The halogens and halides (CHEMISTRY)
Describe the physical properties of the halogens (at room temperature)
Fluorine - Pale yellow gas
Chlorine - Greenish gas
Bromine - Red-brown liquid
Iodine - Black solid
What is the trend for the size of the atoms of Group 7?
Bigger going down the group because each element above has one extra filled main level of electrons compared with the one above it.
What is electronegativity?
The ability of an atom to attract electrons towards itself within a covalent bond.
What is the trend of electronegativity for Group 7?
Decreases going down the group because the atomic radius increases down the group. (more shells = more shielding = weaker forces)
What is the trend for MP/BP for Group 7?
They increase going down the group because the atoms have more electrons and this makes the Van der Waals forces between the molecules stronger.
What happens to the oxidising activity of the halogens?
The oxidising ability of the halogens increases going up the group.
What happens during a displacement reaction? (For the halogens)
Halogens will react with metal halides in solution so that the halide in the compound will be displaced by a more reactive halogen.
Describe the trend for reducing power for going down Group 7 and explain why
It increases because the ionic radius increases going down the group, making it easier to lose electrons due to weaker forces.
Briefly describe the sodium chloride reaction
- Drops of HCl are added to solid sodium chloride
- Steamy fumes of hydrogen chloride can be seen
- The solid product is sodium hydrogensulfate.
Write the symbol equation for the sodium chloride reaction
NaCl(s) + H2SO4(l) -> NaH2SO4(s) + HCl (l)
True or false: The sodium chloride reaction is a redox reaction. It is not an acid-base reaction.
False. No oxidation states have changed and chloride is too weak to reduce the sulfur. It is only an acid-base reaction
Briefly describe the sodium bromide reaction
(- Drops of HCl are added to solid sodium bromide?)
- Steamy fumes of hydrogen bromide and brown fumes of bromine can be seen
What is the symbol equation for the sodium bromide reaction (acid-base)
NaBr(s) + H2SO4(l) -> NaHSO4(s) + HBr(g)
What is the symbol equation for the sodium bromide reaction (redox)
2H+ +2Br- + H2SO4(l) -> SO2(g) + 2H2O(l) +Br2(l)
-1 +6 +4 0
Are the reactions for the sodium chloride reaction exothermic or endothermic?
The reactions are exothermic and some of the bromine vaporises
Briefly describe the sodium bromide reaction
- Steamy fumes of iodine
- Bad egg smell of hydrogen sulfide gas
- Yellow solid sulfur
- Colourless sulfur dioxide
- (Drops of HCl are added to solid sodium iodide?)
What is the symbol equation for the sodium iodide reaction? (acid-base)
NaI(s) + H2SO4(l) -> NaHSO4 (s) + HI(g)
What is the symbol equation for the sodium iodide reaction? (redox)
8H+ + 8I- + H2SO4(l) -> H2S(g) + 4H20(l) + 4I2(s)
-1 +6 -2 0
True or false: Iodide ions are better reducing agents than bromide ions
True. Iodide ions are better at reduction
What can be seen during the reduction of sulphuric acid by iodide ions?
- +6
- 0 Solid yellow sulphur
- -2
What can be seen during a silver fluoride test?
No precipitate (fluoride does not react with metal halides
What can be seen during a silver chloride test? (and a further test)
- White precipitate
- A further test reveals that it dissolves in dilute ammonia
What can be seen during a sodium bromide test? (and a further test)
- A cream precipitate
- It dissolves in concentrated ammonia
What can be seen during the silver iodide reaction? (and a further test)
- A pale yellow precipitate
- It is insoluble in concentrated ammonia
What is the symbol equation for the reversible reaction used to form HClO? (No sunlight)
Cl2(g) + H20(l) -> HClO(aq) + HCl(aq)
0 <- +1 -1
What is the symbol equation for the reversible reaction used to form HClO? (In sunlight)
2Cl2(g) + 2H2O(l) -> 4HCl(aq) + O2(g)
pale green colourless
What is an alternative to the chlorination of pools?
To add solid sodium (or calcium) chlorate which dissolves in water to form chloric acid
What is the symbol equation for the alternative solution for the chlorination of pools?
NaClO(s) + H2O -> Na+ (aq) + OH-(aq) + HClO(aq)
<-
What happens to the equilibrium of the alternative reaction in alkaline solutions?
The equilibrium shifts to the left and the HClO is removed as ClO- ions
What is formed when chlorine reacts with cold, dilute sodium hydroxide?
Sodium chlorate which is an oxidising agent
What kind of reaction occurs when chlorine reacts with cold, dilute sodium hydroxide?
A disproportionation reaction
What is the symbol equation for chlorine reacting with cold, dilute sodium hydroxide to form sodium chlorate?
Cl2(g) + 2NaOH(aq) -> NaClO(aq) + NaCl(aq) +H2O(l)
0 +1 -1