2.1 Atoms and reactions Flashcards
isotope definition
atoms of the same element but with different number of neutrons and mass number
atomic mass number
number of protons and neutrons in nucleus of an atom
atomic number
number of protons in nucleus
relative mass of electron
1/1836
relative isotopic mass definition
mass compared with 1/12th mass of carbon-12
relative atomic mass definition
weighted mean mass compared with 1/12th mass of carbon-12
relative formula mass used for
compounds with giant structures
relative molecular mass used for
simple molecules
mole (mol)
unit for amount of substance
Avogadro constant (NA)
number of particles per mole
6.02 x10^23 mol^-1
molar mass
mass per mole
g mol^-1
molar gas volume
gas volume per mole
units dm^3 mol^-1
empirical formula
simplest whole number ratio of atoms of each element in a compound
molecular formula
number and type of atoms of each element in a molecule
relationship between moles, mass and Ar
mass (g) = Ar x moles (mol)
relationship between concentration, volume and moles
moles (mol) = concentration (mol dm^-3) x volume (dm^3)
relationship between Ar, moles, ideal gas constant, pressure, temperature and volume
Moles (n) = pressure (Pa) x volume (dm^3) / ideal gas constant (8.3145 J K^-1 mol^-1) x temperature (K)
relationship between moles, molar gas volume and volume in RTP and normal pressures
moles = volume (dm^3) x 24 (dm^3)
anhydrous definition
without water
water of crystallisation definition
water bonded into a crystalline structure
degree of hydration definition
number of moles of water of crystallisation chemically bonded in 1 mole of the compound
hydrated definition
crystalline structure containing water molecule
standard / stock solution definition
solution of known concentration
stoichiometry definition
ratio of moles of each substance
why theoretical yield is not achieved
reaction not gone to completion
side reactions may have occurred
purification of production may result in loss of product
theoretical yield definition
maximum possible amount of product of a reaction
actual yield definition
actual amount of product of a reaction
percentage yield
conversion of starting materials into desired product
percentage yield formula
percentage yield (%) = actual yield / theoretical yield x 100%
limiting reagent definition
reactant completely used up first and stops reaction (e.g. not in excess)
atom economy definition
measure of how well atoms have been utilised
important of high atom economy reactions
large proportion of desires products to unwanted waste products
sustainable as make the best use of natural resources
atom economy formula
atom economy = (sum of molar masses of desired products / sum of molar masses of all products )x 100%
acid definition
proton donor
strong acid definition
acid that completely dissociates (releases all hydrogen atoms) in aqueous solution
weak acid definition
acid that partially disassociates (releases small proportion of hydrogen) in aqueous solution
base definition
substance that neutralises acid to form a salt
e.g. metal (hydr)oxides, metal carbonates and ammonia
alkali definition
base that releases hydroxide ions into solution
titration definition
technique used to accurately measure the volume of one solution that reacts exactly with another solution
titration uses
finding concentration of a solution
identification of unknown chemicals
finding purity of a substance
how to prepare standard solution
solid weighed accurately and dissolved in beaker using distilled water (less than will be needed to fill volumetric flask)
solution transferred to volumetric flask
rinse traces of solution using distilled water into flask
add distilled water until bottom of meniscus lines up with graduation line
invert flask multiple times to mix solution properly
careful of parallax error
acid-base titration procedure
add measured volume of one solution using pipette into conical flask
add other solution fo burette and record initial burette reading
add few drops on indicator to conical flask
slowly add solution in burette to conical flask while stirring until indicator changes colour
colour change = end point = volume of one solution that reacts exactly with other solution
titre calculated by subtracting final burette reading from initial burette reading
repeat until two accurate tires are concordant
end point definition
indicates volume of one solution exactly reacting with another
titre definition
volume of solution added from burette
subtract final burette reading from initial burette reading
concordant definition
agreeing to within 0.10 cm^3
reduction definition
gain of electrons
decrease in oxidation number
oxidation reaction
loss of electrons
decrease in oxidation number
redox reaction definition
reaction containing both reduction and oxidation
how to measure water of crystallisation
weigh empty crucible
add hydrated salt to crucible, weigh crucible again
heat using pipe-clay triangle to support crucible on tripod
heat for period of time
remove crucible, allow to cool (too hot affects mass reading) and reweigh
heat crucible for further period of time (until recorded constant mass)
problems in water of crystallisation practical
not all water lost -> heat until constant mass recorded
compound decomposes further (heated too much) -> heat gently, slowly, removing from heat periodically
