C5 + C6.1 (Acidents Happen :( ) Flashcards
What is the yield
The mass of a product made in a chemical reaction
What is theoretical yield
The maximum mass it is possible to make from the given reactants
How do you calculate theoretical yield
Find the moles in your equation and multiply the moles of your product by its mr
What is actual yield
The mass of a product that you actually make in a chemical reaction (usually less than theoretical yield)
How do you calculate percentage yield
(Actual yield ÷ theoretical yield) ×100
What range can percentage yield be between
0% and 100%
What affects percentage yield
If the reactants react in different than expected ways
The reaction may not go to completion - some of the reactants do not react
(Common in reversible reactions)
Some products may be lost when separated from the mixture to be purified
What is atom economy
A measure of how many atoms in the reactants form a desired product
If there is one product the atom economy would be 100%
How do you calculate atom economy
(total mass of desired product ÷ mass of reactants) ×100
What is a reaction pathway
Multiple reactions you can choose to create a desired product - with some being more efficient
What factors effects which reaction pathway you use
Yield of product
Atom economy of the reaction
Usefulness or otherwise, of by-products
Rate of reaction
Equilibrium position, if a reversible reaction
Cost
Environmental factors
What are by-products
Additional products made during your reaction - not the one you intended to make
How do you convert cm^3 to dm^3
Divide the cm value by 1000
What two ways can you calculate the concentration of a soluton. - g/dm^3 and mol/dm^3
Concentration = mass ÷ volume
Concentration = moles ÷ volume
C =n/v
What is a titration
A method in which a neutralisation reaction is used to determine the concentration of an acid or alkali
What are concordant results
Results within 0.1 of each other
What is a meniscus
The curve in the surface of a liquid
How do you set up a titration experiment
Use a volumetric pipette to measure out 25cm^3 of your alkali solution and put it into a conical flask
Attach you burette vertically to ensure accurate readings (preventing parallax error)
When you have filled the burette - by pouring the acid through a filter cone (25cm^3 of acid) - add indicator (2-3 drops) to your alkali
What safety equipment is needed for titrations
Safety gogles
How do you do a titration (once set up)
First take an initial burette reading, from the bottom of the meniscus and release the tap, whilst swirling the flask, until you see the indicator change colour.
Record the final reading and use them to find the total acid used.
This is your rough titration
Re-fill the burette and repeat for a more accurate titration. This time release the acid to a few cm^3 before the final value of your rough titration and slowly release the drops. Repeat this step and use your concordant results to calculate the mean titre used
You must have at least two concordant titres
How can you use results from your titration
You can use them to calculate the concentration, often in mol/dm^3
This is because you know the concentration of one liquid and the liquids used. By using the volume and the mol of your substance you can calculate the concentration
- find the mol of your known concentration
- use a balance equation to find the mol of your second liquid
Use c=m/v to find the concentration
What is molar volume
The volume occupied by one mole of a gas
24dm^3
How can you use molar volume to calculate gasses volume
Volume (dm^3) = mol × molar volume
What two things can you calculate with molar volume (gases)
The volume of a gaseous reactant or product (if you know the amount)
The amount of a gaseous reactant or product if you know the volume
What is the rate of reaction
A measure of how quickly reactants are used or products are formed
How is gas measured
Using a gas syringe
As the syringe fills, the plunger moves outwards and you can record the gas it contains (cm^3).
How does temperature affect rate of reaction.
↑temp = ↑average ke of particles
This means there are more frequent successful colisions
Increase of 10°C
Ror doubles
What is needed for a reaction to happen
If reactant particles collide
The colliding particles have enough energy to react
How can you use reaction time
Reaction time is inversely proportional to rate of reaction
Therefore by using 1/reaction time you can calculate the rate of reaction
Why are reactions faster at higher concentrations / pressure
The particles are more crowded, so there are more frequent successful collisions
How does surface area to volume ratio effect the rate of reaction (e.g as a powder)
If the surface area is greater :
More reactant particles are available for collisions
More successful collisions can occur more frequently
What is a catalyst
A substance that increases the rate of reaction without being used up
How do catalysts increase rate of reaction
They speed up the reaction by reducing the activation energy
What is collision theory
The theory that reactions can only take place when particles collide with enough energy (activation energy)
What happens to the rate of reaction, when temperature increases by 10°C
The rate of reaction will double
What is activation energy
The minimum energy needed for particles collide successfully
What is a reversible reaction
A reaction where the products can react together to form the reactants
What are the two types of reaction in reversible reactions
Forward reactions and backwards reactions
If the forward reaction is exothermic what type of reaction is the backwards reaction
It is endothermic
What is needed for a reversible reaction to be in equillibrium
It needs to be in a closed system (e.g a covered flask)
What is dynamic equillibrium
When a reversible reaction is at equilibrium, the rate of forward and backward reactions are equal
As these reactions are happening simultainiously it is a dynamic equillibrium
How do the concentrations of substances change in dynamic equillibrium
The concentrations remain constant
What is the equilibrium position
A description of the relative amounts of reactants and products in a mixture at equillibrium
Where is the equilibrium position when the reactants concentration is greater than the products
To the left
Where is the equilibrium position when the reactants concentration is lower than the products
To the right
What happens to the equillibrium position if you change the concentration of a substance in equillibrium
The equilibrium position moves away from the substance you have increased in concentration
What happens to the equillibrium position if you change the presure of a system in equillibrium
Pressure ↑ = moves in the direction of the fewest moles of gas
What happens to the equillibrium position if you change the temperature of a system in equillibrium
The equilibrium position moves in the direction of the endothermic change
What is La chatliers principle
If a system at equilibrium is exposed to a stress the system will shift to reduce that stress
Describe what happens if you increase the concentration of A
A→←B
(Reversible reaction)
The reaction becomes unbalanced so the forward reaction will speed up to use up the reactants
The equilibrium has been shifted to the right, to produce more products
Why does the equilibrium position change
As the reaction always wants to be in equilibrium, so it has to change to make the rate of reaction equal
How do you choose suitable pressures for a reaction
Using a high pressure for some reactions can speed up the rate of reaction
However working at pressures too high is expensive and can be dangerous
How are temperatures chosen for reactions
Specific temperatures are chosen based off of whether the reaction is endo or exothermic.
However s temperature cannot be too low as that will reduce the rate of reaction
What is the harber process
A process to manufacture ammonia from nitrogen and hydrogen
N2 + 3H2 →← 2NH3(g)
How are the raw materials for the harber process manufactured
Nitrogen → fractional distillation of liquified air
Hydrogen → reacting with a natural gas such as methane, with steam
What are fertilisers
Substances that replace mineral ions used by plants when the grow
What are npk fertilisers / what ion do the replace in the soil
Nitrogen → nitrate or ammonium ions
Phosphorus → phosphate ions
Potassium → potassium ions
What are the ideal conditions for the harber process
200 atmospheres (200Mpa)
Temperature of 450°C
An iron catalyst
What happens to unreactive nitrogen and hydrogen in the harber process
It is used again (put back into the chamber used)
How does the temperature effect, yield rate of reaction and cost for the harber process
↓ yield (forward reaction is exothermic)
↑ rate (more frequent successful collisions)
↑ cost (energy cost increases)
How does the pressure effect, yield rate of reaction and cost for the harber process
↑ yield (less mol ok the right of the equation)
↑ rate (more frequent successful collisions)
↑ cost (energy costs)
How does the catalyst effect, yield rate of reaction and cost for the harber process
No change in yield
↑ rate (lowers activation energy)
↑ cost (cost of catalyst is relatively cheap)
What are organic fertilisers
Fertilisers made from fish bones or manure
What happens to a plant with a nitrogen deficiency
Poor growth + yellow leaves
What happens to a plant with a phosphorous deficiency
Poor root growth, discoloured leaves
What happens to a plant with a potassium deficiency
Poor fruit growth, discoloured leaves
How are fertilisers made
By neutralising an acid
Acid + alkali → salt + water
The salt is the fertiliser
Once neutralised used crystallization to obtain the salt
Why are fertilisers made through a continuous process
Allows for automated production
More can be sold
What is the contact process
A method used for making sulfuric acid
What happens in the contact process
Stage 1
Sulfur is burnt in air to produce sulfur dioxide
S + 02 → 2SO2
Stage 2
Sulfur dioxide and oxygen react to produce sulfur trioxide
2SO2 + O2 →← 2SO3
Stage 3
The sulfur trioxide is converted to sulfuric acid
H20 + SO3 → H2SO4
(This is done in two different ways, as this reaction releases harmful gases)
What are the conditions chosen for stage 2 of the contact process
Pressure of two atmospheres (200Kpa)
Temperature of 450°C
vanadium V oxide catalyst (V2O5)
How are the hazards in the contact process controlled
In stage 3 the reaction is very exothermic and produces a hazardous mist so it is carried out in two steps
H2SO4 + SO3 → H2S2O7
(Sulfuric acid + sulfur trioxide previously → oleum)
H2S2O7 + H2Ob→ 2H2SO4
(Oleum + water → concentrated sulfuric acid)
Why is ethanol made in two different ways
Fermentation of ethanol has a lower yield but can be drunk
Hydration of ethanol has a higher yield but cant be drunk
How is ethanol made through fermentation
A crop is turned into glucose and added to yeast
Fermentation takes place in anaerobic conditions and Co2 is produced as a waste product
Yeast breaks down the glucose using enzymes, so in order to work fermentation is carried out at 35°C
The ethanol also needs to be purified through distillation
How is ethanol produced through hydration
Raw materials such as crude oil are refined into ethene (fractional distillation and cracking)
Ethene is then heated with steam and a catalyst to produce ethanol
There are no waste products
It is a reversible reaction
Requires a temp of 300°C
And 60 atmospheres
What is the difference in purity of ethene made by hydration and fermentation
Fermentation - low purity (must be distilled)
Hydration - high purity (no by-products)
What is an ore
Rock or mineral containing enough metal to make it economical to use
How are ores extracted
Electrolysis is expensive and can be used to extract all ores
If the metal is less reactive than carbon cheaper methods are used
How is copper extracted from copper (II) sulfide
Copper (II) sulfide is roasted in air
Copper (II) + oxygen → Copper (II) oxide + sulfur dioxide
Stage 2
The copper (II) oxide is heated with carbon
Copper(II) oxide + carbon → copper + Carbon Dioxide
This is a redox reaction
What is coke
Product (mainly carbon) made by heating coal in the absence of air
Give an example of iron ore
Haematite
What is a blast furnace
Industrial reaction vessel for iron production
How is iron extracted
Coke, limestone (explained next flashcard) and iron(III) oxide are put into the blast furnace
Stage 1
Coke burns in hot air producing carbon dioxide
Carbon + oxygen → carbon dioxide
Stage 2
Coke reduces the carbon dioxide making carbon monoxide
Carbon + carbon dioxide → 2 carbon monoxide
Stage 3
Carbo monoxide reacts with iron (III) oxide at around 1500°C
3 CO + Fe2O3 → 3CO2 + Fe
How are impurities removed from iron
They are removed by limestone
Calcium carbonate decomposes at high temperatures
CaCO3 → CaO + Co2
The calcium oxide reacts with silica (from sand impurities) to form calcium silicate
CaO + SiO2 → CaSiO3
Calcium silicate is known as slag and floats on top of the molten oron
What is slag
Waste material.
In extracting iron, the calcium silicate is called slag
What ore contains aluminium
Bauxite (aluminium oxide)
What is aluminum used for
Making drink cans, aircraft, overhead electricity cable, window frames
How must aluminum be extracted
Through electrolysis (as it is more reactive than carbon)
How is the melting point of aluminum oxide reduced and why.
It is dissolved in cryolite reducing its temp from 2000°C to 950°C
This means less energy has to be used, saving money
How is aluminum oxide electrolysed
This is NOT electroylsis of molten m
The molten aluminum oxide dissolved in cryolite is placed in a large electrolysis cell, made from steel and lined with graphite
The graphite lining of the case acts as the cathode.
A series of graphite blocks act as the anode
Aluminum is produced at the cathode
What is the half equation for the reactions during electrolysis of aluminum oxide
Cathode
Al3 + 3e- → Al
Anode
2O2- → O2 + 4e-
Why do the anodes in an aluminum electrolysis cell have to be replaced every few weeks
As impurities from the solution and cryolite join to them
What is photomining and how is it done
Process of obtaining low grade ore
Crops are grown on soil containing low grade ore
A complexing agent is added to the soil to enhance the crops uptake of the metal
Once grown the plants are burnt to ash
The plant ash contains metal ions and is smelted to yield the metal
This process is carbon neutral, but incredibly slow as the plants take years to grow
What is a low grade ore
Rock with a low concentration of an ore
What is bioleaching / how is it done
Bacteria oxidises Iron (III) and sulfide ions.
This forms sulfuric acid which breaks down copper sulfide ores releasing copper (II) ions
Waste iron can be added to the solution to displace copper ions and produce copper
Comparison of bioleaching to photomining
Photomining:
Slow
Carbon neutral
Plants take up a large area to grow (less land for food farming)
Plants could alter the ecology
Bioleaching:
No waste products
90% of metal is extracted
Very slow process that can take gears
Uses less than 50% of the energy of traditional mining
Possible damage to the environment
What are alloys
A mixture of two or more elements
What is different between the structure of an alloy and the structure of a pure element
In a pure element the atoms are all the same size, so layers can slide over each other
In alloys there are different sized atoms, so they layers cant slide as well
This is why alloys are harder to bend
What is solder made of / used for
It is an alloy made of tin and copper
It melts at 227°C so can be used to join electrical components without damaging
If copper was used instead the electrical components would be damaged as it melts at 1085°C
What is corrosion
The reaction of a metal with substances in its surroundings, such as air and water
What is rusting
The corrosion of iron or steel
What type of reaction is corrosion
A redox reaction, as the metal reacts with oxygen (and water) in the air
Why doesnt aluminum corrode
It always forms a thin layer of aluminum oxide, when exposed to air.
This means water and oxygen cannot react with the oxygen
How does silver corrode
In the presence of hydrogen sulfide (produced naturally by bacteria)
It reacts with the silver when oxygen and water are present, producing a thin layer of black silver sulfide
What are the 4 main methods of reducing rust
Painting
Coating with oil grease or plastic
Plaiting with zinc (galvanizing)
Playing with tin
What is sacrificial protection
Rust prevention, in which a metal more reactive than iron such as magnesium or zinc, corrodes instead of iron or steel
How does coating something in plastic prevent rusting
It prevents oxygen or water from coming in contact with the metal
Where is sacrificial protection used (examples)
On ships, blocks of magnesium or zinc are played onto the hull
This protects the hull from rusting
Why is sodium not suitable for sacrificial protection
It reacts too violently with water
What is the process taken to galvanize a metal
A metal has to be dipped into molten zinc.
It is then cooled and then the thin layer of zinc solidifies
What does galvanizing do
It stops air and water reaching the metal (e.g iron or steel)
It acts as sacrificial protection, so even if the zinc layer is damaged the object is protected
How do you coat an object with tin
You have to electroplate it or dip it in molten tin
Why can tin be bad for rust prevention
If used on steel cans and it is damaged :
The steel acts as sacrificial protection instead of the tin and rusts faster
(It is less reactive than iron)
What are ceramics
Hard non-metalic materials such as brick
What is the structure of most ceramics
Combination of metals and non metals
In a giant ionic lattice, or giant covalent structure
What are the typical properties of ceramics
High melting points
Hard and stiff, not brittle
Poor conductors of electricity and heat
How is glass formed
It is made by melting sand and leaving it to cool and solidify
Unlike other ceramics it has an irregular structure without crystals making it transparent
How are most ceramics formed
By heating clay to high temperatures
Tiny crystals form joined together by glass
What properties are important to look at when choosing a material to use
Properties relevent to its purpose, e.g
Conductivity
Tensile strength
Cost
Electrical resistance
Compressive strength
What are composite materials
A material made from two or more materials with different properties to the original materials
Why are composite materials used
As they can have improved properties to original materials
E.g
Stronger
Less dense
Cheaper
Why are clothes made from a composite material
Polyester-cotton is an artificial polymer
It is made by weaving polyester and cotton fibers together
It is comfortable and harder than cotton, whilst still being easy to wash and dry
What is Resin
A substance that changes from the liquid state to a solid state due to chemical reactions
What is fiberglass made of
Glass fibers and a resin
What is concrete
A composite material made from aggregate sand and cement
What is concrete used for
It has a high compressive strength so can be used for the foundations of buildings
What is steel reinforced concrete used for
This makes the concrete have a higher tensile strength and a high compressive strength, making it better to build with
What is plywood
A composite material
Made from combining wood boards with alternating grain patterns
This increases its strength and makes it harder to bend
What is the Life Cycle assessment
Analysis of the impact, production, use and disposal of a manufactured product
What are the main stages the LCA looks at
Extraction (of materials)
Manufacture
Distribution
Use
Disposal
What information does the LCA collect
Information on
Sustainability
Environmental impact
Lifespan
Disposal
How can data collected in the LCA be used to improve a product
You can look at energy use in one section and compare it to others in order to see what you should improve
What is one factor you dont look at in the LCA
Cost
What is a landfill
Waste disposal where waste is put in the ground
What is recycling
Processing a used material or object so that its substance can be used
What do you need to consider when disposing raw materials
Conserving limited raw materials
Reducing waste
Reducing the release of harmful chemicals
How do you decide if a material should be recycled
How easy the waste can be collected / sorted
The amount of any by-products released by recycling
The cost of recycling
How is paper recycled
Paper is mixed with water, cleaned then rolled and heated to make new paper
How are metals recycled
By heating
The molten metal is poured into moulds to produce new blocks called ingots
How is glass recycled
It is heated and moulded into new objects
How are polymers recycled
Polymers like polyethylene are heated and melted to form new objects
What is the symbol equation for the harbour process and how is ammonia converted from a liquid to a gas
N2 + 3H2 → 2NH3
The ammonia is cooled by tubes of cooling water
What are the benefits of using a higher atom economy
Reduces production of unwanted products
Process is more sustainable
Waste products produced might not be harmfull
How can bioleaching be harmful to the environment
Sulfuric acid could escape into the soil or any water supplies
What happens to the yield if the equilibrium shift to the left
Yield of backwards reaction increases
Yield of forward reaction decreases
