TOPIC 5- separate chemistry 1 Flashcards
Where are transition metals positioned in the periodic table?
Right in the middle (between group 2 and 3)
Properties of transition metals
Similar to that of typical metals
Hard, strong, shiny, sonorous, malleable, heat/electricity conductors, high melting points, high densities.
Good catalysts
V colourful
Examples of transition metals used as catalysts
Iron is used in the Haber process to make ammonia.
Vanadium pentoxide is used in the Contact process to make sulfuric acid.
Densities of transition metals
High densities
In general, transition metals have higher densities than group 1 metals.
How are alloys stronger?
Pure metals regular arrangement enables the layers of ions to slide over each other. However alloys have different sized atoms so layers can’t slide over each other as easily.
Alloys of iron
Steels
Made by adding carbon to pure iron.
Or stainless steel is made by adding chromium and nickel.
Strength of steel
Harder than iron and stronger (as long as carbon percentage doesn’t exceed 1%.
Is less corrosive
Bronze
Copper + tin
Harder than copper, used to make medals, decorative ornaments and statues.
Brass
Copper + zinc
More malleable, used when less friction is required
Water taps and door fittings
Gold alloys
Harder than pure, soft, malleable gold. 1 carat (1/24)
Aluminium alloys
Aluminium has a low density but isn’t strong enough for aeroplanes.
Allowed to increase strength
Magnalium
Aluminium + magnesium
Stronger, lighter and corrodes less easily than pure aluminium. Makes parts for cars and aeroplanes.
High magnesium content is used in fireworks as burns brightly.
Corrosion
Metals reacting with oxygen to form metal oxides in the presence of oxygen and water.
What type of reaction is corrosion?
How ?
Redox reaction
Metal loses electrons (oxidised)
Oxygen gains electrons (reduced)
Rusting
Corrosion of iron
Occurs when iron is in contact w oxygen and water.
Experiment to show both oxygen and water are needed for iron to rust
Put iron nail in boiling tube w just water (boiled before to remove oxygen and oil to stop oxygen getting in) > won’t rust
Put iron nail in tube w just air (calcium chloride absorbs any water from air) > won’t rust
Our iron nail in boiling tube of water and oxygen > will rust
2 methods to prevent rusting
Barrier
Sacrificial
Barrier methods to prevent rusting
Painting
Oiling/greasing (particularly w moving parts)
Sacrificial protection methods to prevent rusting
Galvanising (coat of zinc on iron object, more reactive)
Electroplating
Electroplating
How is it carried out?
Coating the surface of a metal with another metal using electrolysis.
Cathode (object you what electroplated)
Electrolyte (solution w ions of the metal you’re plating)
Anode (metal you what to electroplate w)
What are titrations used for?
Allow you to find out exact amount of acid needed to neutralise given quantity of alkali.
How do you carry out a titration?
Use a pipette to measure out a set volume of alkali into a flask w a few drops of indicator (phenolphthalein/methyl orange).
Fill a burette w standard solution of acid. Add acid to alkali little at a time and mix regularly, going slower when you think it’s close to neutralisation.
(Can use rough titration first).
Indicator changes colour when is neutralised, record volume needed.
Repeat to receive similar results and take mean.
Why can’t you use a universal indicator in titrations?
Because you want a single colour change and universal indicator changes colour gradually.
Safety precautions in titrations
Keep burette below eye level while you fill it so no acid gets in your eyes.
What colour does phenolphthalein turn?
Pink in alkali
Colourless in acids
What color does methyl orange turn?
Yellow in alkalis and red in acids.
Concentration formula
Number of moles (mol)/ volume of solution (dm cubed)
How do you convert from g dm cubed to moles dm cubed?
Divide by Mr
Yield
The amount of product you get from a reaction
Percentage yield formula
Actual yield/ theoretical yield *100
Why is it very rare to get a 100% yield?
INCOMPLETE REACTIONS (not all reactants are converted to products) PRACTICAL LOSSES (reactants leftover in containers) UNWANTED REACTIONS (caused by impurities in reactants/change in reaction conditions)
Atom economy
Percentage of mass of reactants converted to useful, desired product when manufacturing a chemical.
Formula for atom economy
Total Mr of desired products/ total Mr of all products * 100
Method to work out atom economy
1 identify delisted product
2 work out total Mr of all products
Work out total Mr of desired products
Calculate w formula
Disadvantages of low atom economy
Unsustainable environmentally as use up resources v quickly, producing much waste to be disposed of.
Unprofitable as raw materials can be expensive to buy and waste products can be expensive to dispose of.
How to tackle high waste production
Find a use for waste (not throwing away).
Use a reaction producing more useful by-products.
Factors to consider in chemical industry
Percentage yield (higher yield:))
Atom economy
Reaction rate (fast enough).
Equilibrium positions in reversible reactions.
When designing industrial processes, factors to consider
Cost of extraction and refining (economically viable?)
Energy costs
Control of conditions (maximising yield at acceptable rate)
Haber process reaction
N2(g) + 3H2 (g)>< (reversible sign) 2NH3(g) (+ heat)
Pressure of Haber process
High pressures favour forwards reaction.
(More moles on left)
200 ATMOSPHERES
(High pressure that’s not too expensive to ensure)
Temperature of haber process
Low temperature as reaction is exothermic.
450°C (compromise between maximum yield and rate of reaction).
Catalyst in Haber process
Iron catalyst
3 essential elements for fertilisers
Nitrogen
Phosphorus
Potassium
Function of fertilisers
Supply elements needed for growth and life processes that may be missing from the soil to increase crop yield, causing p,ants to grow bigger and faster.
Ammonia fertiliser advantages over traditional fertilisers (eg manure)
Ammonia fertilisers are soluble so chemicals dissolve down into soil to reach plants.
Chemical compositions can be controlled.
Ammonia reactions
Can be reacted w water and oxygen to produce nitric acid.
Can be reacted w acids to form ammonium salts.
Production of soluble salts (ammonium sulfate)
NEUTRALISATION REACTION w titration
Add methyl orange to ammonia (yellow as is alkali).
Slowly add sulphuric acid w burette until yellow turn red, stirring constantly, slow as reach end.
Note down titration and redo without methyl orange as it then is impure.
How do you get solid ammonium sulphate crystals from an ammonium sulphate solution?
Evaporate w a steam bath and leave to crystallise.
Why are titrations not used in industry to make fertilisers?
Impractical w larger quantities.
Crystallisation is v slow.
One industrial method uses large reaction chamber of ammonia gas which reacts w sulfuric acid to produce ammonium sulfate powder.
Molar volume
Units?
The volume occupied by one mole of gas.
Dm^3 per mole
Molar volume formula
Gas volume / number of moles
Avogadro’s law
Under the same conditions, the same number of moles of different gases all occupy the same volume.
1 MOLE OF ANY GAS OCCUPIES 24DM^3 AT ROOM TEMP AND PRESSURE
Chemical cells
Cells producing a voltage until all of one of the reactants is used up.
Fuel cell
A type of chemical cell supplied w a fuel and oxygen, using energy from the reaction to produce efficient electrical energy.
Hydrogen oxygen fuel cells
Hydrogen and oxygen react to produce a voltage w no pollutants, just water.
2H2 + O2 > 2H2O
Advantages of hydrogen oxygen fuel cells
More efficient than power stations or batteries
Electricity generated directly from reaction
No energy lost via heat or friction
No pollutants e.g. greenhouse gases nitrous oxide sulphur dioxide or carbon monoxide
Negative’s of hydrogen oxygen fuel cells
Hydrogen takes up much space to store
Very explosive and therefore dangerous, need pressurised tank to store
Hydrogen is supplied by either hydrocarbons or electrolysis of water which both use energy
