Mole Concept & Stoichiometry Flashcards
Relative atomic mass
The relative atomic mass, Ar, of an element is denied as the ratio of the average mass of one atom of the element to 1/12 of the mass of an atom of 12C isotope.
Relative isotopic mass
The relative isotopic mass, Ar, of a particular isotope is defined as the ratio of the mass of one atom of the isotope to 1/12 of the mass of an atom of 12C isotope.
Relative molecular mass
The relative molecular mass, Mr, of a substance is defined as the ratio of the average mass of one molecule to 1/12 of the mass of an atom of 12C isotope.
Isotopes
Atoms of the same element that have the same number of protons but different number of neutrons
Relative isotopic abundance (of each isotope in a sample)
Proportion of each isotope in a sample
Relative abundance = Percentage of the isotope of the sample by mass
Mole
The amount of substance contain a number of particles equal to the Avogadro’s constant (6.02 x 1023 mol-1)
Avogadro’s constant L
- 6.02 x 1023 mol-1
- Therefore number of particles = mol x L
Molar mass M
- The mass of one mole of a substance
- Units: g mol-1
- Therefore mass of substance = mol x M
Molar gas volume Vm
- The volume that one mole of gas occupies at a particular set of
temperature and pressure - At stp 273 K and 105 Pa/1 bar
1 mol of any gas occupies 22.7 dm3 - At rtp 293 K and 101325 Pa/1 atm
1 mol of any gas occupies 24.0 dm3 - Therefore volume of gas = mol x Vm
Concentration
- Amount of solute (mol or g), dissolved per unit volume of solution
- concentration = (mass or mol) / volume
- can also expressed as parts per million or parts per billion
Empirical formula
The simplest ratio of the atoms of the different elements in a compound
Molecular formula
The actual ratio of the atoms of the different elements in a compound
Limiting reagents
- Reactant that is not in excess
- Reactant that is completely used up in the reaction
Complete combustion of hydrocarbons
CxHy + (x + y/4) O2 → xCO2 +y/2H2O
Avogadro’s Hypothesis
Two equal volumes of gases , under the same T and P, contain the same number of molecules
Percentage Purity
(mass of pure sample/mass of total impure sample) x 100%
Percentage yield
(actual yield/theoretical yield) x 100%
Acid-base reaction
acid + base = salt + water
nacid/nbase = [acid]/[base]
Dilution
- Addition of more solvent to a given solution
- The amount of solute present does not change
-
Concentration decreases; the solute is now dispersed in larger final
volume - Amount of solute before dilution = Amount of solute after dilution
- C1V1 = C1V2
Double indicator titration
- When a weak diprotic acid, carbonate, etc is neutralised, it
undergoes 2 stages of reaction - Hence when titrating such reagents, each stage of neutralization can be detected by using different indicators
Sampling
- Collection of a portion from a given solution
- The concentration of sample is the same as the original solution
- The amount of solute present changes
- Concentration of original solution = Concentration of sampled
solution - n1/V1 = n1/V1
- Scaling factor = V2/V1
Continuous double indicator titration
- Uses two indicators in the same solution to detect the end point of a
titration process - Involves performing two titrations of the same analyte back-to-back,
with the first titration using one indicator and the second using
another - The titration is considered continuous because the second indicator
is added after the first titration is complete
Discontinuous double indicator titration
- Uses two separate solutions with a different indicator each
- Conduct two separate titrations for each stage of neutralisation
- The titration is considered discontinuous because the two stages of
neutralisation occur in two separate titrations
