Halogens

Question 1

What is the trend in electronegativity for Group 7 elements?

Answer 1

Decreases

Electronegativity decreases down the group due to increased principal energy levels.

Question 2

What is the trend in boiling point for Group 7 elements?

Answer 2

Increases

Boiling point increases due to more London forces needing to be broken as molecular size increases.

Question 3

What causes the decrease in electronegativity in Group 7 elements?

Answer 3

Weaker attraction between nucleus and electrons in a covalent bond

This is due to the increase in the number of principal energy levels.

Question 4

What happens to the size of atoms in Group 7 as you move down the group?

Answer 4

Increases

More electrons are added to the outer shells as you move down the group.

Question 5

What are the appearances of the halogen molecules at room temperature?

Answer 5

• Fluorine: Pale yellow gas
• Chlorine: Pale green gas
• Bromine: Dark red/orange liquid
• Iodine: Dark purple/black solid

The physical states and colors vary significantly among the halogens.

Question 6

Fill in the blank: The boiling point of halogens ______ as you descend the group.

Answer 6

Increases

Question 7

What is the definition of an oxidising agent?

Answer 7

An oxidising agent is a substance that is reduced and accepts electrons.

Question 8

How do halogens act as oxidising agents?

Answer 8

Halogens gain an electron and are reduced when acting as oxidising agents.

Question 9

What happens to the oxidising ability of halogens as you move down the group?

Answer 9

The ability of halogens to act as oxidising agents decreases.

Question 10

What are the reasons for the decrease in oxidising ability of halogens down the group?

Answer 10

The atomic radius increases, shielding increases, and the attraction from the nucleus weakens.

Question 11

What practical method can be used to test the oxidising ability of halogens?

Answer 11

Displacement reactions can be used to test the oxidising ability of halogens.

Question 12

What occurs during a displacement reaction involving halogens?

Answer 12

Aqueous solutions of halogens are added to an aqueous solution of a different halide salt, resulting in a color change.

Question 13

What effect does shaking the mixture with an organic solvent have on observing color changes?

Answer 13

Shaking with an organic solvent makes the color change easier to see as the halogen dissolves in a layer above the aqueous solution.

Question 14

What are the observations when Cl2 is added to KBr?

Answer 14

There is no visible change.

Question 15

What is the ionic equation for the reaction between Cl2 and KBr?

Answer 15

Cl2 + 2KBr → Br2 + 2KCl.

Question 16

What is observed when Cl2 is added to KI?

Answer 16

A brown solution is observed.

Question 17

What is the overall equation when Cl2 reacts with KI?

Answer 17

Cl2 + 2KI → I2 + 2KCl.

Question 18

What is the observation when Br2 is added to KI?

Answer 18

A purple solution is observed.

Question 19

Fill in the blank: The color of Cl2 in both aqueous solution and organic solvent appears _______.

Answer 19

colorless or pale green.

Question 20

What happens to the reactivity of halogens down the group?

Answer 20

Halogens become less reactive down the group.

Question 21

What is the full equation for the reaction of silver nitrate with halide ions?

Answer 21

AgNO3 + NaX → AgX + NaNO3

Question 22

What is the simplest ionic equation for the reaction involving silver ions and halide ions?

Answer 22

Ag+(aq) + X-(aq) → AgX

Question 23

What observation is made when F- is reacted with silver nitrate?

Answer 23

No visible change (as AgF is soluble)

Question 24

What observation is made when Cl- is reacted with silver nitrate?

Answer 24

White ppt

Question 25

What observation is made when Br- is reacted with silver nitrate?

Answer 25

Cream ppt

Question 26

What observation is made when I- is reacted with silver nitrate?

Answer 26

Yellow ppt

Question 27

What ions must be removed before testing for halide ions?

Answer 27

Hydroxide and carbonate ions

Question 28

How do we remove hydroxide and carbonate ions from the solution?

Answer 28

By acidifying the solution with nitric acid

Question 29

What is the overall reaction when acidifying the solution with nitric acid?

Answer 29

2HNO3 + Na2CO3 → 2NaNO3 + CO2 + H2O

Question 30

What is the ionic equation for the acidification reaction?

Answer 30

2H+ + CO32- → H2O + CO2

Question 31

Why should hydrochloric acid not be used to acidify the solution?

Answer 31

It contains Cl- and would form a precipitate of AgCl

Question 32

What is the solubility of AgF in dilute NH3?

Answer 32

Soluble

Question 33

What is the solubility of AgCl in dilute NH3?

Answer 33

Sparingly soluble

Question 34

What is the solubility of AgBr in dilute NH3?

Answer 34

Soluble

Question 35

What is the solubility of AgI in dilute NH3?

Answer 35

Insoluble

Question 36

How can AgCl(s) be distinguished from AgBr(s)?

Answer 36

AgCl dissolves in dilute NH3, AgBr does not

Question 37

How can AgBr(s) be distinguished from AgI(s)?

Answer 37

AgBr dissolves in concentrated NH3, AgI does not

Question 38

What is formed when chlorine dissolves in water?

Answer 38

A mixture of hydrochloric acid (HCl) and chloric(I) acid (HClO) ## Footnote This mixture is often referred to as chlorine water, which is pale green in color.

Question 39

What is the equilibrium reaction when chlorine dissolves in water?

Answer 39

Cl₂(g) + H₂O(l) = HCl(aq) + HClO(aq) ## Footnote This represents the chemical reaction involved in forming chlorine water.

Question 40

What oxidation states are associated with chlorine in the reaction?

Answer 40

0, -1, +1 ## Footnote Chlorine is both oxidized and reduced in the reaction.

Question 41

What is disproportionation in chemistry?

Answer 41

Oxidation and reduction of the same element ## Footnote This occurs in the reaction of chlorine in water.

Question 42

What happens to universal indicator paper when added to chlorine water?

Answer 42

It first turns red and then turns white ## Footnote The red color indicates the presence of strong and weak acids, while the white color indicates the bleaching effect of HClO.

Question 43

What are the uses of chlorine and its compounds?

Answer 43

Sterilizing drinking water and swimming pool water ## Footnote Chlorine is used to kill bacteria in water.

Question 44

Why is the concentration of chlorine monitored in swimming pools?

Answer 44

To ensure it is sufficient to kill bacteria without being toxic ## Footnote Chlorine is toxic and must be used in very small amounts.

Question 45

What can happen if chlorine levels in water are not carefully controlled?

Answer 45

Chlorine can react with organic compounds to form carcinogenic chlorinated hydrocarbons ## Footnote This risk is small compared to untreated water risks.

Question 46

What is a significant risk associated with untreated water?

Answer 46

Cholera ## Footnote Cholera is an infectious and often fatal bacterial disease.

Question 47

What is produced when chlorine reacts with water?

Answer 47

An equilibrium mixture of HC and HCLO ## Footnote The reaction is represented as Cl2(g) + H2O(l) ⇌ HC(aq) + HCLO(aq)

Question 48

What happens when chlorine reacts with cold dilute sodium hydroxide?

Answer 48

The reaction produces water, sodium chloride, and sodium chlorate ## Footnote The reaction can be written as Cl2 + 2NaOH → H2O + NaCl + NaClO

Question 49

What is the ionic equation for the reaction of chlorine with cold dilute sodium hydroxide?

Answer 49

Cl2 + 2OH⁻ → H2O + Cl⁻ + ClO⁻ ## Footnote This shows the ionic species involved in the reaction.

Question 50

What is the commercial importance of the reaction of chlorine with sodium hydroxide?

Answer 50

It produces sodium chlorate, NaClO, which is used in household bleach ## Footnote Sodium chlorate is the active ingredient in many bleaching agents.

Question 51

Fill in the blank: The reaction of chlorine with cold dilute sodium hydroxide produces _______ as one of its products.

Answer 51

sodium chlorate

Question 52

What is the test for Ammonium (NH4*)?

Answer 52

Warm the sample with sodium hydroxide solution in a test tube and test the gas produced with moist litmus paper. ## Footnote The gas produced is alkaline (ammonia) so will turn the moist litmus paper blue.

Question 53

What is the result of adding acidified silver nitrate solution followed by aqueous ammonia to a solution containing Chloride (Cl)?

Answer 53

White ppt, which dissolves in dilute aqueous ammonia to give a colourless solution. ## Footnote This is a characteristic reaction for Chloride ions.

Question 54

What is the result of adding acidified silver nitrate solution followed by aqueous ammonia to a solution containing Bromide (Br)?

Answer 54

Cream ppt, which is insoluble in dilute aqueous ammonia but dissolves in concentrated ammonia to give a colourless solution. ## Footnote This distinguishes Bromide from Chloride.

Question 55

What is the result of adding acidified silver nitrate solution followed by aqueous ammonia to a solution containing Iodide (I)?

Answer 55

Yellow ppt, which is insoluble in dilute and concentrated aqueous ammonia. ## Footnote This indicates the presence of Iodide ions.

Question 56

What is the test for Sulfate (SO4)?

Answer 56

Make a solution of the compound and add some acidified barium nitrate solution. ## Footnote A white ppt of BaSO4 indicates the presence of Sulfate ions.

Question 57

What is the test for Carbonate (CO3)?

Answer 57

Add some dilute nitric acid and test the gas produced with limewater. ## Footnote Effervescence and the gas produced will turn the lime water cloudy, indicating Carbonate.

Question 58

What does effervescence indicate when testing for Carbonate (CO3)?

Answer 58

The production of gas that turns lime water cloudy. ## Footnote This gas is carbon dioxide (CO2).

Question 59

What does disproportionation mean?

Answer 59

Oxidation and reduction of same element