EMPA Flashcards
How can percentage errors be reduced?
Use larger quantites (volumes, masses etc)
Use more precise equipment
How can procedural errors be reduced when making a standard solution?
- Rinse out weighing bottle with distilled water and add this to the volumetric flask
- Ensure the bottom of the meniscus is level with the graduated mark
- Invert the flask many times to ensure complete mixing of the solution
How can procedural error be reduced when carrying out a titration?
- Rinse out pipette and burette with the solutions that are going in them.
- Swirl the flask during the titration
- Rinse the side of the flask with distilled water
- Add the solution in the burette dropwise near the end point
What is the setup for collecting a gas?
What are the issues with the methods of collection gases?
Gas syringe:
- Syringe can stick due to the damp gas
Collection over water:
- Some gas dissolves in the water
Both:
- Some of the gas escapes before the bung is inserted
How can insoluble impurities be removed from a sample?
- Dissolve the sample in a suitable solvent
- Filter the mixture (rinse the residue on the filter paper with a little solvent)
How can dry crystals of x be produced from the solution?
- Put the solution in an evaporating basin and heat gently
- Evaporate half and then allow the rest to evaporate at room temperature
- Transfer the crystals on filter paper and wash with ice cold water
- Place the filter paper in an oven to dry out the crystals
What precautions should be taken if chemical x is an irritant/corrosive/toxic?
Wear gloves/goggles
Avoid contact with the skin
What precautions should be taken if x is flammable/volatile?
Avoid naked flames
Why is recrystallisation necessary?
- Chemicals may be impure
- Chemicals may decompose over time to form other compounds
- The reaction may not go to completion
How is a chemical purified by recrystallisation?
- Dissolve in a minimum volume of hot water
- Filter solution hot
- Cool filtrate in ice
- Collect crystals and wash with cold water
When carrying out a recrystallisation, why is a minimum volume of hot water used?
- To obtain a saturated solution
- To increase yield (reduce amount left in solution)
- Enable crystallisation on cooling
When carrying out a recrystallisation, why is the solution filtered hot?
- To remove insoluble impurities
- To prevent crystals forming during filtration
When carrying out a recrystallisation, why is the filtrate cooled in ice?
To increase the amount of crystals that are formed
When carrying out a recrystallisation, why are the crystals washed with cold water?
To remove soluble impurities
What is the setup for filtration under reduced pressure?
What is the setup for reflux?
What is the setup for distillation?
