Chapter 2 - Amount of Substance Flashcards
define relative atomic mass
the average mass of an atom relative to one twelfth of the average mass of a carbon 12 atom
average mass of one atom of an element*12/mass of one carbon-12 atom
what is relative molecular mass
the same as relative atomic mass but the average mass of one molecule
you can find this mass by adding up all the relative masses in a molecule
what is relative formula mass
a way to measure the mass of one repeating unit in an ionic compound because they dont exist as molecules but rather a giant lattice
what is the avogadro constant
6.022 x 10^23
what is the significance of the avogadro constant
the number of atoms or molecules in one mole of a substance
one mole of a substance is equal to the Mr or Ar in grams
The Avogadro constant or Avogadro number is the number of atoms in 12 g of carbon-12.
how can you find the mass of one atom of a substance in Kg
(mass/1000)/6.022*10^23
what is a solute
the substance that is dissolved in a solvent
what is a solvent
the substance that dissolves the solute
what is a solution
a combination of a dissolved solute and a solvent
what does concentration indicate
the amount of a substance in one dm^3 of said substance
what is boyles law
as long as the temperature is constant, the product of the pressure and the volume is constant
what is charles’ law
The volume is proportional to the temperature as long as the pressure
remains constant
pressure/temperature = constant
what is the constant volume law
The pressure is proportional to the temperature as long as the volume
remains constant.
pressure/temperature = constant
what is the ideal gas equation
pV=nRT
what is back titration
a substance of an unknown concentration is titrated with a substance of a known concentration in excess.
the resulting mixture is titrated with another substance of known conc.
the moles reacted can be subtracted from the total moles used to find how many moles reacted in the initial reaction.
this can then be used to find the concentration of the unknown substance.
when are back titratoins used
when the reaction is slow, the substance is not pure, the reaction is difficult to observe, the analyte is a non-soluble solid
when do we use relative formula mass
when we have a giant covalent or ionic lattice
define a mole
6.022 x 10^23 units of a substance
define concentration
the amount of a solute (in g or mol) per unit volume (always dm^3)
what assumptions are made for the motion of gas particles
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.
what is an ideal gas
a gas which obeys all the assumptions made in kinetic theory and can be exactrly represented using the ideal gas equation at room temp and pressure
what is the difference between the empirical and molecular formula
empirical formula gives the lowest whole number ratio of elements present in a compound while the molecular formula shows the actual number of atoms of each element present in a compound
how can you calculate empirical formula from percentage composition by mass
assume the total sample size is 100g
find the moles of each element present by dividing the percentage by the Ar
find the lowest whole number ratio of the moles
how can you find the molecular formula from the empirical formula
calculate the empirical formula mass
then divide the molecular formula mass by the empirical formula mass
multiply the ratio of atoms in the empirical formula by the resulting number
