Amount of Substance Flashcards
What is the definition of the relative atomic mass?
The relative atomic mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon - 12.
What is the Avogadro’s number / constant?
One mole of a substance is equal to 6.022 times 10^23 units of that substance.
What is the equation for moles?
moles ( mol) = mass ( grams) / Mr ( must be calculated to 1dp)
What is the equation for gases?
PV = nRT
unit for pressure ( P ) = Pa
unit for volume ( V ) = m^3
unit of temperature ( T ) = K
n = moles
R = 8.31
°C—> K add 273
cm^3 to dm^3 = divide by 1000
dm^3 to m^3 = divide by 1000
What is the equation for solutions?
concentration = moles/ volume
concentration = mol dm^-3
volume = dm^ 3
Find the mass of 200cm^3 of carbon monoxide, CO, and carbon monoxide, at 17°C and a pressure of 98900Pa.
200/ (1000 × 1000 ) = 2 × 10 ^ -4 m ^3
17°C = 290 K
PV = nRT
n = PV / RT
n = 98900 × 2 × 10^-4 / 8.31 × 290
n = 8.21 moles
Mr of CO = 28
Moles × Mr = Mass
8.31 × 28 = 229. 88 mg
What does it mean by the empirical formulae?
An empirical formula is the simplest ratio of atoms of each element in the compound.
What does it mean by molecular formula?
A molecular formula is the number of atoms in each element in that compound.
How do you work out empirical formulae?
- Divide each mass by the atomic mass of the element to give moles.
- For each of the answers from step 1 divide by the smallest one of those numbers.
Why can the heating in a crucible method be used?
This method can be used for measuring mass loss in thermal decomposition reactions and also for mass gain when reacting magnesium in oxygen.
What is the equation for mass concentration?
Mass concetration= mass/volume
mass concentration = g dm ^-3
unit of mass = g
unit of volume = dm^3
