Practicals

Question 1

RP1: Volumetric solution
Why is weighing boat reweighed?

Answer 1

To ensure accurate mass of solute added

Question 2

RP1: Volumetric solution + titration
What is done to ensure there is a uniform concerntration of solution?

Answer 2

Invert the volumetric flask a few times

Question 3

RP1: Volumetric solution + titration
Why are rinsings added?

Answer 3

To ensure all moles of solution has been transfered

Question 4

RP1: Volumetric solution + titration
Colours of each indicator in alkali and acidic conditions

Answer 4

Methyl orange:
Acid- Red
Base- Yellow
Phenolphthalein:
Acid- Colourless
Base- Pink

Question 5

RP1: Volumetric solution + titration
Why is a conical flask used for titration?

Answer 5

Easy to swirl

Question 6

RP1: Volumetric solution + titration
Why can’t the inside of the burette be rinsed with water

Answer 6

This will affect the concerntration of alkali and affect the titre values

Question 7

RP1: Volumetric solution + titration
Why is it okay to rinse the volumetric flask with water?

Answer 7

The overall moles of acid will be the same

Question 8

RP2: Measurement of enthalpy change
Change to the experiment which will minimise heat loss

Answer 8

Use a good insulator as a cup

Question 9

RP2: Measurement of enthalpy change
What would decrease the percentage uncertainty

Answer 9

Increasing number of moles of reactants added

Question 10

RP3: Investigation into how the rate of reaction changes with temperature
Why are small amounts of the reactants used

Answer 10

To limit the amount of sulfur dioxide formed

Question 11

RP3: Investigation into how the rate of reaction changes with temperature
Why isnt the experiement done between 1-10 degrees

Answer 11

Reaction would take too long

Question 12

RP4:Testing for anions and cations
Flame test colours
Lithium
Sodium
Potassium
Calcium
Barium
Copper

Answer 12

Lithium: Red
Sodium: Yellow
Potassium: Lilac
Calcium: Orange/red
Barium: Green
Copper: Blue/green

Question 13

RP5: Oxidation of alcohols under reflux and to form aldehydes

Methods of making sure aldehyde separated is pure.

Answer 13

Heat below boiling point of carboxylic acid and alcohol ensuring they don’t evaporate.

Question 14

RP5: Oxidation of alcohols under reflux and to form aldehydes

Why might a ketone sample collected be impure?

Answer 14

The alcohol may have not oxidised completely

Question 15

RP7: Measuring rate of reaction
Why is sodium hydrogencarbonate added before titration

Answer 15

To neutralise any remaining acid catalyst
Ensuring the reaction has stopped

Question 16

RP7: Measuring rate of reaction
How to stop a reaction which does not use an acid catalyst

Answer 16

Cool/ quench it

Question 17

RP8: Measuring EMF of electrochemical cell
What 2 solutions can be used in the salt bridge?

Answer 17

Aqueous silver nitrate or potassium chloride

Question 17

RP8: Measuring EMF of electrochemical cell
What 2 solutions can be used in the salt bridge?

Answer 17

Aqueous silver nitrate or potassium chloride

Question 18

RP8: Measuring EMF of electrochemical cell
How to tell if positive vs negative electrode

Answer 18

Positive: Removes electrons e.g electrons being taken in
Negative: Electrons being released e.g species being oxidised

Moves from negative to positive

Question 19

RP8: Measuring EMF of electrochemical cell
Suggest why cells cannot be recharged

Answer 19

Reaction isnt reversible

Question 20

RP8: Measuring EMF of electrochemical cell
Why does EMF of cells drop after time

Answer 20

Eventually will discharge and reagents used up

Question 21

RP8: Measuring EMF of electrochemical cell
How to maintain constant EMF in fuel cells

Answer 21

Maintain constant concerntration of reactants

Question 22

RP8: Measuring EMF of electrochemical cell
Explain how salt bridge provides electrical connection

Answer 22

Contains mobile ions

Question 23

RP8: Measuring EMF of electrochemical cell
Suggest why recyharging of lithium cell may produce CO2

Answer 23

Energy to recharge from power stations

Question 24

RP9: Titration curves How to select an indicator for a titration

Answer 24

Repeat with multiple indicators Pick an indicator which changes colour rapidly at the equivalence point

Question 25

RP9: Titration curves Why do you have to take funnel out of burette before titration?

Answer 25

Could produce droplets which would affect titre values

Question 26

RP9: Titration curves Suggest a source of error when using a burette to carry out titrations

Answer 26

Air bubble may form- affecting titre values

Question 27

RP9: Titration curves Suggest how washing the sides of conical flask improves accuracy of titre

Answer 27

Ensures all reagents able to mix Makes sure any reagents on the side are included in reaction mixture

Question 28

RP9: Titration curves Explain why adding water to conical flask doesn't affect titre values

Answer 28

Moles of acid remains the same

Question 29

RP9: Titration curves Method for calibrating PH probe

Answer 29

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

Question 30

RP9: Titration curves Suggest a way of improving accuracy approaching equivalence point

Answer 30

Add acid/ base dropwie and swirl

Question 31

RP10a: Production of asprin and Purification of soluble crystals Process of purification of asprin

Answer 31

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

Question 32

RP10a: Production of asprin and Purification of soluble crystals Why is solution dissolved in minimum volume of hot solvent

Answer 32

So that solution is saturated and solution will form on cooling

Question 33

RP10a: Production of asprin and Purification of soluble crystals Why is suction filtering used

Answer 33

This speeds up filtration

Question 34

RP10a: Production of asprin and Purification of soluble crystals Why are crystals washed with cold solvent

Answer 34

To remove any soluble impurities

Question 35

RP10a: Production of asprin and Purification of soluble crystals How to determine melting point

Answer 35

Add sample to a capillary tube attached to a thermometer in some heating oil Heat slowly near melting point

Question 36

RP10a: Production of asprin and Purification of soluble crystals How do impurities affect melting point

Answer 36

Lower melting points Melts over a range of values

Question 37

RP10a: Production of asprin and Purification of soluble crystals Industrial advantages of using ethanoic anhydride over ethanoyl chloride

Answer 37

Cheaper Reacts less vigourously Doesnt produce HCl gas

Question 38

RP10a: Production of asprin and Purification of soluble crystals Safety precaution when using hot ethanol solvent

Answer 38

Heat below BP of ethanol Dont heat under a naked flame

Question 39

RP10a: Production of asprin and Purification of soluble crystals Purpose of adding cold solvent

Answer 39

To remove soluble impurities

Question 40

RP10B: Preparation of a pure organic liquid Purifying an organic liquid method

Answer 40

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

Question 41

RP10B: Preparation of a pure organic liquid Why is sodium hydrogencarbonate added

Answer 41

To help the organic and aqueous layers separate

Question 42

RP10B: Preparation of a pure organic liquid Why is anhydrous sodium sulfate added

Answer 42

It is a drying agent

Question 43

RP10B: Preparation of a pure organic liquid Why is tap of separating funnel opened periodically

Answer 43

To reduce pressure buildup as CO2 gas is produced

Question 44

RP10B: Preparation of a pure organic liquid Why is anhydrous calcium chloride a good drying agents

Answer 44

It doesnt react with any compounds in the mixture

Question 45

RP10B: Preparation of a pure organic liquid How do anti-bumping granules prevent bumping

Answer 45

Prevent formation of large bubbles

Question 46

RP10B: Preparation of a pure organic liquid Why is an electric heater used in hydrolysis of esters

Answer 46

Ethanol is a product which is flammable

Question 47

RP10a: Production of asprin and Purification of soluble crystals Loss of yeild means in aspirin process

Answer 47

Crystals lost when filtering/ washing Some products remain in solution Other side reactions occuring