stochiometry (1.4-1.5) Flashcards
whats the standard unit of amount of susbtance
the mole
what does the mole contain
exactly the number of elementary given by the avogrados constant (6.0 X 10ˆ23)
what are the mass of an atom compared to
carbon 12 and are expressed as relative atomic mass Ar and relative formula mass Mr
whats the empircal formula
simplest whole ratio of atoms of each element present in compound
whats molecular formula
ratio shows actual amount of atoms of each element present in that compound
how do you prepare a standard solution
-weigh weighing boat, note mass
-add about 2g acid, note mass
-add acid to washed beaker
-reqeigh the boat and wirte the weight
-add 50ml distileled water to beaker stir to dissolve crystals crush them-put a washed funne into washed volumetric flask and carefully pour the acid down stirring rod into funnel do not lose any acid
-return rod to beaker and add 50 ml to rinse beaker and add to flask rinse rod and funnel, do not go over 250ml
-put lid into flask secure base and shake
convert from cm cubed to dm cubed
cm-dm = /1000
how can you express conecntration
[ ] square brackets
describe how to carry out an acid based titration
-rinse buretter with small amount of acid, throw to waste
-fill burette with acid until bottom of miniscus 0.00 line
-rinse pipette with base/ alklai
-use pump and volumetric pipetter to pipette 25 ml of base into conical flask
-add a few drops of indicator eg.phenolpthalein indicator
-add acid washing and swirling until you achieve a pale pink color
-record volume on burette
-wash out flask and repeat
-achieve until you have 2 concordant results (within 0.2)
how do you calculate uncertaintys
divide the uncertainty of aparatus by weight or value of measured eg mass times by 100% and all uncertaintys, and calculate the percentage difference from og value
what does avogrados law state
equal volumes of all gases under same conditions (temp and pressure) contain euqal numbers of mlecules (22.7 dm cubed molˆ-1)
equation relating gases and moles
volume= mol * 22.7
whats the mr of a molecule
the sum of all the relative atomic masses
whats the Ar
atomic masses of the constituent elements in the molecule
what are the standar conditions
273K, 100KPa
what is an ideal gas
-moving particles with negible volume and intermoecular forces
-all collisions between particles are considered elastic and frictionless( no energy loss in motion or collision)
-moelcules constantly moving in random directions with distribution of speeds
-molecules of gas are indistinguishible small hard spheres that are point-like
why are gases no ideal
-some factors such as gravity will cause particles to have variable concentrations
-particles have intermolecular forces attractive and electrons are repulsive
what causes the attractive forces between the particles to be negiligible
great seperation of the particles
what happens to pressure when volume is halved
doubles the collisions, doubles pressure
what happens when double numb of moles to pressure
double the numb of collisions, doubles pressure
what happens when double temp to pressure
double temp you double the KE and therefore double the collisions and the pressure
describe graph of p against v
they are inversely porportional
when its p vs 1/v then its a positive correlation, directly porportional
describe graph of v against T
directly porportional
describe graph of T against P
directly porportional
what are characterisitcs good to be used as standard solutions
it has high relative molecular mass- reduces our uncertainty
it is soluble- all dissolve
it is stable in the atmosphere (non-hygroscopic and unreactive)- non-hygroscopis= does not absorb water from atmosphere unreactive
accuracy
all results are equal or close to true value, results which are inaccurate are because of random erros eg incorrect use of equipment, human errors
precise
very close to average, can be inaccurate because of systematic errors eg. un calibrated balance
