Chapter 10- the Halogens Flashcards
How does electronegativity change down group 7?
Decreases down the group
-nuclear charge increases BUT
-atomic radius increases
-more shells
-more shielding
weaker attraction between nucleus and outer bonding electrons
How does boiling point change down group 7?
Increases down the group
-larger atoms and so diatomic molecules have more electrons
-VdWs forces between the molecules are stronger so require more energy to break
How does oxidising ability change down group 7 and where is this seen?
Decreases down the group (electronegativity decreases)
Halogens react with metal halides in solution in a displacement reaction, most reactive ends up in the compound
Flourine cannot be investigated (aq) as it reacts with water
How does reducing ability change down group 7 and where is this seen?
Increases down the group (electronegativity decreases)
Shown in reactions of sodium halides with concentrated sulfuric acid
How does sodium chloride (s) react with concentrated sulfuric acid?
NaCl (s) + H2SO4 (l) –> NaHSO4 (s)+ HCl (g)
-steamy fumes of HCl seen
-no oxidation state changed as chloride ion is too weak [R] to reduce the sulfur
-acid-base reaction
How does sodium bromide (s) react with concentrated sulfuric acid?
TWO reactions
NaBr (s) + H2SO4 (l) –> NaHSO4 (s) + HBr (g)
-steamy fumes of HBr and brown fumes of Br2
-no redox
2H+ + 2Br- + H2SO4 (l) –> SO2 (g) + 2H2O (l) + Br2 (l)
-bromide ions strong enough [R] to reduce sulfuric acid to sulfur dioxide, S [R] 6+ to 4+, Br [O] -1 to 0.
-redox reaction, exothermic
How does sodium iodide (s) react with concentrated sulfuric acid?
Several reactions
NaI (s) + H2SO4 (l) –> NaHSO4 (s) + HI (g)
-steamy fumes of HI, acid-base reaction
8H+ + 8I- + H2SO4 (l) –> H2S (g) + 4H2O (l) + 4I2 (s)
-black solid iodine, bad egg smell of H2S
-iodine ions better [R] so reduce sulfur from 6+ to 0 then 2-. Some yellow sulfur (s) may be seen when 0.
What is the test to identify halide ions?
-Add dilute nitric acid to remove impurities: OH- and CO3 2- ions which would interfere with the test
-Silver nitrate (AgNO3 (aq)) then added to form AgX (s)
-AgCl: white ppt, AgBr: cream ppt, AgI: pale yellow ppt
What happens when dilute then concentrated ammonia (NH3 (aq)) is added to the halide precipitates?
-Dilute: AgCl dissolves, colourless solution
-Concentrated: AgBr dissolves, colourless solution. AgI does not dissolve, stays pale yellow ppt
What happens when chlorine reacts with water (not in sunlight)?
Cl2 (g) + H2O (l) ⇌ HClO (aq) + HCl (aq)
-produces chloric (I) acid and hydrochloric acid
-Cl2 both reduced and oxidised: disproportionation
What are the uses of chlorine and chloric (I) acid?
Chlorine used to purify water for drinking and in swimming pools, to prevent diseases. Used despite its toxicity as used in low conc. and benefits outweigh risks.
Chloric (I) acid is an oxidising agent and kills bacteria by oxidation, also a bleach.
What happens when chlorine reacts with water in sunlight?
2Cl2 (g) + 2H2O (l) –> 4HCl (aq) + O2 (g)
-chlorine rapidly lost from pool water in sunlight so pools (mostly shallow) require frequent addition of Cl2.
How does chlorine react with cold, dilute sodium hydroxide and what are the products used for?
Cl2 (g) + 2NaOH (aq) –> NaClO (aq) + NaCl (aq) + H2O (l)
-disproportionation
-NaClO: sodium chlorate (I) is an oxidising agent and the active ingredient in household bleach
What is the test for group 2 ions?
React with NaOH (OH- ions) to form metal hydroxide.
-Add 10 drops of each, NaOH dropwise and shaking
Mg(OH)2- gelatinous white ppt
Ca(OH)2- white ppt (faintisih)
Sr(OH)2- faint white ppt
Ba(OH)2- colourless solution
OR WITH SULFATE IONS
What is the test for ammonium ions?
-React with NaOH
-Warm mixture in test tube gently in water bath
-Test fumes released using forceps and damp red litmus paper in the mouth of the test tube, will go blue if present
