Amounts of Substance Flashcards
(12 cards)
What is a mole?
The amount of substance that contains as many elementary particles as there are atoms in 12g of carbon 12
What is Avogadros constant?
The number of particles in each mole of carbon 12
6.02x10 23
How do we find number of particles?
Number of particles = moles (n) x avogadros constant
What is molar mass (Mr)?
The mass in grams in one mole of substance
Calculated by mass/n
How is moles calculated from volume with no concentration?
Divide by the molar gas volume
24 if dm3
24000 if cm3
What units should pV=nRT be in?
p = Pa
V = m3
T = K
n= mol
R = gas constant
How do you make a standard solution?
- weigh a known mass by difference using a mass balance
- dissolve in a small amount of deionised water in a beaker, mixing with a stirring rod, and transfer to a 250cm3 volumetric flask using a funnel
- rinse the beaker, funnel, and stirring rod with deionised water, pouring the rinsings into the volumetric flask
- carefully make up to the 250cm3 line with deionised water until the bottom of the meniscus reaches the 250cm3 marker line using a dropping pipette when near the end
- add a stopper to the flask and completely invert to mix
How is percentage uncertainty calculated?
Number of readings x uncertainty on equipment X100
———————————————————————
Quantity measured
BURETTES HAVE 2X READINGS
How to calculate percentage yield?
Actual yield
————————— X100
Theoretical yield
What is the limiting reagent?
If a reactant is not in excess, all moles of it will react, making it the limiting reagent
How to calculate the limiting reagent?
RICE method
R = reaction
I = initial moles
C = change
E = end moles
How to calculate atom economy?
Sum of Mr of desired product X100
——————————————
Sum of Mr of all products
