Practical 2 - How big is an atom? Flashcards
Why is it important to calibrate the measuring cylinder?
Accurate volume measurements are essential for precise calculations.
Even slight errors in the measured volume can significantly affect the final estimation of atomic size.
Calibration ensures that each time you measure a volume, you are getting consistent, repeatable results.
Minimises systematic errors.
How do you calculate the density?
density (g/ml) = mass (g) / volume (ml)
How do you calculate the mass of a unit cell (g/unit cell)?
1/(6.022x10^23 (mol^-1) ) x atomic mass (g/mol) x atoms per unit cell (atoms/unit cell)
How do you calculate the volume of a unit cell (ml/unit cell)?
mass of unit cell (g) / density of metal (g/ml)
How do you convert cm^3/unit cell to pm^3/unit cell?
x 10^30
(because 1cm = 1x10^10pm)
How do you work out unit cell parameter in pm?
cube root volume (pm^3/unit cell)
How do you calculate the radius of a scc from the parameter?
a/2
How do you calculate the radius of a bcc from the parameter?
√3 a / 4
How do you calculate the radius of a fcc from the parameter?
a/√8
Limit the use of intensifiers and use…
comparators.
What should you always calculate at the end of the experiment?
% error
How do you calculate percentage error?
(|expected value - actual value| / actual value) x 100
List the potential errors for this experiment.
Used the wrong unit cell in calculations.
Calculation errors.
Rounding errors cause a large difference as stacking calculations.
Purity of metal.
Resolution of the balance.
Wet cylinder before adding metal.
Temperature of water changed during experiment - incorrect value for density.
How does the purity of the metal influence the value obtained for atomic radius?
Impurities affect the metal’s density and atomic arrangement, both of which are critical in calculations that determine atomic size.
