moles Flashcards
define molar mass
the mass in g, per mole of a substance (gmol-1)
define a mole
the amount of a substances containing as many particles as there are exactly 12 grams of carbon in carbon-12
define molar gas volume
the gas volume per mole of a substance. This is 24.0 dm3mol-1 at room and temp and pressure
define avogodros constant
the number of particles per mole of a substance (6.02x10^23)
define relative atomic mass
the weighted mean of mass of an atom compared with 1/12th the mass of an atom of Carbon-12
define relative molecular mass
the weighted mean mass of a simple covalent molecule compared with 1/12th of the mass of an atom of carbon-12
formula for number of particles
Na x moles
particles can be atoms ions or molecules
whats the standard size for a beaker?
250cm3
what does continuous monitoring give?
a rate
what does a concentrated solution contain?
a large amount of solute per dm3
what does the concentration give?
an accurate indication of the amount in moles of solute thats dissolved in a volume (1dm3)of the solution
given conc and volume in dm3, whats the formula for mole?
conc x volume
given conc and volume in cm3, whats the formula for mole?
c x v/1000
how to convert from gdm-3 to moldm-3?
divide by the Mr
define standard solution?
solutions of a known concentration
what would you need to do in order to make up a given volume of a solution with a precise conc?
-work out the amount of moles of the solute required
-calculate the mass needed for the chosen volume of water
what 2 ways can standard solutions be made by?
- dissolving a solid to form a solution of known concentration
- diluting a solution to form a solution of known concentrations
what glasswear are standard solutions prepared in?
volumetric flasks
method to prepare a standard solution
- accurately weigh solid in weighing boat (using mass by difference method)
- transfer solid to a 50cm3 beaker and dissolve solid fully with distilled water
- transfer solution to 250cm3 volumetric flask. rinse beaker with distilled water and add rinsings
- fill flask with distilled water until the bottom of the meniscus lines up exactly with the 250cm3 graduation mark. use a dropping pipette when near
- invert flask several times to mix fully
when making a standard solution, why is it important to add rinsings of weighing boat?
ensure all solution successfully transferred to volumetric flask
if not, would result in a lower concentration
whats the importance of lining the bottom of the meniscus up with the graduation mark?
if meniscus goes above graduation mark, the volume will be greater and conc will be less
if meniscus is lower than the graduation mark, then volume is less and conc is greater
what is an acid-base titration a type of?
volumetric analysis
what signifies the end point?
change in colour
what can be assumed of an end point in an acid-base titration?
moles of H+ ions from the acid = moles of OH- ions from the alkali
before the titration how should you prepare glass wear?
washing and conditioning
whats the formula for % uncertainty in titre
( uncertainty/ mean titre ) divide readings taken
(2 normally)
suggest errors when making a standard solution which would result in solution in being less concentrated?
-not rinsing mass boat and adding the rinsings
-conical flask washed, rinsed but not dried fully
