Elements Of The Sea Flashcards
What is the atom economy equation
Mr useful products / Mr useful reactants x 100
When is the big number in an equation used
In atom economy
How do you find molecular formula
Find empirical formula
Add atomic masses in the empirical
Add the Mr for molecule divide by mass of atoms (empirical)
Times the molecule by this
What is redox
Reaction where reduction and oxidation take place
How can you tell if a molecule has been reduced/oxidised in a redox reaction
By oxidation states, transfer of electrons
Oxidation is an increase in oxidation state - lost electrons
Reduction is a decrease in oxidation state - gain electrons
What is the oxidation number of an uncombined element
0
What is the oxidation number of ions
What the ion charge is e.g NO3^- would be -1
What is the oxidation number of fluorine
Always -1
What is the oxidation number of oxygen
In all compounds -2, except peroxides -1 of combined with fluorine +2
What is the oxidation number of hydrogen
In all compounds +1 except metal hydrides -1
What is the oxidation number of chlorine
-1 except when with oxygen and fluorine, need to work it out
What is the oxidation number of group 1 and 2 metals
Group 1 is +1
Group 2 is +2
How do you find the oxidation number of a element in a compound
e.g CO3^-2 O=-2 C + (-2 x3) = -2 C - 6 = -2 C = 14
What is disproportionation
Same element in one reaction gets oxidised and reduced
What always occurs at the anode
Oxidation
What always occurs at the cathode
Reduction
What is the ionic equation for brine electrolysis
2Cl^- + 2H2O -> Cl2 + H2 + 2OH^-
What is the half equation of brine electrolysis at the anode
2Cl^- (aq) -> Cl2 (g) + 2e^-
What is the half equation of brine electrolysis at the cathode
2H^+ (aq) + 2e^- -> H2 (g)
What occurs in molten electrolysis
Solid ionic compounds don’t conduct electricity as ions in solid not free move
Ionic compound melted, charged ions in solid not free move, carry current
In molten electrolysis, cathode makes metal and anode makes non-meta, (except hydrogen)
What happens in solution electrolysis
Easier than molten
Dissolved ionic compound, ions free can carry current
Water compete with ions from salt
What can be made at the cathode
Hydrogen if metal is stronger than hydrogen - group 1/2 or is Al
Metal for all other salts
Hydrogen made on acid electrolysis
What can be made at the anode
Halogen if salt is a halide
Oxygen if salt is sulfate/nitrate
Oxygen if hydroxide electrolysis
How do you balance a redox reaction
- Balance atoms
- Balances charges using oxidation states (including moles)
- Multiply the opposite charge to opposite atom
How do you nomenclature (name) using oxidation states
Use oxidation states to work out the other element in compound e.g Ni(NO3)2 x1 Ni^2+ x2 NO3^- O = -2 x 3 = -1 N = -6 = -1 N = 5 Nickel Nitrate (V)
What are iodine-sodium thiosulfate titrations used for
Help find concentration of oxidising agent
More concentrated oxidising agent is, more ions oxidised by certain volume of it
How do you find the concentration of potassium iodate (V) KIO3
IO3^- (aq) + 5I^- (aq) + 6H^+ -> 3I2 (aq) + 3H2O (l)
Use oxidising agent to oxidise as much iodide as can, measure certain volume e.g 25cm^3 of KIO3. Add excess KI to solution. Iodate (V) ions in KIO3 solution oxidise some iodide ions to iodine
2. Find amount iodine moles made by titrating (use starch indicator to detect iodine -> black) make sodium thiosulfate
I2 (aq) + 2S2O3^2- (aq) -> 2I ^- (aq) + S4O6^2- (aq)
Iodine fully reacts with 11.1cm^3 of 0.120moldm^-3 thiosulfate
Moles = 0.120x11.1/1000 = 1.332x10^-3mol
3. Oxidising agent concentration (use original equation) = 2.22x10^-4x1000/25.0 = 8.88x10^-3moldm^-3
How can you make a titration accurate
Use burette
Do rinsings
Do repeats
What are the problems with iodine-sodium thiosulfate titrations
Solutions used react very slow with oxygen in air
If add starch solution too soon, iodine ‘stick’ to it so won’t react, unreliable, only add when pale yellow
What form of compound is a halogen always in
Always combined and exist as diatomic molecules e.g Cl2
Why don’t halogens dissolve in water
They’re non-polar
Why are all halogens volatile
Weak attractive forces between molecules
What occurs to the melting/boiling points down halogens
Down group id-id bonds stronger gets bigger so increase down group as molecules larger (more electrons) stronger intermolecular forces
What is fluorine at room temperature
Play yellow gas
What is chlorine at room temperature
Green gas
What is bromine at room temperature
Dark red volatile liquid
What is iodine at room temperature
Shiny black solid
Sublime, purple vapour
What are the isotopes and percentage abundances of fluorine
19F = 100%
What are the isotopes and percentage abundances of chlorine
35Cl = 75% 37Cl = 25%
What are the isotopes and percentage abundances of bromine
79Br = 50% 81Br = 50%
What are the isotopes and percentage abundances of iodine
127I = 100%
How does the water solubility change in the halogens
Decreases down the halogens group
What are halogens more soluble in
Organic solvents
What colour is chloride in cyclohexane and water
Cyclohexane - pale green
Water - almost colourless
What colour is bromide in cyclohexane and water
Cyclohexane - red/orange
Water - yellow
What colour is iodine in cyclohexane and water
Cyclohexane - violet
Water - brown
Why are halogens good oxidising agents
Halogens tend to remove and election from others to form full outer shell, all oxidising agents
Which is the best oxidising agent that’s a halogen
Fluorine most reactive and strongest oxidising agent
How does oxidising agent change down halogens
Down group less effective oxidising agents (worse at gaining electron) greater distance between nucleus and outer shell (atoms bigger), more shielding so electrons less attracted
What happens in a halogen-halide redox reaction if add aqueous halogen solution to solution with halide ions
Only displace halides if below them on periodic table
Thing displaced is oxidised and thing that does displacing is reduced
What is the ionic equation for chlorine water (colourless) and potassium bromide solution (colourless)
Cl2 (aq) + 2Br ^- (aq) -> 2Cl^- (aq) + Br2 (aq)
What is the ionic equation for bromine water (orange) and potassium iodide solution (colourless)
Br2 (aq) + 2I^- (aq) -> 2Br^- (aq) + I2 (aq)
What is the ionic equation for chlorine water (colourless) and potassium iodide solution (colourless)
Cl2 (aq) + 2I^- (aq) -> 2Cl^- (aq) + I2 (aq)
What happens to bromide when displaced
Bromine formed, turns orange
What happens if iodine is displaced
Iodine formed, turns brown
Iodide oxidised 2I^- -> I2 + 2e^-
What is formed when halide ions react with silver ions, and general equation
Solid precipitate forms
Silver halide insoluble, are precipitated when solution of silver ions added to halide ions solution.
Ag^+ (aq) + X^- (aq) -> AgX(s)
What colour precipitate formed from silver chloride, and ionic equation
White
Ag^+ (aq) + Cl^- (aq) -> AgCl (s)
What colour precipitate formed from silver bromide, and ionic equation
Cream
Ag^+ (aq) + Br^- (aq) -> AgBr (s)
What colour precipitate formed from silver iodide, and ionic equation
Yellow
Ag^+ (aq) + I^- (aq) -> AgI (s)
How can you tell the difference between halide ions
Add ammonia solution
AgCl - soluble
AgBr - sparingly soluble
AgI - insoluble
Which halide ions are decomposed
Silver chloride and silver bromide both decomposed by light to make silver metal and halogen
light
e.g silver bromide -> silver + bromide
How is a large amount of HCl made as a co-product
Co-product of chlorination or organic compounds
How can hydrogen chloride be converted to hydrochloric acid
Passing through water
High concentration solution can be made easily as hydrogen chloride high water solubility
Hydrogen chloride gas made of covalent molecules - dissolved in water forms hydrated H^+ (aq) and Cl^- (aq)
What does sodium fluoride and sodium chloride form when react with concentrated sulfur if acid
Make hydrogen fluoride/chloride gas
See white fumes of hydrogen chloride as meets moist air
Tiny hydrochloric axis droplets made
What forms when sodium bromide reacts with concentrated sulfuric acid
Hydrogen bromide
Bromide ions not strong enough reducing agent to reduce sulfuric acid to sulfur dioxide
Why is adding concentrated sulfuric acid to sodium bromide not an efficient way of making hydrogen bromide
Not pure is a mix of hydrogen bromide, sulfur dioxide and bromine vapour
What forms when sodium iodide reacts with concentrated sulfuric acid
Hydrogen iodide
As strong enough reducing agent do sulfuric acid reduces further into hydrogen sulfide gas
Why is adding concentrated sulfuric acid to sodium iodide not a good way to make hydrogen iodide gas
Not pure, gas made will be mix of hydrogen iodide (white flumes) and hydrogen sulfide
How can you make pure hydrogen bromide/iodide
Use concentrated phosphoric acid, isn’t reduced, so pure hydrogen halide
What happens to the thermal stability down group 7 halogens
Down group decreases in thermal stability as down group increase outer shells. Hydrogen fluoride has the strongest covalent bond as shortest bond
What happens what hydrogen fluoride is heated
Not broken down
What happens to hydrogen chloride when heated
Not broken down
What happens to hydrogen bromide when heated
Some brown bromide gas made when strongly heated
What happens to hydrogen iodide when heated
Lots purple gaseous iodide made if red hit needle plunged into hydrogen iodide
Which is the least acidic hydrogen halide
All acidic except hydrogen fluoride, not strongly
What percentage of dissociation occurs and which hydrogen halides
100%
HCl, HBr, HI
What ion does all acidic solution contain
H^+ (aq) ions, shown as oxonium ion H3O^+ (aq)
HCl + H2O -> H3O^- (aq) + Cl^- (aq)
What do hydrogen halides react with to make salts, what is the experiment
Ammonia
Glass rod dipped in concentrated ammonia solution placed in hydrogen halide, white cloud given of ammonium halide made
NH3 + HCl -> NH4^+ + Cl^-
Why do hydrogen halide reactions differ with concentrated sulfuric acid
Increasing strength of halide ions as reducing agents, solid halides with sulfuric acid
What forms when hydrogen fluoride/chloride reacts with sulfuric acid
No reaction
What forms when hydrogen bromide reacts with concentrated sulfuric acid
Makes sulfur dioxide
What forms when hydrogen iodide reacts with concentrated sulfuric acid
Makes hydrogen sulfide
What can happen if exposed to chlorine gas in small dose
Irritate eyes, skin, respiratory system
What happens if inhale chlorine concentrations of 40ppm+
Reacts in lungs form hydrochloric acids, affect lung tissue and causes drowning as liquid floods lungs
How is chlorine transported if not made at site
By road or rail in specially designed pressurised tank containers
What may be on a lorry or on the tank carrying chlorine
Hazchem warning plate attached to tank when transported incase fire brigade need information
How is chlorine transported and what happens if the temperature or pressure gets too high i
Liquid as more can be stored than gas under pressure
If too high pressure or temperature tanks have pressure release devices designed to vent tank, realise some gas
What are tanks usually lined with, and why must inside the tank be dry
Steel
As chlorine reacts with water to produce corrosive acids
What happens if there is too much liquid discharge
Large chlorine tanks is excess flow valve, designed to close automatically if angle valve which regulates discharge of liquid chlorine at exit port exceeds some predetermined value
Why is a scrubber unit used when transferring from rail tanker to bulk trailer on site
Scrubber unit ensures air being displaced from bulk trailer has chlorine removed
What is on the scrubber that is used to remove chlorine
Has sodium hydroxide solution, reacts with chlorine makes sodium chlorate (I) - bleach which is sold on
How is chlorine stored and moved
In cylinders
Use hoist to move them avoiding damage
How do they check stored cylinders
Take stick soaked in concentrated ammonia solution over end if leaking white cloud of ammonium chloride seen
What are the uses of chlorine
Water treatment, kill bacteria and other pathogens, chlorination of water decrease in typhoid
Household bleach products, kills bacteria, remove stains from clothes
How does bleach remove stains from clothes
Is oxidising agent so removed stains by breaking bonds in coloured chemicals to form colourless products
What is equilibrium
Reaction can go forward and backward
Rates are equal
Concentration of reactants and products stay same
What condition does an equilibrium reaction have to be under and why
Closed system so that nothing goes in or out
Why aren’t high pressures used
Too expensive to obtain and the equipment is expensive
What is the equilibrium constant
Kc
aA + bB cC + dD
Kc = [products]/[reactants]
How does the concentration affect Kc
Equilibrium shifts to try keep reactants and products same
Kc unchanged
What affects Kc
Temperature always
Pressure if it is a gas
What is Le Chatelier’s principle
If a system (reactant and product chemicals) at equilibrium and change made in any of conditions then the system will oppose change
How do catalyst affect equilibrium
No effect as only speed up rate of both reactions
Reduces time for equilibrium to be reache d
How does pressure affect equilibria
The amount of moles on each side
e.g if increasing pressure, shifts equilibrium to side with fewer gas molecules, reduces pressure
