Group 7

Question 1

How does reactivity change as you go down group 7?

Answer 1

reactivity decreases down the group as it is harder to attract an electron due to atomic radius increasing so attracting an electron is harder as the positive attraction of the nucleus is weakened by additional shielding

Question 2

How does the atomic radius change as you go down group 7?

Answer 2

increases down the group due to additional electron shells

Question 3

How does the first ionisation energy change down group 7?

Answer 3

generally decreases down the group due to a greater atomic radius and increased amount of shielding

Question 4

What is the reaction of sodium fluoride and sulfuric acid?

Answer 4

NaF + H2SO4 -> NaHSO4 + HF

Question 5

What is the reaction of sodium chloride with sulfuric acid?

Answer 5

NaCl + H2SO4 -> NaHSO4 + HCl

Question 6

What is the reaction of sodium bromide with sulfuric acid?

Answer 6

NaBr + H2SO4 -> NaHSO4 + HBr

Question 7

What is the reaction of hydrogen bromide with sulfuric acid?

Answer 7

2HBr + H2SO4 -> Br2 + SO2 + 2H2O

Question 8

What is the reaction of sodium iodide with sulfuric acid?

Answer 8

NaI + H2SO4 -> NaHSO4 + HI

Question 9

What is the reaction of hydrogen iodide with sulfuric acid?

Answer 9

2HI + H2SO4 -> I2 + SO2 + 2H2O

Question 10

What is the reaction of hydrogen iodide with sulfur dioxide?

Answer 10

6HI + SO2 -> H2S + 3I2 + 2H2O

Question 11

At room temp. what is the physical appearance of fluorine?

Answer 11

a very pale yellow gas

Question 12

At room temp. what is the physical appearance of chlorine?

Answer 12

a greenish gas

Question 13

At room temp. what is the physical appearance of bromine?

Answer 13

orange/brown liquid which vaporises easily into an orange gas

Question 14

At room temp. what is the physical appearance of iodine?

Answer 14

a black solid which vaporises on heating to a purple gas

Question 15

Do the elements tend to get lighter or darker going down the group?

Answer 15

darker

Question 16

Do the elements tend to get lighter or denser going down the group?

Answer 16

denser

Question 17

What is electronegativity?

Answer 17

the ability of an atom to withdraw electron density from a covalent bond

Question 18

What does electronegativity depend on?

Answer 18

• a greater nuclear charge will withdraw electrons more strongly
• a shorter atomic radius will also help withdraw electrons more strongly
• the more shielding will however reduce the amount of electrons that can be withdrawn

Question 19

What is the general trend of electronegativity as you go down group 7?

Answer 19

decreases

Question 20

Are halogens polar or non-polar molecules?

Answer 20

non-polar

Question 21

What are the only intermolecular forces existing between halogen molecules?

Answer 21

Van der Waals forces

Question 22

The strength of the Van der Waals forces between halogen molecules is dependent on what?

Answer 22

the size of the molecule/how many electrons it has

Question 23

What is the general trend in melting and boiling point as you go down the group (7)?

Answer 23

increases as Van der Waals forces increase

Question 24

What state is fluorine at room temp.?

Answer 24

gas

Question 25

What state is chlorine at room temp.?

Answer 25

gas

Question 26

What state is bromine at room temp.?

Answer 26

liquid

Question 27

What state is iodine at room temp.?

Answer 27

solid

Question 28

Are halogens oxidising or reducing agents?

Answer 28

oxidising agents

Question 29

What is the trend in oxidising power of halogens as you go down group 7?

Answer 29

decreases

Question 30

During a halogen displacement reaction the halogen highest up group 7 should form what?

Answer 30

a halide ion

Question 31

During a halogen displacement reaction, the halogen lowest down group 7 should form a what?

Answer 31

halogen molecule

Question 32

Are halide ions oxidising or reducing agents?

Answer 32

reducing agents

Question 33

What is the trend in reducing power of halides as you go down group 7?

Answer 33

increases

Question 34

What is the equation of sodium fluoride reacting with sulfuric acid? (F- is not a powerful enough reducing agent so will undergo an acid-base reaction)

Answer 34

NaF(s) + H2SO4(aq) -> NaHSO4(s) + HF(g)

Question 35

What are the observations of sodium fluoride reacting with sulfuric acid?

Answer 35

- sodium hydrogen sulfate is the solid product formed - steamy fumes of hydrogen fluoride gas is released

Question 36

Is hydrogen fluoride gas safe?

Answer 36

it is extremely dangerous

Question 37

What is hydrogen fluoride gas used for?

Answer 37

to etch glass

Question 38

What is the equation of sodium chloride reacting with sulfuric acid? (Cl- is not a powerful enough reducing agent so will undergo an acid-base reaction)

Answer 38

NaCl(s) + H2SO4(aq) -> NaHSO4(s) + HCl (g)

Question 39

What are the observations of the reaction between sodium chloride and sulfuric acid?

Answer 39

- sodium hydrogen sulfate is the solid product formed - steamy fumes of hydrogen chloride gas is released

Question 40

Is a bromide ion a good reducing agent?

Answer 40

yes

Question 41

How will bromide ions react with sulfuric acid?

Answer 41

- initially it will undergo an acid-base reaction with H2SO4: NaBr(s) + H2SO4(aq) -> NaHSO4(s) + HBr(g) - the bromide ions in HBr will then react further, reducing sulfur: 2H+ + H2SO4 + 2Br- -> SO2 + 2H2O + Br2

Question 42

What are the observations of sodium bromide reacting with sulfuric acid? (at the end)

Answer 42

- an acidic gas forms - brown fumes of bromine gas appear

Question 43

Is I- a good reducing agent?

Answer 43

It is an excellent reducing agent

Question 44

What is the equation for the initial acid-base reaction of iodide ions with sulfuric acid?

Answer 44

NaI(s) + H2SO4(aq) -> NaHSO4(s) + HI(g)

Question 45

After an initial acid-base reaction of iodide ions with sulfuric acid, what are the three ways the iodide ions now in HI can react?

Answer 45

1, iodide ions can reduce the sulfur from (VI) in H2SO4 to (IV) in SO2(g) 2, iodide ions can reduce sulfur from (VI) in H2SO4 to (0) in S(s) 3, iodide ions can reduce sulfur from (VI) in H2SO4 to (-2) in H2S(g)

Question 46

What is the equation of iodide ions (from HI) reducing the sulfur from (+6) in H2SO4 to (+4) in SO2? And what are the observations?

Answer 46

2H+ + H2SO4 + 2I- -> SO2 + 2H2O + I2 an acidic gas forms and a black solid of iodine forms

Question 47

What is the equation of iodide ions (from HI) reducing sulfur from (+6) in H2SO4 to (0) in the element S? And what are the observations?

Answer 47

6H+ + H2SO4 + 6I- -> S + 4H2O + 3I2 Yellow solid sulfur produced and black solid of iodine forms

Question 48

What is the equation of iodide ions (from HI) reducing sulfur from (+6) in H2SO4 to (-2) in the H2S(g)? And what are the observations?

Answer 48

8H+ + H2SO4 + 8I- -> H2S + 4H2O + 4I2 Gas smelling of bad eggs and black solid of iodine forms

Question 49

What is the equation of silver ions reacting with fluoride ions?

Answer 49

Ag+(aq) + F-(aq) -> AgF(aq)

Question 50

When silver ions react with fluoride ions, what is the observation?

Answer 50

a clear and colourless solution

Question 51

What is the equation of silver ions reacting with chloride ions?

Answer 51

Ag+(aq) + Cl-(aq) -> AgCl(aq)

Question 52

When chloride ions react with silver ions, what is the observation?

Answer 52

a white precipitate

Question 53

What is the equation of silver ions reacting with bromide ions?

Answer 53

Ag+(aq) + Br-(aq) -> AgBr(aq)

Question 54

When silver ions react with bromide ions, what is the observation?

Answer 54

a cream precipitate

Question 55

What is the equation for the reaction of silver ions with iodide ions?

Answer 55

Ag+(aq) + I-(aq) -> AgI(aq)

Question 56

When silver ions react with iodide ions, what is the observation?

Answer 56

a yellow precipitate

Question 57

What are the steps if you have an unknown substance and wish to test for the presence of halide ions?

Answer 57

1, to the unknown sample, add a few drops of nitric acid (HNO3) - this is needed to remove any carbonate ions which may be present in the sample and can alter the results 2, add a few drops of silver nitrate solution (AgNO3) and use the observation to draw your conclusion

Question 58

What does no precipitate indicate in a test for halide ions?

Answer 58

no halides are present or fluoride is present

Question 59

What does a white precipitate indicate in a test for halide ions?

Answer 59

the presence of chloride ions

Question 60

What does a cream precipitate indicate in a test for halide ions?

Answer 60

the presence of bromide ions

Question 61

What does a yellow precipitate indicate in a test for halide ions?

Answer 61

the presence of iodide ions

Question 62

What reagent should you add if you want to confirm the results of the halide ions test?

Answer 62

ammonia

Question 63

What are the results when confirming halide ions presence with ammonia and what do they mean?

Answer 63

- the white ppt. for chloride ions will dissolve easily in dilute ammonia - the cream ppt. for bromide ions won't dissolve in dilute ammonia but will dissolve in conc. ammonia - the yellow ppt. for iodide ions is completely insoluble even in conc. ammonia

Question 64

If chlorine is a gas, can it dissolve in water?

Answer 64

Yes

Question 65

What is the hazard surrounding chlorine?

Answer 65

it is poisonous and can be extremely dangerous in high concentrations

Question 66

What are some common uses of chlorine and why?

Answer 66

used in the treatment of drinking water and swimming pools as in very low concentrations chlorine and its derivatives are perfectly safe for humans, but can kill bacteria

Question 67

When chlorine reacts with water, what products are formed?

Answer 67

chloric (I) acid and hydrochloric acid

Question 68

What is the equation for the reversible reaction between chlorine and water?

Answer 68

Cl2(g) + H2O(l) <-> HClO(aq) + HCl(aq)

Question 69

What is special about the reaction of chlorine with water?

Answer 69

It is a disproportionation reaction

Question 70

Why is the reaction of chlorine with water a disproportionation reaction?

Answer 70

the chlorine starts off in a zero oxidation state but gets reduced down to -1 in HCl and oxidised up to +1 in HClO at the same time

Question 71

When does the disproportionation reaction between chlorine and water occur and why is it useful?

Answer 71

when chlorine is used to treat drinking water as well as used to keep swimming pools clean - the chloric acid (HClO) is an oxidising agent and kills bacteria by oxidising them and HClO is also a bleach

Question 72

What is the reaction of chlorine with water in the presence of bright sunlight (UV light)? What is the colour change?

Answer 72

2Cl2(g) + 2H2O(l) -> 4HCl(aq) + O2(aq) pale green (the chlorine) to colourless (the hydrochloric acid)

Question 73

Why is the reaction of chlorine with water in the presence of UV light a problem?

Answer 73

because of this reaction, chlorine is rapidly lost from outdoor swimming pools and so needs to be constantly added

Question 74

What is an alternative to direct chlorination of swimming pools?

Answer 74

add solid sodium chlorate (NaClO) or calcium chlorate (Ca(ClO)2) as these both dissolve in water to form chloric acid in a reversible reaction: NaClO(s) + H2O(l) <-> Na+(aq) + OH- (aq) + HClO(aq) In alkaline solution the equilibrium above moves to the left which means HClO is converted to ClO- ions and for this reason swimming pool water is kept slightly acidic

Question 75

When chlorine reacts with cold dilute sodium hydroxide, what products are formed?

Answer 75

sodium chlorate

Question 76

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

Answer 76

Cl2(g) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) + H2O(l)

Question 77

What is sodium chlorate?

Answer 77

an oxidising agent and a component of household bleach

Question 78

Is the reaction of chlorine with cold dilute sodium hydroxide a disproportionation reaction?

Answer 78

yes