Halogens more Flashcards
Fluorine
very pale yellow gas. Highly reactive.
Chlorine
greenish, reactive gas, poisonous in high concentration
Bromine
red liquid, that gives off dense brown/orange poisonous fumes
Iodine
shiny grey solid sublimes to purple gas
trend in melting point and boiling point
Increase down the group, molecules become larger and have more electrons and so have larger van der waal forces.
trends in electronegativity
decreases- the atomic radius increases due to the increasing number of shells. Nucleus less able to attract
Oxidising strength trend in halogens
decreases down the group
what are oxidising agents
Oxidising agents are electron acceptors
Chlorine with potassium chloride
Very pale green, no reaction
Chlorine with potassium bromide
yellow solution, Cl has displaced Br
Chlorine with potassium iodide
Brown solution, Cl has displaced I
Bromine with potassium chloride
Yellow so no reaction
Bromine with potassium bromide
Yellow solution, no reaction
Bromine with potassium iodide
Brown solution, Br has displaced I
What does the colour in the solution suggest
Shows which free halogen is present in solution.
Fluoride with silver nitrate
no precipitate
Chlorides with silver nitrate
white precipitate
Bromide with silver nitrate
cream precipitate
Iodide with silver nitrate
yellow precipitate
why is ammonia used ?
to differentiate between the halides if the colours look similiar
does silver chloride dissolves in dilute ammonia
yes
does silver bromide dissolve in dilute ammonia
no, but yes in concentrated ammonia
Does silver iodide dissolve in ammonia
no, not even in concentrated ammonia
Reaction of halide salts with concentrated sulphuric acid: fluoride and chloride
Not strong enough reducing agents to reduce the S in H2SO4- ONLY ACID BASE reactions occurNaF + H2SO4 –> NaHSO4 + HbrWHITE STEAMY FUMES OF HCL ARE INVOLVED
Reaction of halide salts with concentrated sulphuric acid: With Bromide
two steps: acid base step (initially reduces sulfur) and redox step Acid base step: NaBr + H2SO4 –> NaHSO4 + HFRedox step: 2HBr +H2SO4 –> Br2 + SO2 + 2H2O.White steamy fumes of HBr are evolved. Red fumes of Bromine are also involved and a colourless, acidic gas SO2H2SO4 acts as acid in first step to produce HBr and is an oxidising agent
Reaction of halide salts with concentrated sulphuric acid : With Iodide
Strongest reducing agent- reduce sulfure from +6 to +4 in SO2 and from 0 to -2 in H2SWhite steamy fumes of HI involved. Black solid and purple fumes of idone are also involved. Colourless, acidic gas SO2, yellow solid of sulfur, H2S a gas with a bad egg smell
Reaction of halide salts with concentrated sulphuric acid: 4 steps of Iodide
NAI + H2SO4 –> NaHSO4 + HI2HI + H2SO4 –> I2 + SO2 +2H2O2HI + H2SO4 –> 3I2 + S + 4H2O8HI + H2SO4 –> 4I2 + H2S + 4H20
DISPROPORTIONATION
The name for a reaction where an element simultaneously oxidises and reduces
Chlorine with cold water
Cl2 + H2O –> HOCL +HCL- Chlorine is simultaneously reducing and oxidising
Chlorine with water in sunlight
2Cl2 + 2H2O –> 4H+ + 4CL + O2
Reactio of chlorine with cold dilute NaOH
Cl2 + 2NaCl –> NaCl +NaOCl + H2O
Uses of chlorine
kills bacteria in pools and used as bleach
why can we use chlorine in pools
Used in sufficiently small amounts and the benefits to health of water treatment outweigh its toxic effect
Halogens are used to make halogenated organic compounds.The refrigerant used in air conditioners is a mixture of fluorinated alkanes.These compounds are made by fluorination reactions.The mechanism for the reaction of fluorine with an alkane or with a fluoroalkane is a free-radical substitution similar to the reaction of chlorine with methane.Write the overall equation for the reaction of fluorine with methane to form trifluoromethane (CHF3).
CH4 + 3F2—————> CHF3 + 3HF
Write equations for the following steps in the mechanism for the reaction of fluorine with trifluoromethane (CHF3) to form tetrafluoromethane (CF4).Initiation step………………………………………………………………………………………………………………………….. First propagation step………………………………………………………………………………………………………………………….. Second propagation step………………………………………………………………………………………………………………………….. A termination step leading to the formation of hexafluoroethane
InitiationF2 —->2F•First propagationF• + CF3 —-> •CF3 +HFSecond propagationF2 + •CF3 —->CF4 + F•Termination (must make C2F6)2 •CF3 —-> C2F6 or CF3CF3
Identify a bond in a CFC that is broken by ultra-violet radiation to produce a reactive intermediate.Give the name of this reactive intermediate that catalyses the decomposition of ozone. Write an overall equation for this decomposition of ozone.Bond broken ……………………………………………………………………………………………………….. Name of the reactive intermediate ………………………………………………………………………….Overall equation
*C―Cl bond OR carbon-chlorine bond chlorine atom OR chlorine (free) radical 2O3 —-> 3O2
When silver nitrate solution is added to a mixture containing two different halide ions in solution, two different precipitates, R and S, are formed. When concentrated ammonia solution is then added, R remains as a precipitate and S dissolves completely.Identify the halide ion in RIdentify a possible halide ion in SWrite an ionic equation for the formation of the precipitate R from silver nitrate
I-Cl- or Br-Ag+ + I− ——->AgI
When concentrated sulphuric acid is added to solid sodium chloride a reaction occurs in which misty fumes are formed.Write an equation for this reactionState the role of sulphuric acid in this reaction.
H2SO4 + NaCl——->NaHSO4 + HClAcid
When concentrated sulphuric acid is added to solid sodium bromide, a redox reaction occurs. A mixture of gases, including sulphur dioxide, is formed.State the oxidation state of sulphur in sulphuric acid and in sulphur dioxide.Oxidation state of sulphur in sulphuric acid …………………………………………………..Oxidation state of sulphur in sulphur dioxide
(+) 6; (+) 4;
Write an equation for the redox reaction between concentrated sulphuric acid and solid sodium bromide. State the role of sulphuric acid in this reaction.Equation Role of sulphuric acid .
H2SO4+2H+ +2Br− ——–> Br2 +SO2 +2H2O; Oxidising agent / electron acceptor;
When concentrated sulphuric acid is added to solid sodium iodide a redox reaction occurs to produce sulphur dioxide. Two other reduction products are formed.Identify these two other reduction products. In each case, state an observation that would confirm the identity of the product.Reduction product 1 ObservationReduction product 2 Observation
Hydrogen sulphide; Bad egg smell; Sulphur;Yellow solid
State and explain the effect on the rate of a reaction involving gases when the volume of the container is decreased but the number of gas particles and the temperature stay the same (3)Effect Explanation
IncreasesMore collisions; Particles closer together / greater concentration / increased pressure;
Give one reason why a metal catalyst is often used in the form of a gauze or a powder.
Greater surface area making more collisons possible
State and explain the effect on the equilibrium yield of a reaction when a catalyst is used.Effect on equilibrium yield Explanation
No effectRate of forward and backward reaction increased equally
