Unit 1: Section 2: Amount of substance Flashcards
What is a mole
6.02 x 10^23 particles
How would you work out how many particles are in 0.450 moles of iron
0.450 x 6.02 x 10^23
How do you work out the mass of 1 mole of a element or compound
It’s the same as the Mr
What is the equation that links mass, moles and Mr
Number of moles = mass/Mr
What is the concentration of a solution and what is the unit
How many moles are dissolved per 1 dm ^3 of solution
The units are mol dm^-3
What is the equation that links number of moles and concentration
Number of moles = Concentration x Volume (cm^3) / 1000
OR
Number of moles = Concentration x Volume (dm^3)
What is the purpose of the ideal gas equation
Lets you find the number of moles in a certain volume at any temp or pressure
What is the ideal gas equation
Pressure (Pa) x Volume (m^3) = Number of Moles x Gas Constant (8.31 J K^-1) x Temp (Kelvin)
How do you convert from Celsius to Kelvin
Add 273
How do you derive an ionic equation from an equation
Make sure it is balanced
Split up into ions
Cross out the ions that are in both reactants and products
Find the mass of Iron (III) oxide produced when 28g of Iron is burnt in air
2Fe(s) + 1.5O2 -> Fe203(s)
Work out how many moles of iron - 28/55.8 = 0.502 moles of iron
Molar ratio of Fe : Fe2O3 is 2:1 so 0.502/2 = 0.251
Mr of Fe2O3 = 159.6
159.6 x 0.251 = 40 g
What do you have to do before a titration
Make a standard solution
What does aqueous mean
Solution in water
What is neutralisation
When an acid reacts with an alkali you get a salt and water
What is a standard solution
Any solution that you know the exact concentration of
How do you make a standard solution
Dissolve a known amount of solid in a known amount of water to create a known concentration
What is another word for standard solution
Volumetric solutions
How would you make a standard solution for sodium hydroxide
Work out the moles using concentration x volume
Work out mass using mass/Mr
Place weighing bottle on digital balance - weight required mass of solid and tip into beaker
Weigh weighing bottle and subtract the mass of bottle from mass of solid
Add distilled water to beaker and stir until sodium hydroxide has dissolved
Tip solution into volumetric flask and use a funnel to make sure all of it go on
Rinse beaker, stirring rod and funnel with distilled water
Top flask up to correct volume with distilled water (make sure bottom of meniscus reaches the line)
Mix contents of flask
Then calculate the concentration of the solution
How do you perform titrations
Use pipette to measure set volume of the solution that you want to know the concentration of
Put in a flask
Add a few drops of an appropriate indicator to the flask
Fill beaker with standard solution of the acid
Use funnel and pour acid into burette (do below eye level to avoid splashing)
Do rough titration to find out the end point
Then do accurate titration - take initial reading, then run the acid in to within 2cm^3 of the end point
Find amount of acid needed to neutralise the alkali = initial reading - final reading (this is called a titre)
Repeat a few times until you have three results within 0.1cm^3 of each other (concordant)
Use results from each to find the mean volume of acid used
Leave out any anomalous results
What type of indicators are used in titrations
Ones that change colour quickly over a very small pH range so you know exactly when the reaction has ended
What are the two indicators used in titrations
Methyl orange
Phenolphthalein
What are the colours of methyl orange in alkalis and acids
Alkali - Yellow
Acid - Red
What are the phenolphthalein in alkalis and acids
Alkali - Pink
Acids - Colourless
What is the equation for volume
moles x 24 dm^3
Give the difference of the empirical and the molecular formula
Empirical gives ratio of atoms in compound and molecular gives the exact amount of atoms in the compound
A molecule has an empirical formula of C4H3O2, and a relative molecular mass of 166. Work out its molecular formula
(4x12) + (3x1) + (2x16) = 83
166/83 = 2
2 x C4H3H02 = C8H6O4
C8H6O4 is the molecular formula
Compound is found to have percentage composition 56.5% potassium, 8.7% carbon and 34.8% oxygen by mass. Calculate its empirical formula
Assume its 100g of the compound
56.5 g = Potassium
8.7g = Carbon
34.8g = Oxygen
56.5/39.1 = 1.45 moles
8.7/12 = 0.725 moles
34.8/16 = 2.18 moles
1.45/0.725 = 2
0.725/0.725 = 1
2.18/0.725 = 4
K2CO3
What is the theoretical yield
The mass of a product that should be formed in a chemical reaction
What is the formula for percentage yield
(Actual Yield / Theoretical Yield) x 100
What is atom economy
The proportion of reactant atoms that become a part of the desired product in the balanced chemical equation
What are the economic advantages to a high atom economy
More efficient use of a company’s raw materials
Low atom economies will require more of raw materials to produce the same amount and this will cost money
There will be less waste to deal with
What are the environmental and ethical advantages to a high atom economy
Many raw materials are in limited supply so they should be used as efficiently as possible
Producing less waste is better for the environment
More sustainable
If the process is more efficient it will be cheaper which can also lead to low prices for medicines so it is more accessible
What is the formula for percentage atom economy
% Atom Economy = (Molecular Mass of Desired Product / Sum of Molecular Masses of all Reactants) x 100
