C3 Amount Of Substance Flashcards
What’s avogadros constant
6.02 x 10^23 mol^-1
The number of atoms per mole of the C-12 isotope
How to calculate the mass of 1 mole of the element
Mass of 1 mole = relative atomic mass in grams
State Avogadro’s law
Under same temp and press, 1 mole of any gas would occupy the same volume.
Define molar gas volume
Volume per mole of gas molecules at a stated temp & press
Why do diff gas particles occupy the same volume
Gas particles are very spread out, hence individual differences has no effect.
What are the ideal ways in which gases behave
They’re in continuous motion
No IMF’s experienced
Exert pressure when they collide with each other or container
No Ek is lost in collisions
When temp increases, Ek of gases also increase
1 atm is equal to how many Pa
1atm =1.0133 bars 101325 Pa
0*C is equal to how many kelvins
273K
What doe conc of a solution mean
Amount of solute dissolved in 1 dm^3 of solvent
What’s a standard solution
Solution of known conc
What does percentage yield mean
Efficiency of which reactants are converted into products
Reasons for not obtaining 100% yield
Reaction may be at equilibrium
Reactants may be impure
Side reactions could occur
Reactants/products may be left behind while transferring
Loss of products during separation & purification
What does atom economy tell us about
Proportion of desired products compared with all the products formed in the reaction
Is a measure of how well atoms have been utilised
Does 100% yield mean 100% atom economy
No
Even if all reactants are converted into products, not all products of reaction will be the required products
Which type of reaction has 100% atom economy
Addition reactions
(2 or more reactants are combined to form a product)
What’s the molecular formula
Number of atoms of each element in a molecule
What is empirical formula
Simplest whole number ratio of atoms of each element in a compound
What does hydrated and water of crystallisation mean
Water molecules are part of their crystalline structure
What does anhydrous mean
Doesn’t contain water molecules
What’s the method to find the formula of a hydrated salt
Weigh empty crucible
Add hydrated salt into weighed crucible
Weight crucible and hydrated salt
Using pipe clay triangle, support crucible containing hydrated salt on a tripod
Heat crucible & contents gently for about 1 min
Then heat it strongly for 3 more mins
Leave crucible to cool
Weight crucible and anhydrous salt
What are the assumptions made when finding the formula of a hydrated salt
All water has been lost - only see surface of crystals, there could be water inside - solution = heat to constant mass
No further decomposition - difficult to judge if there’s no colour change
what is molar gas volume at RTP
24.0 dm^3mol^-1
Formulas to calculate volume of gas in dm3 and cm3
n = V/24.0 dm3
n= V/24000 cm3
What are the assumptions for molecules making up an ideal gas
Random motion
Elastic collisions
Negligible size
No IMFs
Ideal gas equation
pV = nRT
Units are conversions for the ideal gas equation
p = Pa (pressure) kPa to Pa = x10^3
V = m^3 (volume) cm^3 to m^3 = x10^-6
dm^3 to m^3 = x10^-3
n = mol (amount of gas molecules)
R = 8.31 Jmol^-1K^-1 (ideal gas constant)
T = K (temperature) *C to Pa = +273
Method to find relative molecular mass
Add sample of volatile (l) to small syringe via needle
Weigh small syringe
Inject sample into gas syringe through self sealing rubber cap
Reweigh small syringe to find mass of volatile (l) added to gas syringe
Place gas syringe in boiling water bath at 100*C
(l) vaporises producing a gas
Pressure is recorded
Why is the theoretical yield hard to achieve
Reaction may not have gone to completion
Other reactions (side reactions) may have taken place alongside main reaction
Purification of product may result in loss of some product
Formula for percentage yield
(Actual/theoretical) x 100%
What is a limiting reagent
Reactant that’s not in excess
Used up first & stops reaction
In the 1:1 ratio It’s the reactant with higher moles
