Amount of Substance Flashcards
Ionic equations
First disassociate all of the ions and cancel the ions that appear on both sides
Relative atomic mass
The average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
Relative molecular mass
Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of carbon-12.
What equation links mass, moles and Mr?
Moles = mass/Mr
What equation links moles, concentration and volume?
Moles = concentration x volume (dm³)
What is the ideal gas equation?
P(Pressure in pascals)V(volume in m³ ) = n(The number of moles)R(The gas constant 8.314)T(Temperature in kelvin)
How do you work out how many atoms you have of an element when you have the Mr and the mass?
Moles = mass/Mr
Moles x Avogadro constant (6.02 x 10²³)
Equation involving mass, density and volume?
Density = mass/volume
Empirical formula
An empirical formula is the simplest ratio of atoms of each element in a compound.
Molecular formula
A molecular formula is the actual number of atoms of each element in the compound.
What is percentage yield and how do you calculate it?
percentage yield = (actual yield/theoretical yield) x 100
What is percentage atom economy?
(Mr of useful products/total Mr of reactants) x 100
Why are all Mr values related to Carbon-12?
It is the agreed standard.
Give 3 reasons why the yield of an experiment might be lower than the expected value?
Other reactions are taking place
The reaction is reversible
The reactants were impure
Reactants/products still on apparatus
In a titration why is the volumetric flask containing your standard solution inverted multiple times?
To ensure that the concentration is equal throughout.
If you have already rinsed the burette and pipette with water why do you need to rinse them with solution?
The water could stick to the glassware and dilute the solution that is being added so by rinsing with the solution this will not change the concentration.
Why is it important to bleed the air out of the burette when doing a titration?
If any air remains in the burette it shows a false initial reading as no solution actually leaves the burette until later.
Why should you not force the solution out of the pipette with the filler if it is faster?
The filler leaves a small volume of solution at the bottom of the pipette which is accounted for which will occur due to capillary action from gravity. It could also damage the pipette.
Why should you not use lots of indicator in a titration?
Indicators in themselves are acidic (weak) and in order to get a colour change you really don’t need that much, so adding more than is needed just increase the volume of titrant needed to add to the solution.
Why is the conical flask held over a white tile?
The contrast between the white tile and the solution makes it easier to see an endpoint on the colour change.
How close do results need to be together to be concordant?
0.1cm³ of each other and you only need 2 to take a mean average
Given that the uncertainty of a titration came mainly from the burette how could you reduce the percentage uncertainty?
Use a more diluted acid
What are the potential errors when using a gas syringe?
Gas escapes before bung is inserted
Syringe sticks
How to decrease the percentage uncertainty when measuring masses?
Weigh before and after to find mass transferred
Why would a manufacturer want to produce something with less steps and a higher percentage atom economy?
Increases yield
decreases waste
