Unit 14, 15 & 16 - Quanititative analysis/ Dynamic Equilibra, Calculations Involving Volumes Of Gases/ Chemical Cells And Fuel Cells Flashcards
What is the theoretical yield?
The maximum mass of product that can be formed from a reactant.
What is the actual yield?
The amount of product obtained when you carry out an experiment.
What is the percentage yield?
It compares the actual yield and the theoretical yield
What does the theoretical yield assume?
That all the reactants are turned into products and the products are successfully separated from the reaction mixture.
Give 3 reasons why reactions do not give 100% yields
Incomplete reaction - not all reactants are used up
Some product is lost - some left behind in container
Unwanted side reactions - other products formed
Why is a higher yield better?
Fewer raw materials are used to make the same amount of product, more useful reaction.
What is atom economy?
A method of showing how efficient a particular reaction is at making use of the atoms in the reactants
Give an example of a reaction with 100% atom economy
Ethene + steam —> ethanol
Why does the production of ethanol by fermentation of sugars have a lower atom economy?
It produces carbon-dioxide as a by-product
Give a way to improve the atom economy of a reaction
To find uses fro the by-products
Give 2 reasons why chemists might choose to use fermentation for ethene production
Only 30-40 degrees needed
Uses renewable resources
Give 2 reasons why chemists would use a steam reaction to produce ethene
Fast
Creates pure ethene
What is a volumetric flask?
The apparatus used to make a solution with an accurate concentration
How do you make a solution using a volumetric flask
The solute is dissolved in distilled water, then made up to the graduation mark before stoppering and shaking the flask
What does it mean to measure from the bottom of the meniscus
To measure the reading from the lowest point of the ‘bowl’ shape of the solution
What is 1dm^3 the same as in cm
1000cm^3
What are acid-alkali titrations used to find
The exact volume of an acid that neutralises a specific volume of alkali or vice versa
What does the volume occupied by a sample of a gas depend on?
The temperature, pressure and number of particles of gas
What does Avogadro’s law state about gas volume
If the temperature and pressure are the same, equal volumes of different gases contain an equal number of molecules
What is the molar volume?
The volume occupied by one mole of molecules of any gas
What is the molar volume at room temperature and pressure (rtp)?
24 dm^3
How do plants absorb water and mineral ions?
Through their root hair cells
What happens if plants don’t get enough water or minerals
They can have defiance diseases such as stunted shoots and discoloured leaves
What is the role of fertilisers
To replace the mineral ions needed by the plants and to promote plant growth
What are the 3 elements found in artificial fertilisers?
Nitrogen, phosphorus, potassium
What are nitrogenous fertilisers
A source of soluble nitrogen compounds
Give 2 examples of a nitrogen-rich fertiliser
Ammonium nitrate, ammonium sulphate
What is the word equation for the production of ammonium nitrate
Ammonia + nitric acid —> ammonium nitrate
What is the symbol equation for the production of ammonium nitrate
NH3 + HNO3 —> NH4NO3
What process is ammonia manufactured by?
The Haber process
What is the word equation for the production of nitric acid from ammonia?
Ammonia + oxygen —> nitric acid + water
What is the word equation fo the production of ammonium sulphate?
Ammonia + sulphuric acid —> ammonium sulphate
Give 2 differences about preparing ammonium sulphate in the laboratory - industrial
Small scale - large scale
Batch - continuous
How is ammonium sulphate made industrially?
Through many stages
When does a reversible reaction reach an equilibrium
When they are in a closed system ( stoppered flask, nothing can escape)
What are 2 factors of dynamic equilibriums
The forward and backward reactions are at the same rate
The concentrations of all reacting substances do not change
Which direction does the position of the equilibrium move when something is altered?
To oppose any changes made
If the temperature is increased, which direction does the equilibrium move to?
Toward endothermic reaction (this takes in heat which opposes the added heat)
If the pressure is increased , which direction does the equilibrium move to?
Towards less molecules, to speed up this reaction to counteract the added molecules
If the concentration is increased , which direction does the equilibrium move to?
Towards lower concentration to even out the concentrations
Why might manufacturers not be able to use reactions that reach equilibrium?
It can take too long
What is the word equation for the Haber process?
Nitrogen + hydrogen —> ammonium
What is the symbol equation for the Haber process?
N2 + 3H2 —> 2NH3
How many atmospheres is the pressure chosen for the Haber process?
200 atmospheres
What is the temperature chosen for the Haber process?
450 degrees Celsius
Why does the Haber process not use high pressures or low temperatures?
Too expensive, too slow
Why is an iron catalyst used for the Haber process?
It’s doesn’t change the position of the equilibrium but it does speed up the reaction.
Why might a particular reaction pathway be chosen? (3 factors)
Availability and cost of raw materials and energy supplies
Rate of reaction and equilibrium position
Atom economy, yield, usefulness of by-products
If 2 metals are further away on the reactivity series in a circuit, what happens to the voltage
It is bigger
What does chemical cells contain (2) (Daniell cell)
2 different metals in a solution of one of their salts
A ‘salt bridge’ to allow dissolved ions to pass over
What type of reaction happens in Daniell cell
Exothermic, displacement
What is the product of a hydrogen-oxygen fuel cell
Water
How does a hydrogen-oxygen fuel cell work
Hydrogen on left side, oxygen on right side with electrodes with a membrane in between the electrodes.
H+ ion from H passes through membrane after attracted to electrode and 2 H+ bond to oxygen on other side
Why do hydrogen-oxygen fuel cells still on involve CO2
When H is manufactured, CO2 is a by product
