Inorganic - 2.3 Group 7

Question 1

Define displacement

Answer 1

Chemical reaction in which one element replaces another element in a compound. A halogen would displace a halide from solution if the halide is below it in the periodic table.

Question 2

What is a disproportionation reaction?

Answer 2

A reaction in which substance is simultaneously reduced and oxidised. Chlorine undergoes disproportionation in the reaction with cold dilute aqueous sodium hydroxide.

Question 3

Define electronegativity

Answer 3

The tendency of an atom to attract a bonding pair of electrons in a covalent bond

Question 4

Define oxidising ability

Answer 4

Oxidising ability is the ability to act as an oxidising agent. The oxidising ability of the halogens decreases down the group. This is because down the group the atoms get larger so the electrons are less strongly attracted to the nucleus so it’s harder to gain an electron.

Question 5

Define reducing ability

Answer 5

Reducing ability is the ability to act as a reducing agent. The reducing ability, or reducing power, of the halides increases down the group. This is because to act as a reducing agent the halide needs to lose an electron. As you go down the group it is easier for a halide to lose an electron because the attraction from the outer electron and nucleus decreases due to increase shielding and an increasing ionic radius.

Question 6

NaCl + H2SO4

Answer 6

Products: HCl

Reaction type: Acid-base

NaCl + H2SO4 -> NaHSO4 + HCl

Steamy Fumes

Question 7

NaBr + H2SO4

Answer 7

Products: HBr

Reaction type: acid-base

NaBr + H2SO4 -> NaHSO4 + HBr

Steamy fumes

Question 8

NaI + H2SO4

Answer 8

Products: HI

Reaction type: Acid-base

NaI + H2SO4 -> NaHSO4 + IH

Steamy fumes

Question 9

2Br- + H2SO4

Answer 9

Products: SO2

Reaction type: reduction of H2SO4

2Br- + H2SO4 + 2H+ -> Br2 + SO2 + 2H2O

Colourless gas

Question 10

2I- + H2SO4

Answer 10

Products: SO2

Reaction type: reduction of H2SO4

2I- + H2SO4 + 2H+ -> I2 + SO2 + 2H2O

Colourless gas

Question 11

6I- + H2SO4

Answer 11

Product: yellow solid (S)

Reaction type: reduction of H2SO4

6I- + H2SO4 + 6H+ -> 3I2 + S + 4H2O

Yellow solid

Question 12

8I- + H2SO4

Answer 12

Product: H2S

Reaction type: reduction of H2SO4

8I- + H2SO4 + 8H+ -> 4I2 + H2S + 4H2O

Bad egg gas

Question 13

2I- + H2SO4

Answer 13

Products: I2

Reaction type: oxidation of I-

2I- + H2SO4 + 2H+ -> I2 + SO2 + 2H2O

Purple fumes

Question 14

2Br- + H2SO4

Answer 14

Products: Br2

Reaction type: oxidation of Br-

2Br- + H2SO4 + 2H+ -> Br2 + SO2 + 2H2O

Brown fumes

Question 15

What are the physical properties of fluorine?

Answer 15

Poisonous yellow gas

Question 16

What are the physical properties of chlorine?

Answer 16

Poisonous, dense, yellow green gas

Question 17

What are the physical properties of bromine?

Answer 17

Toxic, red brown, volatile liquid.
(Red brown vapour)

Question 18

Why are the physical properties of iodine?

Answer 18

Shiny, grey black solid, sublime to form of violet vapour

Question 19

What are the physical properties of astatine?

Answer 19

Rarest naturally occurring element (no stable isotopes).
May be dark and have a higher melting point that iodine .

Question 20

Why do halogens exist as diatomic molecules?

Answer 20

They have a single covalent bond between atoms

Question 21

How does bond enthalpy change with atomic number?

Answer 21

The mean bond enthalpy decreases as atomic number increases for chlorine, bromine and iodine.

Question 22

What are the trends in group 7 down the group?

Answer 22

• The colour of the elements becomes darker
• The atomic radius increases (more shells)
• The reactivity decreases (increase shielding)
• The boiling point increases (more electrons so more induced dipole-dipole attraction)
• The electronegativity decreases (more shielding so weaker attraction between bonding electrons and nucleus so lower electronegativity value)