10.Group 7, the halogens Flashcards
Describe the trend in size of atoms going down group 7
- going down the group atoms get bigger
- each element has one extra filled main level of electrons
Describe the trend in electronegativity going down in group 7
- electronegativity is the power of an atom to attract shared electrons in a covalent bond
- going down the group electronegativity decreases
- atoms get bigger and more shielding, going down a group
- less nuclear attraction between halogen nucleus and shared electrons electrons in the covalent bond
Describe the trend in melting and boiling points going down in group 7
- increase as you go down a group
- larger atoms have more electrons
- larger van der Waal forces
Define volatile
Easily evaporated at normal temperatures
Which is more volatile chlorine or iodine
- the lower the boiling point the more volatile the element
- so chlorine is more volatile
Describe the trend in oxidising ability going down a group
- going down a group the oxidising ability decreases
- shielding and atom radii increases going down
- nuclear attraction decreases
- this reduces the ability for atom to attract (accept) electrons
How do halogens react with metal halides
By displacement reaction. Halide in the compound will be displaced by a more reactive halogen.
Write the ionic equation for the extraction of bromine from sea water
Cl2 (aq) + 2Br- (aq) —> Br2 (aq) + 2Cl- (aq)
Describe how iodine is extracted from kelp
- salts such as NaCl KCL and K2S04 are removed by washing with water
- residue is then heated with manganese dioxide and conc. sulfuric acid and iodine is liberated
Write the ionic equation for the extraction of iodine from kelp
2I- +MnO2 + 4H+ —-> Mn2+ + 2H2O +I2
Describe the trend in reducing ability going down a group
- going down a group the oxidising ability increases
- shielding and atomic radii increases
- reducing nuclear attraction
- this increases the ability for atom to lose (donate) electrons
What reactions shows the trend in reducing ability
Reaction of solid sodium halides with conc. sulfuric acid
Name a observation when conc. sulfuric acid is added to NaCl
Steamy fumes of hydrogen chloride
Name the solid product when conc. sulfuric acid is added to NaCl
Hydrogensulfate
Write the equation for when conc. sulfuric acid is added to NaCl
NaCl (s) + H2SO4 (l) —> NaHSO4 (s) + HCl (g)
Is the reaction between conc. sulfuric acid and NaCl a redox reaction
- no
- as no oxidation state has changed
- the chlorine ion is too weak a reducing agent to reduce the sulphur
What kind of reaction is the reaction between conc. sulfuric acid and NaCl
Acid-base reaction
Name a observation when conc. sulfuric acid is added to NaBr
Steamy fumes of hydrogen bromide and brown fumes of bromine
What colour is bromine gas
Brown
Describe two reactions that occur when conc. sulfuric acid is added to NaBr
- first sodium hydrogensulfate and HBr are produced in an acid-base reaction
- bromide ions are strong enough reducing agents to reduce sulfuric acid to sulfur dioxide
Write the equations for when conc. sulfuric acid is added to NaBr and what reactions they are
1) NaBr (s) + H2SO4 (l) —-> NaHSO4 (s) + HBr (g)
an acid base reaction
2) 2H+ +2Br- + H2SO4 (l) —-> SO2 (g) + 2H2O (l) + Br2 (l)
a redox reaction
Name a observation when conc. sulfuric acid is added to NaI
- steamy fumes of HI
- black solid of iodine
- bad egg smell of hydrogen sulfide
Describe two reactions that occur when conc. sulfuric acid is added to NaI
- first sodium hydrogensulfate and HI are produced in an acid-base reaction
- iodine ions are better reducing agents so reduce the sulfuric acid even further to sulfur dioxide sulfur and hydrogen sulfide are produced
Write the equations for when conc. sulfuric acid is added to NaI and what reactions they are
1) NaI (s) + H2SO4 (l) —-> NaHSO4 (s) + HI (g)
an acid base reaction
2) 8H+ + 8I- + H2SO4 (l) —-> H2S (g) + 4H2O (l) + 4I2 (l)
a redox reaction
Write an ionic equation for reaction of metal chlorides with silver ions
Cl- (aq) +Ag+ (aq) —->AgCl (s)
Describe the steps in identifying metal halides with silver ions
- dilute nitric acid is added to the solution to get rid of any soluble carbonate or hydroxide impurities
- add a few drops of silver nitrate which forms the halide precipitate
How would carbonates or hydroxides interfere with identifying metal halides with silver ions
-forming silver carbonate
2Ag+ (aq) + CO3 2- (aq) —-> Ag2CO3 (s)
-forming silver hydroxide
Ag+ (aq) + OH- (aq) —-> AgOH (s)
Write the equations for getting rid of soluble carbonate or hydroxide impurities
CO3 2- (aq) + 2H+ (aq) —-> CO2 (g) + H2O (l)
OH- (aq) + H+ (aq) —-> H2O (l)
What are the results form the identifying metal halides with silver ions test
- silver fluoride :no precipitate
- silver chloride: white precipitate
- silver bromide: cream precipitate
- silver iodide: pale yellow precipitate
What further test can be done to distinguish silver halides
- add a few drop of a dilute ammonia
- then add a few drops of concentrated ammonia
- silver chloride: dissolves in dilute ammonia
- silver bromide: dissolves in conc. ammonia
- silver iodide: insoluble in conc. ammonia
Write the equation for the reaction between chlorine and water
Cl2 (g) +H2O (l) —> HClO (aq) + HCl (aq)
What kind of reaction is the reaction between chlorine and water
Disproportionation
What is a disproportionation reaction
Describes a redox reaction in which the oxidation number of some atoms of a particular element increases and that of other atoms of the same atom decrease
Name a use for the reaction between chlorine and water
Purify drinking water and swimming baths as the chloric acid kills bacteria by oxidation (as it is an oxidising agent)
It is also a bleach
Describe the reaction between chlorine and water in sunlight
2Cl2 (g) +2H2O (l) —-> 4HCl (aq) + O2 (g)
pale green —-> colourless
Describe an alternative to the direct chlorination of swimming pools
-add solid sodium (or calcium) chlorate (I). This dissolves in water to form chloric acid, HClO (aq)
Write an equation for sodium chlorate and water
NaClO (s) + H2O Na+ (aq) + OH- + HClO (aq)
Why do swimming pools with sodium chlorate dissolved need to be slightly acidic
-in alkaline solution the equilibrium moves to the left and the HClO is removed as ClO-
Write the equation for the reaction with chlorine and alkali
Cl2 (g) + 2NaOH (aq) —-> NaClO (aq) + NaCl (aq) + H2O (l)
Describe the reaction for the reaction with chlorine and alkali
Chlorine reacts with cold, dilute sodium hydroxide to form sodium chlorate (I), NaClO.
What is NaClO
- oxidising agent
- active ingredient in household bleach
What kind reaction of is the reaction with chlorine and alkali
Disproportionation
Name two disproportionation reactions
- chlorine + alkali
- chlorine + water
