Elements from the Sea

Question 1

Appearance of the halogens at room temperature

Answer 1

• Fluorine: pale yellow gas
• Chlorine: green gas
• Bromine: dark red volatile liquid
• Iodine: black solid, sublimes to purple vapour

Question 2

Trends going down group 7

Answer 2

• Become darker in colour
• Melting and boiling point increase
• Change from gases to liquids to solids at room temperature
• Become less volatile

Question 3

Oxidation

Answer 3

• Loss of hydrogen
• Loss of electrons
• Increase in oxidation state

Question 4

Reduction

Answer 4

• Gain of hydrogen
• Gain of electrons
• Decrease in oxidation state

Question 5

Products of electrolysis at the cathode

Answer 5

• Hydrogen if the metal comes from group 1 or 2 or is aluminium
• Metal for all other salts
• Hydrogen is made on the electrolysis of acids

Question 6

Products of electrolysis at the anode

Answer 6

• Halogen if the salt is a halide
• Oxygen if the salt is a sulphate or nitrate
• Oxygen is made on electrolysis of hydroxides

Question 7

Anode and cathode, oxidation and reduction

Answer 7

Reduction happens at the cathode

Oxidation happens at the anode

Question 8

Dynamic Equilibrium

Answer 8

• Concentrations of reactions and products stay constant
• Forward and reverse reactions are both happening
• The rate of the forward and reverse reactions are equal to each other

Question 9

Atom economy

Answer 9

Relative formula mass of the desired product/Relative formula mass of all reactants used

Question 10

Thermal stability down group 7

Answer 10

The thermal stability down group 7 increases because the bond strength between hydrogen and the halogen decreases as you go down group 7

Question 11

What happens when halides are heated in a lab

Answer 11

• Hydrogen fluoride isn’t broken down into hydrogen and fluorine
• Hydrogen chloride isn’t broken down into hydrogen and chlorine
• Some bromine gas is made when hydrogen bromide is strongly heated
• Large amounts of iodine are made if a red hot needle is plunged into hydrogen iodide

Question 12

Acidity in group 7

Answer 12

Apart from HF, all the hydrogen halides fully dissociate

Question 13

Halides reaction with sulphuric acid

Answer 13

• Hydrogen fluoride and hydrogen chloride do not react
• Hydrogen bromide makes sulphur dioxide, SO2
• Hydrogen iodide makes hydrogen sulphide, H2S

Question 14

Le Chatelier’s Principle

Answer 14

If a system is at equilibrium and a change is imposed, the system will oppose this change

Question 15

Effect of concentration on equilibrium

Answer 15

• Increasing the concentration of the reactants will cause equilibrium to shift to the side of the products
• Decreasing the concentration of the reactants will cause equilibrium to shift to the side of the reactants

Question 16

Effect of pressure on equilibrium

Answer 16

• Increasing the pressure will cause equilibrium to shift to the side with fewer moles of gas
• Decreasing the pressure will cause equilibrium to shift to the side will more moles of gas

Question 17

Effect of temperature on equilibrium

Answer 17

If endothermic:

• Increasing the temperature will cause equilibrium to shift to the products side
• Decreasing the temperature will cause equilibrium to shift to the reactants side

If exothermic:

• Increasing the temperature will cause equilibrium to shift to the reactants side
• Decreasing the temperature will cause equilibrium to shift to the products side