Group 7 (the halogens) Flashcards
Fluorine (colour, state and reactivity)
Pale yellow gas, highly reactive
Chlorine (colour, state and effect)
Green reactive gas, poisonous in high concentrations.
Bromine (colour, state and look)
Red liquid, with dense orange poisonous fumes.
Iodine (colour, state and look)
Shiny grey solid to purple gas
Trend in melting point and boiling point (halogens) and why
Increase down the group.
Molecules become larger, more electrons, larger VDW btwn molecules. More energy to break.
Trend in electronegativity (halogens), why?
Decrease. Atomic radii increases due to increasing number of shells. Nucleus less able to attract the b.p. of electrons.
Define electronegativity
Electronegativity is the relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself.
Trend in oxidising ability (halogens)
What are oxidising agents?
Decreases down the group.
Electron acceptors
Test tube reactions of solutions of the halogens with solutions containing their halide ions.
KCl:
Chlorine (no reaction) pale green
Bromine (no reaction) yellow
Iodine (no reaction) brown
KBr:
Chlorine (Br displaced) yellow
Bromine (no reaction) yellow
Iodine (no reaction) brown
KI:
Chlorine (I displaced) brown
Bromine (I displaced) brown
Iodine (no reaction) brown
How is the test solution for halide ions made?
The test solution is made acidic with nitric acid and then silver nitrate solution is added drop wise.
What is the role of the nitric acid in the test for halide ions?
To react with any carbonates present to prevent formation of Ag2CO3.
What precipitate does fluorides, chlorides, bromides and iodides make?
What can be added to differentiate them if the colours are similar?
Fluoride- no precipitate
Chloride- white precipitate
Bromide- cream precipitate
Iodides- pale yellow precipitate
Ammonia
How does each precipitate react with ammonia?
Silver chloride dissolves in DILUTE ammonia to form a complex ion (colourless sltn)
Silver bromide dissolves in CONC. ammonia (colourless sltn)
Silver iodide does not react with ammonia, too insoluble
Trend as reducing agents (halides)
Increasing down the group.
Explanation of differing reducing power of halides
A reducing agents donates electrons.
Reducing power of halides increases down group 7. They have greater tendency to donate electrons bcs the ions gets bigger so easier for outer electrons to be given away as pull from nucleus becomes smaller.
Observation of fluoride and chloride reactions with conc. sulfuric acid
NaF + H2SO4 -> NaHSO4 + HF (white steamy fumes)
NaCl+ H2SO4 -> NaHSO4 + HCl (white steamy fumes)
Bromide as a reducing agent and equations and observations
Acid-base step: NaBr + H2SO4 -> NaHSO4 + HBr
Redox step: 2H+ + 2Br- + H2SO4 -> Br2 + SO2 + 2H2O
Overall: 2NaBr + 3H2SO4 -> 2NaHSO4 + SO2 + BR2 + 2H2O
Observation: white steamy fumes, orange fumes of bromine, colourless acidic SO2 gas
Observations of Idide as a reducing agent.
White steamy fumes of HI
Black solid and purple fumes
Colourless acidic gas SO2
Sulfur yellow solid
H2S gas with bad egg smell
What is disproportionation?
It is the name for a reaction where an element simultaneously reduces and oxidises
Formula of reaction of chlorine with water to form chloride ions and chlorite ions
Formula for reaction if chloride with water to form chloride ions and oxygen
What will happen if universal indicator is added?
Cl2 + H2O (back and forth) HClO + HCl
2Cl2 + 2H2O -> 4H+ + 4 Cl- + O2 (in sunlight chlorine bubbles through water)
Red then colourless as HClO bleaches the colour
What is the greenish colour due to?
Cl2
What will happen if cold NaOH is added to Cl2, Br2 and I2
Colour will fade to colourless.
Reaction of chloride with NaOH and what will the mixture of products do?
Cl2 + 2NaOH -> NaCl + NaClO + H2O
Mixture used as bleach and to kill bacteria.
