Practical / 6 Markers

Titration

• rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)

• pipette 25 cm' of alkali into conical flask

• touch surface of alkali with pipette (to ensure correct amount is added)

• adds acid solution from burette

make sure the jet space in the burette is filled with acid

• add a few drops of indicator and refer to colour change at end point

• phenolphthalein [pink (alkali) to colourless (acid): end point pink colour just disappears] [use if NaOH is used]

• methyl orange [yellow (alkali) to red (acid): end point orange]
  [use if HCl is used]

• use a white tile underneath the flask to help observe the colour change

• add acid to alkali whilst swirling the mixture and add acid dropwise at end point

• note burette reading before and after addition of acid repeats titration until at least 2 concordant results are obtained- two readings within 0.1 of each other

Calorimetry (enthalpy)

washes the equipment (cup and pipettes etc) with the solutions to be used dry the cup after washing

put polystyrene cup in a beaker for insulation and support

Measure out desired volumes of solutions with volumetric pipettes and transfer to insulated cup

• clamp thermometer into place making sure the thermometer bulb is immersed in solutior measure the initial temperatures of the solution or both solutions if 2 are used. Do this every minute for 2-3 minutes
  At minute 3 transfer second reagent to cup. If a solid reagent is used then add the solution to the cup first and then add the solid weighed out on a balance.

• If using a solid reagent then use 'before and after' weighing method stirs mixture (ensures that all of the solution is at the same temperature)
  Record temperature every minute after addition for several minutes

Purifying an organic liquid

• Put the distillate of impure product into a separating funnel wash product by adding either sodium hydrogencarbonate solution, shaking and releasing the pressure from CO, produced

Saturated sodium chloride solution

Allow the layers to seperate in the funnel, and then run and

• Run the organic layer into a clean, dry conical flask and add three spatula loads of drying agent (e.g. anhydrous MgSO4/CaCl2), to dry the organic liquid. When dry the organic liquid should appear clear

• The layer with lower density will be the upper layer (usually organic layer)

• Carefully decant the liquid into the distillation flask

• Distil to collect pure product

Water of crystallisation

The water of crystallisation in calcium sulfate crystals can be removed as water vapour by heating as shown in the following equation.

CaSO, XH2O(s) → CaSO,(s) + xH,0(g)

Method.

• Weigh an empty clean dry crucible and lid .

• Add 2g of hydrated calcium sulfate to the crucible and weigh again

• Heat strongly with a Bunsen for a couple of minutes

• Allow to cool

• Weigh the crucible and contents again

• Heat crucible again and reweigh until you reach a constant mass