Core Practicals

Question 1

What is the first stage as to work out the composition of ink?

Answer 1

• simple distillation to try and remove the solvent assuming that it has a lower boiling point
• pour sample into distillation flask
• gradually heat and the solvent should evaporate and pass into the condenser where it cools and condenses
• leaves the ink in the flask

Question 2

What is stage 2 of finding out the composition of ink?

Answer 2

Paper chromatography

• draw a line near the bottom in pencil (insoluble so won’t dissolve with the solvent)
• put the solvent into the beaker so it is below the line so ink doesn’t dissolve into the water but rather up the page
• put watch glass on top so it doesn’t evaporate
• solvent moves up the paper and as the dyes dissolve they will too
• you will see the different chemicals separate pit

Question 3

How to measure RF value?

Answer 3

-distance moved by solute/distance moved by solvent

Question 4

How do you do electrolysis of copper sulphate with graphite electrodes?

Answer 4

• copper sulphate contains four different ions (Cu2+,SO42-, H+ and OH-)
• place copper sulphate solution into the container and place the electrodes in making sure the circuit is complete

Question 5

With graphite electrodes what is made at the cathode?

Answer 5

Copper as it is less reactive than hydrogen
-visible costing on the electrode
Cu2+ + 2e- — Cu

Question 6

With graphite electrodes what is made at the anode

Answer 6

Oxygen and water as there are no halides present
-you should see bubbles and oxygen gas forming
4OH- — O2 + 2H20 + 4e-

Question 7

How do you do electrolysis with copper electrodes?

Answer 7

• pit copper sulphate solution in the container and put the electrodes in making sure the circuit is complete
• leave for at least 30 minutes to see a considerable change in mass

Question 8

What happens to the anode and cathode with copper electrodes?

Answer 8

• mass of anode will decrease. This is because copper is oxidised and looses electrons (Cu—Cu2+ +2e-)
• mass of cathode will increase as electrons are deposited and offered to nearby copper ions (Cu2+ + 2e- —Cu)

Question 9

How can you measure the change is mass?

Answer 9

• measure mass of electrodes before
• dry and measure them again at end of experiment
• if you increase the current you will increase rate of electrolysis so greater change j. Mass

Question 10

What are the first 3 stages of titration?

Answer 10

• using a pipette measure a set volume of the alkali into a flask and add a few drops of phenolphthalein indicator to turn it purple
• fill a Burette with a known concentration and volume of acid
• use the burette to add the acid to the flask a little at a time, swirling regularly, go slower when you think it’s almost neutralised

Question 11

What are the last three stages of titration?

Answer 11

• the indicator changes colour when all the alkali has been neutralised (should turn colourless)
• record the volume of acid used to neutralise it (the titre)
• repeat to ensure you get similar results and then calculate and mean

Question 12

What should you do before the actual titration experiment?

Answer 12

• do a rough titration so you have a rough idea of how much is needed to neutralise it.
• this means you can go slower and more precisely in the real thing when you get closer
• do it on a white tile so colour change more obvious and do it at eyelevel

Question 13

What is the method to see SA’s effect on rate?

Answer 13

Set up a conical flask, bung and gas syringe

• place a set volume of hydrochloric acid in a flask and add a set mass of marble chips)
• measure the volume of gas produced taking readings at regular time intervals
• repeat with same mass and concentration but finer crushed up chips and then with dissolved powder
• plot graph (time on X and volume on Y)

Question 14

What are the first 3 stages to see how reaction changes with temperature?

Answer 14

• measure out a fixed volume of sodium thiosulphate and hydrochloric acid
• use a water bath to gently heat both solutions to the desired temp before mixing them
• mix solutions in a conical flask and place over a black cross on a piece of paper that is visible through the solution

Question 15

What are the last 3 stages to see how reaction changes with temperature?

Answer 15

• watch the black mark disappear through the cloudy yellow silver and time how long it takes till it is no longer visible
• repeat at different temps with the same controls

Question 16

Test for anions and cations

Answer 16

SEE QUALITATIVE ANALYSIS

Question 17

What are the first 2 stages of burning alcohol to heat up water?

Answer 17

-put a set volume of alcohol into a spirit burner and measure the mass of the burner and the fuel using a mass balance
(These can be hazardous so make sure to wear gloves and glasses)
-measure a set volume of distilled water into a copper calorimeter

Question 18

What are the third and fourth stages of burning alcohol to heat up waters?

Answer 18

• insulate the calorimeter using a drought excluded and cover with an insulating life after placing thermometer in (minimises energy loss to surroundings)
• take initial temp of water and then place burner underneath and light the wick
• stir the water throughout using thermometer so heat is evenly dispersed and when heat from the thunder has made the temp of the water rise 20° blow the spirit burner out

Question 19

What are the last two stages of burning alcohol to heat up water?

Answer 19

• immediately reweigh the burner and fuel
• repeat using other alcohol but keep controls constant
• best fuel is one that is burnt less (smallest change in mass)

Question 20

What are the first two stages of making a soluble salt using an acid and insoluble base?

Answer 20

• react acid that contains one of the ions you want in the salt with an insoluble bad that contains the other ion you need
• heat the acid in a water bath that speeds up the reaction (do in a fire cupboard to avoid releasing acid fumes)

Question 21

What are the next two stages of making a soluble salt?

Answer 21

• add the base and the two will react to produce a soluble salt and water
• you will when the base is in excess and all the acid neutralised because the excess solid will just sink to the bottom
• filter of the excess so solution containers only salt and water
• heat the solution gently to slowly evaporate off some of these the water, leave to cool and salt to crystallise
• filter of solid and leave to dry

Question 22

How do you investigate neutralisation?

Answer 22

• measure a set volume of dilute hydrochloric acid into a conical flask
• measure a fixed mass of calcium oxide using a mass balance and mix
• wait for the base to react completely and record PH
• repeat until all the acid has reached (you will see unreacted calcium oxide at the bottom of the flask
• plot a graph to see how PH changes with mass added