3.1.2 Amount of Substance Flashcards
How many particles in a mole (mol)?
6.02x10(23) (Avogadro’s Constant)
What is the equation for Number of particles?
No. of particles = (No. of moles x Avogadro’s Constant)
What is the equation to work out the mass of a substance?
Mass = Mr Mol
What is the equation to work out the concentration of a solution?
Conc = mol/vol
What is the Ideal Gas Equation?
pV = nRT
pressure (Pa) x volume (m3) = no. of mols x 8.31 x Temp (K)
How many Pascals (Pa) in a kilopascal (kPa)?
1 kPa = 1000 Pa
What do Ionic Equations shows?
Only show the Reacting Particles e.g. HNO3 + NaOH ⟶ NaNO3 + H2O would be: H+ + NO3- + Na+ + OH- ⟶ Na+ + NO3- + H2O H+ + OH- ⟶ H2O
What are the different state symbols?
(s) – solid
(l) – liquid
(g) – gas
(aq) – aqueous
What is the equation for number of moles in a solution?
No. of moles, n = (conc, c (mol/dm3) x vol, V (cm3))/1000
What is Boyle’s Law?
Product of Pressure and Volume is a constant as long as temperature remains constant
What is Boyle’s Law Equation?
Pressure P x Volume V = constant
What is Charles’ Law?
Volume is proportional to the temperature as long as the pressure remains constant
What is Charles’s Law Equation?
Volume V is Directly Proportional to Temperature T
AND
Volume V ÷ Temperature T = Constant
What is Gay-Lussac’s Law (a.k.a. Constant Volume Law)?
Pressure is proportional to the temperature as long as the volume is constant
What is Gay-Lussac’s equation?
Pressure P is Directly Proportional to Temperature T
AND
Pressure P ÷ Temperature T = Constant
What is the equation if you combine Gay-Lussac’s, Charles’ and Boyle’s Laws equations?
(Pressure P x Volume V) ÷ Temperature T = Constant for a fixed mass of gas
How do you make a Standard Solution?
e.g. Make 250cm3 of a 2M solution of NaOH
1) Work out # of moles of NaOH you need using Mol = Conc x Vol – 2 x 0.250 = 0.5 mol
2) Work out mass required using Mass = Mr Mol – 0.500 x 40 = 20.0g of NaOH
3) Place a weighing boat on digital balances and zero the balance, then weigh out 20g of solid. Tip into beaker.
4) Add Distilled (or De-ionised) Water and stir until all NaOH has dissolved
5) Tip solution into Volumetric Flask – make sure it is right size (250cm3 in this case). Use a funnel
6) Rinse the beaker and stirring rod with distilled water and add that to the flask too.
7) Top up flask to correct volume. Make sure bottom of Meniscus reaches the line. When close to the line, add drop by drop – if you go over start again
8) Stopper the flask and turn it upside down/mix a few times
How do you do a Titration?
1) Do a rough Titration to get an idea of where the end point is. Add the acid to the alkali using a burette, swirling flask regularly
2) Now do accurate Titration. Take initial reading to see exactly how much acid is in burette. Then run acid in to within 2cm3 of end point. When you reach this point, add dropwise
3) Work out amount of acid used to neutralise the alkali (Titre). This is final reading minus initial reading.
4) Repeat titration a few times, until you have at least 3 concordant results
5) Use results to work out mean Titre - leave out any anomalies
What are the two main indicators for Titrations?
1) Methyl Orange - Red in acid, yellow in alkali
2) Phenolphthalein - Colourless in acid, pink in alkali
Why should you do Titration of white tile?
Makes it easier to see exactly where end point is
What is the Empirical Formula?
Empirical Formula gives simplest whole number ratio of atoms of each element in a compound
What is the Molecular Formula?
Gives the Actual Numbers of atoms of each element in a compound
e.g. Glucose = C6H12O6
What is Molecular Formula made up of?
Whole number of Empirical Units
What are the 3 main steps to work out the Empirical Formula?
1) Find masses of each of the elements present in a compound (by experiment)
2) Work out the number of moles of atoms of each element
No. of moles = Mass of Element ÷ Mass of 1 mol of element
3) Convert the number of moles of each element into a whole number ratio
What is the Theoretical Yield?
Mass of the product that should be formed in a chemical reaction. It assumes no chemicals are ‘lost’ in the process
What is the equation for Percentage Yield?
Percentage Yield = (Actual Yield ÷ Theoretical Yield) x 100
How do you work out the Theoretical Yield of Aspirin?
Mass of Salicylic (2-hydroxybenzenecarboxylic) acid = 6g
Mol of Salicylic = 6 ÷ 138 = 0.0435 mol (to 3sf)
Mr of Aspirin = 180
Mass of Aspirin = 180 x 0.0435 = 7.83g (to 3sf)
Example Question
What is the Percentage Yield of Aspirin (2-ethanoylhydroxybenzenecarboxylic acid / Acetylsalicylic Acid) when Theoretical yield = 7.83g and actual yield of Aspirin is 5.95g
- 95 ÷ 7.83 = 0.7598978289
0. 7598978289 x 100 = 76.0% (to 3sf)
What is the equation for Atom Economy?
% Atom Econ = (Mr of Desired Prod ÷ Sum of Mr of all reactants) x 100
What is the Atom Economy for Acetylsalicylic Acid (Aspirin) when formed using 2-hydroxybenzenecarboxylic acid (Salicylic Acid) and Ethanoic (or Acetic) Anhydride?
180 ÷ (138 + 102) = 0.75
0.75 x 100 = 75%
