Moles Flashcards
Mole
The amount of any substance containing as many particles as there are in exactly 12g of the carbon - 12 isotope.
the number of particles in one mole is 6.02 x 10^23
number of particles = amount of substance (mol) x Avogadro constant
Avogadro constant (NA)
The number of atoms per mole of the carbon - 12 isotope.
6.02 x 10^23
Molar mass(M)
The mass of one mole
unit ~ g mol^-1
Moles in a solid equation
number of moles (n) (mol) =
mass (m)(g) /molar mass (M) (g mol^-1)
Avogadro constant calculations
number of particles = moles x avogadro constant
number of atoms = final answer x number of atoms. ( e.g NH3 has 3 atoms)
number of electrons = final answer x proton number
Molecular formula
Tells us the element in a molecule and the number of atoms of each element.
A molecule consists of two or more atoms bonded together by covalent bonds.
empirical formula
Tells us the simplest whole number ratio of the atoms of each element in a compound.
Calculating empirical formulae
- write down the elements and their masses underneath.
2.caculate the moles of each element by dividing the mass by the mass number.
3.divide each number by the smallest number of moles to find the simple ratio of the elements.
- state the empirical formula ,EF
Molecular formula calculation
MF= Molar mass / RFM of EF x EF
Molar gas equation
moles of gas = volume ( dm^3) / 24 dm^3
1dm^3 = 1000cm^3
what is the volume of one mole of a gas
1 mole of any gas , occupies a volume of 24000cm cubed or 24dm cubed at RTP ( room temperature and pressure)
1 mole = 24 dm^3
room temperature = 20 degrees
room pressure = 101kPa / 1atm
The ideal gas equation
pV=nRT
p= pressure (Pa)
V= volume (m^3)
n = amount of gas molecules (mol)
R = ideal gas constant (8.314 J mol-1 K-1)
T = temperature (kelvin K)
The assumptions made about the molecules in an ideal gas are :
- they are random in motion
- their collisions are elastic ~ no loss in kinetic energy)
- they are perfect spheres and negligible (small) in size.
- do not experience any intermolecular forces
- they exert pressure when they collide with each other and the walls of the container.
- their kinetic energy increase with temperature.
conversions for the ideal gas equation
Volume :
1m^3 = 1000000 cm^3
1m^3 = 1000 dm^3
Pressure:
1KPa = 1000Pa
1atm = 101325 Pa
Temperature:
degrees Celsius to kelvin ~ add 273
Calculating moles in solutions:
Moles (mol) =
volume (dm^3) x concentration (mol/dm^3 OR mol dm^-3)
1 dm^3 = 1000 cm^3
Solutions
- formed when a solute is dissolved in a solvent.
- The concentration depends upon how much of a solute is dissolved in a volume of solvent.
- Dilute solution ~ contains a LOW number of solute per unit volume of the solvent (low concentration)
- Concentrated solution ~ contains a HIGH number of solute per unit volume of the solvent. (high concentration)
Concentration
The amount of solute ,in mol , dissolved per 1dm^3
- A 1 molar solution is where one mole of a substance is dissolved in 1000cm^3 of water.
(1M = 1 mol dm^-3) - concentration can also be expressed in grams per dm^3 (g dm ^-3)
Conversion of (mol dm ^-3) to (g dm^-3)
multiply the concentration value by the molar mass.
(mass = moles x molar mass)
Stoichiometry & the three - step approach
- Refers to the MOLAR RELATONSHIP between the reactants and the products in a reaction.
- Calculate the MOLES of the substance using the information in the question.
2.Using the MOLAR RATIO , deduce the moles of the substance being ASKED FOR.
3.Calculate the QUANTITY being asked for using the moles of the substance.
