Chemistry Calculations Flashcards
Molecular Mass (Mr)
The Molecular Mass (Mr) is the ‘ sum of the atomic masses of all atoms in a molecule.’ We are only talking about the mass of ONE molecule.
Molar Mass
The Molar Mass is ‘ the sum of the atomic masses of all atoms in a molecule, in 6.02 x 10^23 formula units of the substance (1 mole).’
The Mole
The mole contains 6.02 x 10^23 formula units.
n=m/Mr
moles to ‘n’, mass to ‘m’, molecular mass to ‘Mr’
N=nxNa
n=moles, N=number of particles, Na=Avogrado’s number
%composition = (mass of elements/mass of compound) x 100
%composition = (mass of elements/mass of compound) x 100
Water of crystallization
When ionic salts form, cations are attracted to anions (and vice versa). They form giant ionic lattices.
Sometimes, water molecules can get trapped within the lattice which contributes to the Mr of the ionic compund. We call them ‘hydrated’. The formulae of these compounds look slightly differently. For example; CuSO4 . 2H2O2
This formula tells us that for every 1 mole of copper sulfate, 2 moles of water gets trapped in the lattice.
We can heat the compound to get rid of the water. It is then classed as ‘anhydrous’.
Empirical formula
The empirical formula for a compound can be defined as ‘the simplest whole number ratio of elements in a compound.’
Molecular formula
The molecular formula (MF) will always be a multiple of your empirical formula (EF).
EF multiplier = (mass of compound/mass of EF)
n=cV
c=mol/L, V=Litres, n=moles
Concentration is defined as “the amount of solute in a given volume of solution.”
Concentration
Max amount of solute in a solvent =
saturated
What is titration?
Titration is a technique to find the concentration of a solution. One of the solutions must have an accurately known concentration. A titration allows us to find the volume of the known concentration and thus, calculate the concentration of an unknown.
Step 1 of titration
Using a pipette, add set volume of unknown solution to a conical flask
Step 2 of titration
Add 2-3 drops of indicator
Step 3 of titration
Fill burette with solution of known concentration. Ensure it is levelled off to exactly 0mL
step 4 OF TITRATION
Slowly add solution from the burette (known) to the solution in the conical flask (unknown)
Step 5 of titration
Swirl flask to continuously mix
Step 6 of titration
Stop adding known solution from burette as soon as the reaction is complete (often recognized by the appropriate colour change)
Record final volume of the burette
Step 7
Step 8 of titration
Repeat until you have concordant results (within 0.1mL)
In titration, where does the solution with known concentration go?
Burette
In titration, how do we transfer a volume of the unknown solution?
Pipette
In titration, what allows us to see the colour change?
A white tile
