CPAC A1: finding the waters of crystallisation Flashcards
1
Q
METHOD
A
- weigh an empty clean crucible and lid
- (weighed by difference) add mass of hydrated salt
- heat strongly with a bunsen burner for a few minutes
- cool
- weigh crucible and contents
- repeat heating and weighing until constant mass
2
Q
why until constant mass
A
reaction is complete; all water evaporated
3
Q
why must crucible be dry
A
- if crucible wet, mass lost too large due to extra water lost when heating
4
Q
why use a lid on the crucible
A
- loose to allow gas to exscape
- but prevents loss of solid from crucible
5
Q
why not use small amounts of solid
A
percentage uncertainties too high
6
Q
if results are accurate …(in terms of uncertantes)
A
- percentage error (diff between your value and real value) is less than or equal to percentage uncertainty (calculted from the equipment)
7
Q
how to make data more precise (lower % uncertainty)
A
use a larger mass
8
Q
how to process data
A
- empirical formula calc with mass of solid and water
