3.2.3 - Group 7 - The Halogens

Question 1

Atomic radius

Answer 1

increases down the group due to additional electron shells

Question 2

Reactivity

Answer 2

Decreases down the group due to increased shielding

Question 3

Ionisation energy

Answer 3

Decreases down the group due to increasing atomic radius and shielding

Question 4

Boiling point

Answer 4

Increases down the group as van der Waals forces increase down the group

Question 5

Oxidising power

Answer 5

Decreases down the group as ability to attract electrons decreases due to shielding and increased atomic radius

Question 6

Halide ions

Answer 6

negative ions of halogens

Question 7

Reducing power

Answer 7

Increases down the group as electrons are easier to lose from larger ions due to shielding and increased atomic radius.

Question 8

Halide ions as reducing agents

Answer 8

Good reducing agents as they donate electrons to the species being reduced and are oxidised themselves

Question 9

Equation for redox reaction with H2SO4 and NaF

Answer 9

NaF + H2SO4 –> NaHSO4 + HF

Question 10

Equation for redox reaction with H2SO4 and NaCl

Answer 10

NaCl + H2SO4 –> NaHSO4 + HCl

Question 11

Equation for redox reaction with H2SO4 and NaBr

Answer 11

NaBr + H2SO4 –> NaHSO4 + HBr
2HBr + H2SO4 –> Br2 + SO2 + 2H2O

Question 12

Equation for redox reaction with H2SO4 and NaI

Answer 12

NaI + H2SO4 –> NaHSO4 + HI
2HI + H2SO4 –> I2 + SO2 + 2H2O
6HI + SO2 –> H2S + 3I2 + 2H2O

Question 13

Acidified silver nitrate

Answer 13

Can be used to test for halide ions

Question 14

AgNO3 and Cl-

Answer 14

white precipitate

Question 15

AgNO3 and Br-

Answer 15

cream precipitate

Question 16

AgNO3 and I-

Answer 16

yellow precipitate

Question 17

dilute NH3 and Cl-

Answer 17

precipitate dissolves

Question 18

dilute NH3 and Br-

Answer 18

no visible reaction

Question 19

dilute NH3 and I-

Answer 19

no visible reaction

Question 20

conc NH3 and Cl-

Answer 20

precipitate dissolves

Question 21

conc NH3 and Br-

Answer 21

precipitate dissolves

Question 22

conc NH3 and I-

Answer 22

no visible reaction

Question 23

Products of reaction between chlorine and cold water

Answer 23

Produces chlorate (I) ions (ClO-) and chloride ions

Question 24

Equation for reaction between cold water and chlorine

Answer 24

Cl2 + H2O –> ClO- + Cl- + 2H+

Question 25

Reaction between chlorine and cold water

Answer 25

disproportionation reaction

Question 26

Chlorine in UV light

Answer 26

decomposes to produce oxygen and hydrochloric acid, chlorine is reduced

Question 27

Equation for reaction between chlorine and cold water in the presence of UV light

Answer 27

2Cl2 + 2H2O --> 4HCl + O2

Question 28

Chlorine uses

Answer 28

used in small quantities to kill bacteria in water treatment processes as chlorine is toxic

Question 29

Reaction to produce bleach from chlorine

Answer 29

Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite

Question 30

Equation to produce bleach from chlorine

Answer 30

2NaOH + Cl2 --> NaClO + NaCl + H2O

Question 31

Test for sulfate ions

Answer 31

use BaCl2 which forms a white precipitate

Question 32

Test for hydroxide ions

Answer 32

use red litmus paper which turns blue, or universal indicator which turns blue-purple

Question 33

Test for carbonate ions

Answer 33

Add and acid such as HCl the substance containing the carbonate ion will produce effervescence and CO2 gas is given off. Gas can be collected and bubbled through limewater which will turn cloudy confirming CO2

Question 34

Flame colour for Ca2+

Answer 34

brick red

Question 35

Flame colour for Sr2+

Answer 35

red

Question 36

Flame colour for Ba2+

Answer 36

pale green

Question 37

Test for NH4+ ions

Answer 37

Holding red litmus paper over a Petri dish of the substance being tested, it will turn blue if ammonium ions are present. Can also be tested in the same way but adding NaOH to produce ammonium gas faster