Topic 5- Separate chem I Flashcards
What is corrosion ?
- when a metal oxidises – usually given to iron or steel
- example of redox reaction
How to prevent rusting?
- painting -same as oil or grease
- oil or grease - forms protective coat around metal
- coating w/ plastic
How does galvanising iron protect it from corrosion
- zinc more reactive than iron so reacts instead of iron
How does sacrificial protection protect iron from corrosion
- more reactive metal connected to iron, so corrodes instead
How does tin plating iron protect it from corrosion
- tin coat protects iron underneath
- less reactive, so acts as barrier – if tin scratched iron will rust
- quite cheap
How does alloying iron protect it from corrosion
- other elements increase corrosion resistance
Percentage yield equation
percentage yield = yield obtained/ predicted yield x 100 (for percentage)
What is the yield of a reaction?
- amount of chemicals produced during during a reaction
Why does aluminium seem to not corrode?
- When corrodes forms protective layer of aluminium oxide – happens very quickly – when scratched will form layer again
- layer doesn’t allow air or water to pass through
What is atom economy?
- amount of atoms wasted or lost when a chemical is made
atom economy equation
atom economy = mass of atoms in desired product/ total mass of all products x100 – for percentage
What is electroplating?
- acts as barrier to oxygen and water
- can electroplate a metal with an unreactive
metal that is more attractive and will not corrode e.g. gold - it’s done using the metal to be plated as cathode and metal you’re plating it with is the anode
What is an alloy?
-a mixture of a metal w/ one or more other elements
How does an alloy increase the strength of a product?
- have + ions of different metals, that have different sized ions– disrupts regular structure and stops ions being able to slide as easily, so leaves much
harder, stronger metal.
Why iron alloyed to make steel
- steals mixture of carbon and iron
- Low-carbon steels are malleable so used for sheeting
- High carbon steels are hard - used for cutting tools
- Stainless steels w/ chromium and nickel are resistant to corrosion - used for cutlery
Uses of aluminium
low density, used for aircraft
uses of copper
good conductor, used in electrical cables
uses of gold
good resistance to corrosion, used in jewellery
uses of magnalium
(aluminium + magnesium): low density, used in cars and planes
uses of brass
(copper + zinc): hard, resistant to corrosion, used in coins
calculate concentration (mol dm^-3)
concentration = no. of moles (mol) / volume (dm^3)
Percentage yield equation
percentage yield = yield obtained/ predicted yield x 100
What causes the actual yield being less than the predicted yield
- incomplete reactions
- practical losses during the experiment
- side reactions
What is atom economy?
- amount of starting materials that end up as useful products
atom economy equation
Relative molecular mass of desired product from reaction / sum of molecular mass (Mr) of all reactants
Volume of gas at room temp. ( dm^3)
mol. x 24
What is Avogadro’s law
one mole of a substance contains 6.02 x 10^23 particles
- so if you had 10 moles of a substance, you’d do 10 x 6.02 x 10^23
Benefits of atom economy
- Efficient processes have high atom economies, and are important for sustainable development, they use fewer natural resources and create less waste.
What is the Haber process ?
- a reversible reaction between nitrogen
and hydrogen to form ammonia using an iron catalyst at high temperature and pressure. - 200 atmospheres
- 450 degrees temp.
When is equilibrium reached at a faster rate
- higher temp. is used (particles have more kinetic energy so collide more frequently so have more successful collisions)
- higher pressure/concentration is used (more particles in a given volume, so more frequent successful collisions)
- catalyst is used - speed up rate of reaction
How is the Haber process affected by cost of raw materials and other external factors
- a higher temp. shifts equilibrium towards the reactants forwards reaction is exothermic,compromise required
to create a fast rate of reaction and a high yield of products - Catalyst can be expensive
- High temp. and pressures can be expensive and dangerous and equipment required for them can be very
expensive
Describe how the Haber process works
- the purified gases (nitrogen and hydrogen) are passed over iron catalyst at high temp. (about 450 °C) and high pressure (about 200 atmospheres).
- reaction mixture is then cooled and condensed into liquid and is used in fertilisers (fertilisers can contain nitrogen, phosphorus and potassium)
How does ammonia react with nitric acid
-ammonia acts as a base
ammonia + nitric acid -> ammonium nitrate
- NH3 + HNO3 → NH4NO3
production of ammonium sulphate in the industry
- reactants:are natural gas, air, water (to make ammonia) and sulphur, air, water (to make sulfuric acid)
- on a large scale
- are many stages required
production of ammonium sulphate in a lab
- reactants are ammonia solution and dilute sulfuric acid (bought from chemical manufacturers)
- on a small scale
- involves a few stages
describe what happens in a hydrogen-oxygen fuel cell
- Supplied by hydrogen and oxygen (or air)
- reaction takes place within the fuel cell to produce a potential difference
- Overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water
o 2H2 + O2 → 2H2O
strengths of a fuel cell
- produce only water as waste
-keep producing fuel if fuel keeps being
supplied
weaknesses of a fuel cell
- expensive to make
- difficult to transport/store hydrogen so aren’t suitable for portable devices
What happens during a chemical cell
- chemical cells produce a voltage until one of the
reactants is used up - Chemical reactions stop when one of the reactants has been used up
