Amount of substances Flashcards
what is relative atomic mass
Therelative atomic mass(Ar) of an element is the weighted average mass of all its naturally occurring isotopes
what is relative formula mass
The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of all the atoms in the compound’s formula unit
how do u calculate the relative atomic mass ar
Multiply each isotope’s relative isotopic mass by its isotopic abundance.
Sum these quantities.
Divide by the sum of the isotopic abundances.
what does the y and x axis show in the mass spectrum
the y axis shows the percentage abundance and the x axis shows the mass/charge
how do you calculate the relative formula mass
Step 1: Write down the molecular formula
H2O
Step 2: Multipy each element’s atom count by its Ar
H: 1.0 × 2 = 2.0
O: 16.0 × 1 = 16.0
Step 3: Calculate Mr
Relative molecular mass = 2.0 + 16.0 = 18.0
what is a mole
Themoleis a convenient unit that allows us to count extremely large numbers of atoms and molecules.
what is the avogadros connstant ( and the number )
Avogadro’s constanthas a value of6.02 x 1023. This very large number represents how many particles are contained in one mole.
what is the triangle that links avogadros constant no.of particles and number of moles
no.of moles = no.of particles / avogadro cons.
what is the molar mass
Themolar mass(M) represents the mass in grams of 1 mole of a given substance.
what is the triangle that links mass in g molar mass and no. of moles
no.moles=mass in g / molar mass
what is the unit for molar mass
g/mol^-1
what is the concentration of a solution measured in
g/dm^-3 or mol/dm^-3
what is the equation linking mass,volume and concentration
concentration= mass/ volume
what is the equation linking moles,volume and concentration
concentration= moles/ volume
how do you convert cm3 to dm3
divide by 1000
how do convert dm3 to cm3
multiply by 1000
how do you convert g/dm^-3 to mol/dm^-3
Divide the concentration in g dm-3by the Mrof the solute
For example, a 58.5 g dm-3solution of NaCl (Mr= 58.5)= 1.00 mol dm-3
how do u convert mol dm-3to g dm-3
Multiply the concentration in mol dm-3by the Mrof the solute
For example, a 2.00 mol dm-3solution of NaCl (Mr= 58.5)= 117 g dm-3
what are the assumptions that the ideal gas equation obeys
Gas particles move rapidly and randomly.
The volume of the actual gas particles is negligible compared to empty space between them.
There are no intermolecular attractions or repulsions.
Collisions between particles are elastic - no energy is lost.
The average kinetic energy of particles depends only on their temperature.
why does the real gas deviate from these assumptions
because they have weak intermolecular attractions and non negligible volumes
what are the names of the two gases that come close to the ideal gas
noble gases like helium and neon because their intermolecular forces are minimal
what is the formula for ideal gas
pressure (pa) X volume(m3) = moles of gas X the gas constant X temperature (K)
what is teh value for the gas constant
8.31
how do u convert kPa to Pa
multiply by 1000
how do u convert degree celcius to kelcius
add 273 to the original number
how do u convert cm3 to m3
divide 1,000,000
what is the empirical formula
The empirical formula gives the simplest whole number ratio of atoms of each element present in a compound.
what is the molecular formula
The molecular formula gives the actual number and type of atoms of each element in a molecule.
give an example of both empiral and molecular formular
An empirical formula of CH2O as this gives the simplest ratio.
A molecular formula of C6H12O6as this shows the actual numbers of atoms in a glucose molecule.
what are the two ways to find the empirical formula
percentage composition
combustion data
explain how to find the empiraical forrmula from the percentage composition
- assume that all the percentages are in g
- then find the number of moles in each molecule
- find the ratio btw them by dividing everything by the smallest no of moles
explain the way from a combustion data
A hydrocarbon sample weighing 2.20 g was completely combusted in oxygen, producing 3.30 g of CO2and 1.35 g of H2O.
Determine the empirical formula of the hydrocarbon.
Step 1: Calculate moles of CO2produced
moles of CO2 =Mr mass=44.03.30=0.075 mol
Step 2: Calculate moles of carbon in the sample
Each molecule of CO2contains 1 atom of carbon.
Moles of C atoms = Moles of CO2= 0.075 mol
Step 3: Calculate moles of H2O produced
moles of H2O =Mr mass=18.01.35=0.075 mol
Step 4: Calculate moles of hydrogen in the sample
Each molecule of H2Ocontains 2 atoms of hydrogen.
Moles of H atoms = 2 x moles of H2O= 2 x 0.075 = 0.150 mol
Step 5: Determine the simplest C : H mole ratio
C : H = 0.075 : 0.150 = 1 : 2
Step 6: Write the empirical formula
The empirical formula is CH2.
what are the ways to calculate the molecular formulae
from the empiral formula
and from a hydrated ionic salt
how to u calculate the molecular mass fro the empiral formula
- finding the empiral formula form the question ( calculate the Mr )
- then divide the molecular mass by the empiral formula mass
- the number u get is the number present in the equation basically
how do u calculate the molecular formula from the hydrated ionic salt
calculate the mass of water lost
them moles of the anydrous thingy lost my dividing mass / Mr
then do the same for hydrated ( water)
then find the ratio
what is the formula to calculate the number of atoms
no.of atoms = amount of substance / moles X avogadro’s constant
