3.1.2 Amount of Substance Knowledge Flashcards
define Avogadro’s Constant
number of atoms in 12g of 12C
how do you calculate the number of particles?
Number of Particles = Moles x Avogadro’s Constant
how do you calculate relative atomic mass?
average mass of one atom of element / 1/12th the mass of a C12 atom
how do you calculate relative formula mass?
average mass of one molecule / 1/12th the mass of a C12 atom
what is the difference between relative formula and relative molecular mass?
Relative formula mass is used for ionic compounds because, strictly speaking, they don’t exist as simple molecules. Relative molecular mass and relative formula mass can both be calculated and used in the same way.
how do you calculate the number of moles?
moles (mol) = mass (g) / molar mass (g/mol)
how do you calculate concentration?
concentration (mol dm^-3) = moles (mol) / volume (dm^3)
how many cm^3 are in dm^3?
1000
what is the purpose of a titration?
to use one chemical solution of a known concentration (a standard solution) to determine the concentration of another by reacting them together
what are concordant results?
within 0.1cm^3 of each other
what are the Steps to make up a Standard Solution?
- Stage 1: transfer known mass of solid
- weigh sample bottle containing solid on 2 d.p. balance
- transfer to beaker and reweigh empty sample bottle
- record difference mas; this is = mass of solid
- Stage 2: dissolve in water
- add distilled/deionised water
- stir with glass rod or swirl
- until all solid has dissolved
- Stage 3: Transfer, washing, and agitation
- Transfer to volumetric/graduated flask using funnel with washings
- make up to 250cm^3/mark with water
- shake/invert/mix
what 3 things can be done to increase the accuracy of a titration?
- Remove any air bubbles from the burette tap
- Remove the funnel used to fill the burette before starting the titration
- During the titration, swirl the conical flask and rinse the walls of the conical flask with distilled water
why should you Remove any air bubbles from the burette tap in a titration?
otherwise, the volume of the air bubble will be counted in the burette reading, resulting in a greater titre
why should you Remove the funnel used to fill the burette before starting a titration?
to prevent any further liquid from entering the burette
why should you swirl the conical flask and rinse the walls of the conical flask with distilled water during a titration?
- to ensure all reactants mix and no reagent is left unreacted on sides of flask.
- Doesn’t change the number of moles in conical flask, so has no adverse effect on titration.
