Chemistry practical skills

Method;

1.     Add a measured amount of acid to a conical flask.

2.     Add a ***** of metal to the conical flask and place a bung firmly on top.

3.     Start the timer.

4.     Record the volume of gas in the gas syringe every 15 seconds in a results table.

5.     Repeat with different concentrations of acid.

Iodine clock method;

1.     Add measured amounts of H_2­­SO₄, distilled water, KI, Na₂S_2­­O₃ to a 250cm³ conical flask.

2.     Add a few drops of starch indicator.

3.     Stir in a measured amount of H₂O₂ and start the timer.

4.     Stop the timer when the mixture turns blue/black. Record the time in a table

5.     Repeat the experiment in a clean dry flask, but with different volumes (conc.) of KI and H₂O.

6.     Analyse results. Human error can be decreased by use of colorimeter.

Theory;

Enough I_2­ formed to overcome specific barrier of Na_2­S₂O­₃, which reacts immediately after that point with the starch indicator.

Method;

1.     Pipette 25cm³ of ethanoic acid into a clean beaker.

2.     Rinse a burette with NaOH and then fill it with NaOH.

3.     Rinse a pH probe with distilled water and clamp it so that the bulb is fully immersed in the acid.

4.     Record the pH in a table

5.     Add exactly 2.0cm³ of the NaOH solution to the acid. Stir and take pH reading.

6.     Add the NaOH solution in 2.0cm³ portions until 40cm³, taking a pH reading each time.

Method;

1.     The prepared sample is dissolved in a minimum volume of hot solvent [Dissolves soluble impurities].

2.     The solution is filtered while still hot, using fluted filter paper [Filtrating insoluble impurities].

3.     The filtrate is cooled in ice to form crystals.

4.     The crystals are collected by suction filtration [Removes soluble impurities].

5.     The crystals are washed cold water (solvent).

6.     The crystals are left to dry.

Method;

1.     Crush the sample with a spatula to form a powder.

2.     Put the solid into a melting point tube (sealed at one end) to a depth of 0.5cm (approx.).

3.     Heat the oil, with the tube in, gently and observe the temperature when the solid melts (sudden change in pure samples).

4.     Allow the apparatus to cool and repeat with another sample of solid.

5.     Compare melting point of solid to known data.

Method;

1.     Wash the distillate with Na₂CO₃ solution in separating funnel removing acidic impurities.

2.     The pressure must be released now and then to let out CO_2­ produced.

3.     Repeat until no more gas is produced.

4.     The aqueous layer is discarded and water is added to wash organic layer.

5.     Run out denser aqueous layer [This removes soluble impurities such as sodium salts and soluble organic impurities].

6.     The aqueous layer is run out again and removed. Aqueous CaCl₂ is added to remove ethanol.

7.     Pour organic layer into a beaker and add solid CaCl₂ to remove water. Decant clear liquid into a flask and distil.

Method;

1.     Use a pencil to draw a line 1cm above the bottom of the TLC plate.

2.      Use capillary tube to apply a tiny drop of solution to a spot on the line.

3.     Add about 10cm³ of solvent to a suitable container with lid (prevents evapouration).

4.     Place the TLC plate in the container, making sure the level of the solvent is below the spotting line.

5.     When the level of the solvent reaches about 1cm from the top of the plate, remove it and mark the solvent front.

6.     Allow plate to dry and place under UV lamp to see spots.

[Rf value = Distance travelled by spot/ Distance travelled by solvent]

Method;

1.     Take a piece of copper and a piece of zinc, and clean with sandpaper (removing oxide layer) and then wipe with propanone (removing grease).

2.     Set up apparatus with a piece of filter paper soaked in NaCl (unreactive) as a salt bridge.

3.     Connect up the two half-cells using crocodile clips.

4.     Record the reading on the voltmeter.

5.     Repeat the experiment using different metal/solution half-cells.