Elements of life Flashcards
(7 cards)
techniques and procedures for making soluble salts by reacting acids and a solid base
Solid bases may be:
* carbonates - will effervesce because they produce CO2 when reacting with acids. In
this case you continue adding the solid carbonate one spatula at a time, until there is
no more effervescence.
- metal oxides – in which case you continue adding the solid metal oxide one spatula at
a time, until no more will dissolve - add spatulas of the base to the acid in a beaker, until…. (see above)
- filter out the excess base
- pour the filtrate into an evaporating dish
- heat over a Bunsen burner until crystals start to form
- pick out the crystals
- dry to constant mass
techniques and procedures for making soluble salts by reacting acids and alkalis
use a volumetric pipette to transfer 25.0 cm3 of the alkali to a conical flask.
* Add a suitable indicator
* Add the acid from the burette until the end point is reached.
* Repeat until you have 2 concordant results and calculate the mean titre
* Repeat the procedure without an indicator. The volume of acid added should be the
mean titre
* pour the contents of the flask into an evaporating dish
* heat over a Bunsen burner until crystals start to form
* pick out the crystals
* dry to constant mass
techniques and procedures for making insoluble
salts by precipitation reactions
- mix the 2 solutions in a beaker or conical flask
- filter out the precipitate that is formed
- wash the precipitate with distilled water
- dry to constant mass
technique for drying to constant mass:
- place the solid on a watch glass and record the mass
- heat in an oven (set below the melting point of the solid) for 10 minutes
- remove the watch glass, allow it to cool, and reweigh
- Return to the oven and repeat the procedure until the mass does not change between
weighing’s (indicating that all the water/solvent has been driven off)
thermal stability of the carbonates, solubilities of hydroxides and carbonates experiments:
- add calcium hydroxide to distilled water to form limewater
- Stir and filter out the excess solid
- Crush the carbonates to a fine powder in a pestle and mortar
- Heat separately, timing how long it takes to turn the lime water milky
what are the control variables?
- Use same no of moles of each carbonate
- Use same conc and vol of limewater
- Heat with same strength flame, same distance
Observations:
- Less thermally stable carbonate will take less time for the limewater to turn milky
- Thermal stability increases down group, so CaCO3 would take longer to
decompose than MgCO3
