Amount of Substance Flashcards
Formula for Avagadro’s Constant
Number of particles= Number of Moles x Avagadro’s Constant
Formula for moles, mass, mr
Number of Moles= Mass of Substance -:- Mr
n=m -:- mr
Formula for calculating moles in solution
Number of Moles= Concentration (mol dm-3) x Volume (dm3)
n=cv
Ideal Gas Equation
Describe each part and give the units
pV=nRT
p= pressure (Pa) V= volume (m3) n= number of moles R= 8.31 J K-1 mol-1 T= temperature (K)
Changing temperature from oC to K
K= oC +273
1cm3 in m3
1 dm3 in m3
1 cm3 = 1 x 10-6 m3
1 dm3 = 1 x 10-3 m3
Standard Solution (aka volumetric solution)
Making a Standard Solution
Any solution that you know the exact concentration of.
Involves dissolving a known amount of solid in a known amount of water to create a known concentration
Empirical Formula
The simplest whole number ratio of all the atoms of each element in a compound
Molecular Formula
Made up of
The actual numbers of atoms of each element in a compound.
A whole number of empirical units
Percentage Yield
Actual Yield -:- Theoretical Yield x 100
Percentage Atom Economy
Molecular Mass of Desired Product -:- Sum of molecular masses of all reactants x 100
Spectator Ion
An ion that’s present in the reaction mixture, but doesn’t get involved in the reaction
Describe how to set up a titration (in full)
Use a pipette to measure out a set volume of the solution that you want to know the concentration of. Put it in a flask.
Add a few drops of an appropriate indicator to the flask.
Fill a burette with a standard solution of the acid.
Use a funnel to carefully pour the acid into the burette. Always do this below eye level to avoid any acid splashing onto your face or eyes (wear safety glasses)
Describe how to conduct an accurate titration
Firstly, do a rough titration to get an idea of where the end point is.
Add acid to the alkali using a burette, giving the flask a regular swirl.
Place the flask over a white tile to clearly see when the colour change occurs (ie when the end points is).
Do an accurate titration. Take an initial reading to see exactly how much acid is in the burette. Then run the acid in to within 2 cm3 of the end point.
When you get to this stage, add it dropwise. If you don’t notice exactly when the colour changes you’ll overshoot and your result won’t be accurate.
Work out the amount of acid used to neutralise the alkali. This is just the final reading minus the initial reading. This volume is known as the titre.
Repeat the titration a few times, until you have at least three results that are concordant (within 0.1 cm3 of each other).
Use the concordant results to calculate the mean (average) volume of acid used
End Point
The exact point where the alkali is neutralised and the indicator changes colour
