do you understand avagadros number and the formulas that are used?
i.e.
n = moles
MW = molecular weght (sometimes referred to as molecular mass)
m = mass (grams)
N = number of atoms
Na = Avagadros number - 6.022 x 10^23
Formulas
n = m/MW
Example
How many moles are contained in each substance given below?
(a) 1.01 g of neon gas (Ne)
(b) 2.538 g of iodine molecules (I2)
(a) n = 1.01 g/20.18g/mol = 0.05 moles
(b) n = 2.538 g/253.80 g/mol = 0.01
n = N/Na
Example
For 3.011 x 10^23 atoms of C-12. How many moles do we have?
n = ?
N = 3.011 x 10^23
Na = 6.022 x 10^23
n = 3.011 x 10^23/6.022 x 10^23
n= 0.5 moles
Molar Volume of Gases
STP - Standard Temperature and Pressure
Temperature 0*
Pressure 101.3KPa
Vm 22.41 L/mol
SLP - standard Laboratory Condition
Temperature 25*
Pressure 101.3KPa
Vm 24.47L/mol
n = moles
V = Volume
Vm = Molar Volume
n = V / Vm
Example
Calculate the
(a) Number of moles
(b) mass of methane (CH4) in 5.0L of the gas at STP (Standard Temperature and Pressure)
(a)
n = V / Vm
n = 5.0L / 22.41L/mol
n = 0.22 moles
(b)
n = m / M
0.22 = m / 16.05g/mol
m = 3.53 g
Hope this helps you. Good luck~!