Specifications

Core Practicals

Core Practical 1

Investigating the composition of inks

Introducing the Practical

This core practical is in two parts; a simple chromatography practical to obtain a chromatogram of dyes in ink and using simple distillation apparatus to separate pure water from ink.

  

It needs to cover usage of a Bunsen burner, methods used in chromatography and distillation and safety of handling liquids.

Risk Assessment

As a general rule, eye protection (goggles) must be worn for all practicals.

  

This risk assessment is provided as an example only, and you must perform your own risk assessment before doing this experiment.

Apparatus

Each group will need:

  • a conical flask with a two‐hole bung with a thermometer and delivery tube

  • test tube

  • beaker (250 or 400 ml)  

  • crushed ice

  • Bunsen burner  

  • tripod  

  • gauze  

  • heat‐resistant mat

  • ink  

  • antibumping granules

  • 250 ml beaker

  • chromatography paper  

  • a splint or pencil or glass rod/paper clips

  • selection of different coloured marker pens or felt‐tip pens

  • solvent (water)

Experiment Set-up

Method

Simple Distillation

  1. add about 20 ml of ink to a conical flask

  2. connect the flask to a delivery tube and set up the apparatus as shown above

  3. heat the flask using a Bunsen burner until boiling, then reduce the heat for a gentle boil

  4. collect a small sample of the distilled solvent, then turn the Bunsen Burner off

Paper Chromatography

  1. draw a pencil line across chromatography paper (about 1 cm above the bottom)

  2. use a pipette, or capillary tube, to add small spots of each ink to the line on the paper (equally spread across the paper)

  3. place the paper into a container with a suitable solvent (e.g. water) in the bottom - making sure the pencil line is above the water line

  4. allow the solvent to move through the paper, but remove the chromatogram before it reaches the top

  5. allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent

Results and Analysis

Simple Distillation

What is the appearance of the distilled solvent?
Explain any difference in the appearance of the solvent and ink.

At what temperature did the thermometer read as your solvent condensed?
How does this compare with the boiling points of common solvents like water, ethanol or propanol?

Paper Chromatography

Calculate the Rf value of each spot.
Compare the Rf values/colours of each spots in the different inks - what are the similarities and differences?

Exam Question and Model Answer

A new type of waterproof pen has just been released, and it contains ink that is insoluble in water. A company suspects it may be a copy of their pen's ink. Describe how they should use paper chromatography to identify whether the inks are the same.

[6 marks}

Level 1 (1-2 marks)

Place a spot of the inks on the paper, and place the paper in a beaker with water (not covering the pencil line).
Hang the piece of paper in a beaker and let the water rise through the paper.

Level 2 (3-4 marks)

Place a spot of the new pen's ink from the pen on chromatogaphy paper, and place a spot of the original ink on there too.
Hang the piece of paper in a beaker, and add a small amount of solvent (not water, e.g. ethanol) as to not cover the pencil line.
Allow the solvent to rise up the paper.

Level 3 (5-6 marks)

Draw a line (in pencil) across a piece of chromatography paper, about 1 cm above the bottom.
Place a spot of the new pen's ink from the pen on the pencil line, and place a spot of the original ink on the line.
Hang the piece of paper in a beaker, and add a small amount of solvent (not water, e.g. ethanol) as to not cover the pencil line.
Allow the solvent to rise up the paper.
Measure how far the solvent moved, as well as each spot on the chromatogram, and calculate the Rf values of each spot.
If the Rf values match, then the ink is a copy.

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