Practicals Flashcards
RP1: Volumetric solution
Why is weighing boat reweighed?
To ensure accurate mass of solute added
RP1: Volumetric solution + titration
What is done to ensure there is a uniform concerntration of solution?
Invert the volumetric flask a few times
RP1: Volumetric solution + titration
Why are rinsings added?
To ensure all moles of solution has been transfered
RP1: Volumetric solution + titration
Colours of each indicator in alkali and acidic conditions
Methyl orange:
Acid- Red
Base- Yellow
Phenolphthalein:
Acid- Colourless
Base- Pink
RP1: Volumetric solution + titration
Why is a conical flask used for titration?
Easy to swirl
RP1: Volumetric solution + titration
Why can’t the inside of the burette be rinsed with water
This will affect the concerntration of alkali and affect the titre values
RP1: Volumetric solution + titration
Why is it okay to rinse the volumetric flask with water?
The overall moles of acid will be the same
RP2: Measurement of enthalpy change
Change to the experiment which will minimise heat loss
Use a good insulator as a cup
RP2: Measurement of enthalpy change
What would decrease the percentage uncertainty
Increasing number of moles of reactants added
RP3: Investigation into how the rate of reaction changes with temperature
Why are small amounts of the reactants used
To limit the amount of sulfur dioxide formed
RP3: Investigation into how the rate of reaction changes with temperature
Why isnt the experiement done between 1-10 degrees
Reaction would take too long
RP4:Testing for anions and cations
Flame test colours
Lithium
Sodium
Potassium
Calcium
Barium
Copper
Lithium: Red
Sodium: Yellow
Potassium: Lilac
Calcium: Orange/red
Barium: Green
Copper: Blue/green
RP5: Oxidation of alcohols under reflux and to form aldehydes
Methods of making sure aldehyde separated is pure.
Heat below boiling point of carboxylic acid and alcohol ensuring they don’t evaporate.
RP5: Oxidation of alcohols under reflux and to form aldehydes
Why might a ketone sample collected be impure?
The alcohol may have not oxidised completely
RP7: Measuring rate of reaction
Why is sodium hydrogencarbonate added before titration
To neutralise any remaining acid catalyst
Ensuring the reaction has stopped
RP7: Measuring rate of reaction
How to stop a reaction which does not use an acid catalyst
Cool/ quench it
RP8: Measuring EMF of electrochemical cell
What 2 solutions can be used in the salt bridge?
Aqueous silver nitrate or potassium chloride
RP8: Measuring EMF of electrochemical cell
What 2 solutions can be used in the salt bridge?
Aqueous silver nitrate or potassium chloride
RP8: Measuring EMF of electrochemical cell
How to tell if positive vs negative electrode
Positive: Removes electrons e.g electrons being taken in
Negative: Electrons being released e.g species being oxidised
Moves from negative to positive
RP8: Measuring EMF of electrochemical cell
Suggest why cells cannot be recharged
Reaction isnt reversible
RP8: Measuring EMF of electrochemical cell
Why does EMF of cells drop after time
Eventually will discharge and reagents used up
RP8: Measuring EMF of electrochemical cell
How to maintain constant EMF in fuel cells
Maintain constant concerntration of reactants
RP8: Measuring EMF of electrochemical cell
Explain how salt bridge provides electrical connection
Contains mobile ions
RP8: Measuring EMF of electrochemical cell
Suggest why recyharging of lithium cell may produce CO2
Energy to recharge from power stations
RP9: Titration curves
How to select an indicator for a titration
Repeat with multiple indicators
Pick an indicator which changes colour rapidly at the equivalence point
RP9: Titration curves
Why do you have to take funnel out of burette before titration?
Could produce droplets which would affect titre values
RP9: Titration curves
Suggest a source of error when using a burette to carry out titrations
Air bubble may form- affecting titre values
RP9: Titration curves
Suggest how washing the sides of conical flask improves accuracy of titre
Ensures all reagents able to mix
Makes sure any reagents on the side are included in reaction mixture
RP9: Titration curves
Explain why adding water to conical flask doesn’t affect titre values
Moles of acid remains the same
RP9: Titration curves
Method for calibrating PH probe
Measure probe in buffered solution of varying PH
Rinse PH prove with deionised water inbetween
Plot a graph of PH of buffer against PH reading on probe
RP9: Titration curves
Suggest a way of improving accuracy approaching equivalence point
Add acid/ base dropwie and swirl
RP10a: Production of asprin and Purification of soluble crystals
Process of purification of asprin
Add minimum amount of hot solvent
Filter to remove any insoluble impurities
Cool solution and stir to recrystalise
Filter solution under reduced pressure (Buchner funnel)
Rinse product off with cold solvent
Allow product to dry- between absorbent paper
RP10a: Production of asprin and Purification of soluble crystals
Why is solution dissolved in minimum volume of hot solvent
So that solution is saturated and solution will form on cooling
RP10a: Production of asprin and Purification of soluble crystals
Why is suction filtering used
This speeds up filtration
RP10a: Production of asprin and Purification of soluble crystals
Why are crystals washed with cold solvent
To remove any soluble impurities
RP10a: Production of asprin and Purification of soluble crystals
How to determine melting point
Add sample to a capillary tube attached to a thermometer in some heating oil
Heat slowly near melting point
RP10a: Production of asprin and Purification of soluble crystals
How do impurities affect melting point
Lower melting points
Melts over a range of values
RP10a: Production of asprin and Purification of soluble crystals
Industrial advantages of using ethanoic anhydride over ethanoyl chloride
Cheaper
Reacts less vigourously
Doesnt produce HCl gas
RP10a: Production of asprin and Purification of soluble crystals
Safety precaution when using hot ethanol solvent
Heat below BP of ethanol
Dont heat under a naked flame
RP10a: Production of asprin and Purification of soluble crystals
Purpose of adding cold solvent
To remove soluble impurities
RP10B: Preparation of a pure organic liquid
Purifying an organic liquid method
Put mixture into separating funnel
Add sodium hydrogen carbonate
Allow layers to separate in the funnel
Run organic layer into conical flask and add drying agent
Distill product to make it entirely pure
RP10B: Preparation of a pure organic liquid
Why is sodium hydrogencarbonate added
To help the organic and aqueous layers separate
RP10B: Preparation of a pure organic liquid
Why is anhydrous sodium sulfate added
It is a drying agent
RP10B: Preparation of a pure organic liquid
Why is tap of separating funnel opened periodically
To reduce pressure buildup as CO2 gas is produced
RP10B: Preparation of a pure organic liquid
Why is anhydrous calcium chloride a good drying agents
It doesnt react with any compounds in the mixture
RP10B: Preparation of a pure organic liquid
How do anti-bumping granules prevent bumping
Prevent formation of large bubbles
RP10B: Preparation of a pure organic liquid
Why is an electric heater used in hydrolysis of esters
Ethanol is a product which is flammable
RP10a: Production of asprin and Purification of soluble crystals
Loss of yeild means in aspirin process
Crystals lost when filtering/ washing
Some products remain in solution
Other side reactions occuring
