45

Explain how forces arise between molecules of chlorine.

Answer 45

In chlorine molecules, temporary dipoles occur due to the random movement of electrons. These temporary dipoles induce dipoles in neighboring molecules, resulting in temporary attractions between the partially positive and partially negative ends of different molecules.

Question 46

What is the equation for the reaction of chlorine with water and why is chlorine added to drinking water?

Answer 46

Equation: Cl2 + H2O ↔ HCl + HClO. Chlorine is added to drinking water because it kills bacteria and other microorganisms, effectively disinfecting the water.

Question 47

Which sodium halide does not produce a sulfur-containing gas when reacted with concentrated sulfuric acid?

Answer 47

NaCl does not produce a sulfur-containing gas when reacted with concentrated sulfuric acid, unlike NaBr and NaI, which can produce gases like hydrogen sulfide and sulfur dioxide.

Question 48

Provide the equation and an observation for the reaction of solid sodium bromide with concentrated sulfuric acid.

Answer 48

2 H2SO4 + 2 NaBr → (Observation: Bromine gas is evolved, producing a brown solution.)

Question 49

What is the reaction of solid sodium bromide with concentrated sulfuric acid?

Answer 49

2H₂SO₄ + 2NaBr → Na₂SO₄ + SO₂ + Br₂ + 2H₂O

Observation: Orange/brown fumes of bromine are produced.

Question 50

How can chloride and iodide ions be detected using silver nitrate?

Answer 50

Add aqueous silver nitrate to the sample after treating with dilute nitric acid. Chloride forms a white precipitate of AgCl; iodide forms a pale yellow precipitate of AgI. Adding excess dilute ammonia dissolves AgCl but leaves AgI, helping differentiate between them.

Question 51

Why is chlorine used in water treatment despite being toxic?

Answer 51

Chlorine is used because it effectively kills bacteria and pathogens, making water safe for consumption. The health benefits outweigh the risks associated with its toxicity.

Question 52

What is the trend in boiling points down Group 7?

Answer 52

The boiling point increases down Group 7 due to the increase in van der Waals forces as the molecular size and number of electrons increase.

Question 53

How does the reactivity and properties of astatine compare to other halogens?

Answer 53

Astatine has a greater boiling point than bromine but is less effective as an oxidizing agent. It is the least reactive halogen and has properties that are more metallic than the other halogens.