Unit 14, 15 & 16 - Quanititative analysis/ Dynamic Equilibra, Calculations Involving Volumes Of Gases/ Chemical Cells And Fuel Cells Flashcards
(54 cards)
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
