Researching Chemistry pt 2 ✓ Flashcards
Gravimetric Analysis
What is Gravimetric analysis?
Gravimetric analysis is used to measure the mass of an element/compound in a substance. The substance is converted into a second substance that can be isolated and purified.
What is weighing by TARE?
Weighing by TARE allows a substances to be weighed directly, it is less accurate as any mass left in the weighing boat isn’t accounted for
What is weighing by Difference?
Weighing by difference allows a more accurate measurement as it gives an exact measurement of the substance in the reaction vessel
What is weighing accurately approximately?
Weighing accurately approximately is when the approximate mass of a substance is weighed, but the mass actually used is recorded accurately
What is Volatilisation?
Volatilisation is when a sample of substance is weighed and then heated to release the volatile product (ususally water) by evaporation
NOTE: Volatile means it evaporates easily
What is a Desiccator used for?
A desiccator provides a dry atmosphere, preventing moisture from being reabsorbed into a substance from the air
What is meant by heating to a constant mass?
Heating to a constant mass is when a substance is heated then cooled in cycles until the mass stays consistent (differing by no more than 0.002g), this ensures the volatile product is completely gone
What is Precipitation ?
Precipitation is when the precipitate (solid) is seperated from the filtrate (liquid).
The filtrate is then tested to ensure the reaction went to completition, the precipitate is washed and dried to constant mass, then weighed
What is Percentage yield?
Percentage yield is when the theoretical yield is compared to the yield actually produced in a reaction (actual yield)
What is the Actual yield of a reaction?
The actual yield is the mass of pure product that is obtained in a reaction
What is the Theorertical yield of a reaction?
The theoretical yield is the maximum mass that can be expected to be obtained in a reaction
Why is Percentage yield always under 100%? (3)
Percentage yield is always under 100% as:
- There is a loss of product (when transferring between containers/during recrystallisation/product evaporation)
- A side reaction may occur (side products reduce main product yield)
- Reaction may be reversible (Equilibrium will be reached and 100% conversion of reactants into products can’t happen)
What is Purification by Recrystallisation?
Purification by recrystallisation is when crude/impure crystals are heated in a solvent, filtered, cooled and then filtered off to produce pure crystals
What ensures recrystallisation is successful?
Successful recrystallisation is dependant on the choice of solvent
How can a suitable solvent for recrystallisation be determined? (3)
A suitable solvent must:
- Not react with the substance
- The substance must be very soluble in the hot solvent
- The substance must be insoluble in the cold solvent
