Practical

Question 1

Method for calculating the measurement of an enthalpy change.

Answer 1

Weigh out drying agent and record to a precise amount.

Place 25cm3 of deionised water into a polysterene cup and record initial temperature.

Start timer and record temp for first three minutes.

At the fourth minute, add first reagent and began recording in minute intervals at 5 minutes again.

Stir continuously as this occurs and a lid may prevent heat loss.

Question 2

Method to investigate the rate of reaction changes with temperature

Answer 2

Add 10cm3 of HCl to a test tube

Add 10cm3 of sodium thiosulfate to a test tube with a black X cross under it. Carefully insert thermometer and record initial temperature.

Add 1cm3 of acid to test tube and start stopcock.

Record time taken for X to disappear

Record final temperature and pour into sodium carbonate solution to prevent SO2

Do at different temperatyre by warming with a water bath

Question 3

How to distil a product from a reaction method

Answer 3

Acidify the potassium manganate(VII) solution combining a volume of a regular laboratory concentration with an equal volume of dilute sulfuric acid.

Pour the mixture into a pear-shaped/round flask, with a still head containing a thermometer.

Attached to a condenser with a ice cooled collecting vessel.

Add a few anti-bumping granules.

Heat the flask gently.

Collect sample at boiling point of the desired product.

The cooled collection vessel is essential to reduce evaporation of the product.

Question 4

Continuous monitoring method for rate of reaction

Answer 4

Add 50cm3 of 0.8 HCl to a conical flask.

Set up gas syringe equipment.

Add a 6cm strip of Mg ribbon to a conical flask, place the bung firmly on top of the flask.

Record volume of H gas every 15 seconds for 2.5 minutes.

Alter HCl concentration and repeat steps.

Question 5

How to preapre a medicine sample for TLC

Answer 5

Crush an aspirin tablet with pestle and mortar.

Transfer to a weighing boat or bottle.

Dissolve approx 0.1g of the powdered tablet in 0.5 cm of ethanol.

Repeat with other painkiller tablets.

Question 6

How to peform TLC

Answer 6

Prepare a beaker with a small quantity of solvent

On a TLC plate, draw a horizontal line at the bottom edge (in pencil)

Place a spot of pure reference compound on the left of this line, then a spot of the sample to be analysed to the right of the baseline and allow to air dry

Place the TLC plate inside the beaker with solvent and place a lid on top

Take out before solvent reaches the top and draw new pencil line

Question 7

Method of purifying an organic liquid

Answer 7

Put the distillate of impure product into a separating funnel

Add saturated sodium chloride solution

Allow layers to separate in funnel, and then run and discard the aqueous layer

Run the organic liquid into a clean, dry conical flask and add 3 spatula loads of drying agent

Carefully decant the liquid into the distillation flask

Distil to collect pure product

Question 8

How to recrysrallise an organic product to test boiling point

Answer 8

Dissolve the impure compound in a
minimum volume of hot (near boiling)
solvent

Hot filter solution through (fluted) filter
paper quickly.

Cool the filtered solution by inserting
beaker in ice.

Suction filtrate with a Buchner flask to
separate out crystals.

Wash the crystals with distilled water

Dry the crystals between absorbent
paper.