Amount of Substance Flashcards
Relative Atomic Mass
Weighted average mass of an atom compared to 1/12th mass of a C-12 atom
Relative molecular mass
Weighted average mass of a molecule compared to 1/12th mass of a C-12 atom
Avogadro’s number
6 x 10^23 - number of entities in a mole
Mole calculation for pure solids and gases
n = m/ Mr
Mole calculation for gases
PV = nRT
Units for gas mole equation
P = Pa V = m^3 T = K
Mole equation for solutions
n = cv
Units for solution mole equation
V = dm^3 C = mol dm^-3
Converting oC –> K
+ 273
Converting cm^3 –> dm^3
/ 1000
converting cm^3 –> m^3
/ 100 000
converting dm^3 –> m^3
/ 1000
Density equation
D (g cm^-3) = mass / volume
Empirical Formula
Simplest whole number ratio of atoms of each element in a compound
Method for empirical formula
Divide each mass of element by its Ar.
Divide through by the smallest number.
Find a whole number ratio without rounding
Molecular Formula
Actual number of atoms of each element in a compound
How to find Mr on a mass spectrometer
The furthest peak to the right is the molecular ion peak M+
Turn concentration in g dm^-3 to mol dm^-3
g dm^-3 = mol dm^-3 x Mr
% yield
= actual yield / theoretical yield x 100
% atom economy
mass of useful products / mass of all reactants x 100
Rule of 1 mole of gas at RTP
Will have a volume of 24 dm^3. n = V/24
Method to make a standard solution
- Weigh out required mass in weighing bottle.
- Tip contents into a beaker and add enough water to dissolve.
- Pour solution into a volumetric flask with a funnel.
- Wash beaker, funnel and stirring rod with water.
- Make solution up to the mark on flask.
- Invert flask several times to mix solution.
- Reweigh weighing bottle to calculate exact mass in flask.
Titration method
- Rinse burette and pipette with solutions to go into them.
- Pipette one solution into conical flask.
- Fill burette making sure jet space is filled.
- Add a couple of drops of indicator to conical flask.
- Mix solutions together swirling constantly and adding dropwise near end point.
- Repeat titration until 2 concordant results within 0.1 of each other.
- Record all titre values to 2 dp
Calculating % error
apparatus error/ measurement made x 100
Total % error
Add all equipment errors together
How to decrease apparatus error
Use equipment with a greater resolution (more dp or graduands). Increase the size of measurements i.e. scale up expt.
% difference between actual value and calculated value
(actual value - calculated value) / actual value x 100
