Chemistry PAG 3: Separation techniques

Combined Science PAG C3: Separation techniques

Suggested Activity 3: Kitchen chromatography

Instructions and answers for teachers and technicians

These instructions cover the learner activity section which can be found on page 10. This Practical activity supports OCR GCSE Chemistry and Combined Science.

When distributing the activity section to the learners either as a printed copy or as a Word file you will need to remove the teacher instructions section.

This is a suggested practical activity that can be used as part of teaching the GCSE (9-1) Gateway Science (A) and Twenty First Century Science (B) specifications.

These are not controlled assessment tasks, and there is no requirement to use these particular activities.

You may modify these activities to suit your learners and centre. Alternative activities are available from, for example, Royal Society of Biology, Royal Society of Chemistry, Institute of

Physics, CLEAPSS , SSERC and publishing companies, or of your own devising.

Further details are available in the specifications (Practical Skills Topics), and in these videos.

OCR recommendations:

Before carrying out any experiment or demonstration based on this guidance, it is the responsibility of teachers to ensure that they have undertaken a risk assessment in accordance with their employer’s requirements, making use of up-to-date information and taking account of their own particular circumstances. Any local rules or restrictions issued by the employer must always be followed.

CLEAPSS resources are useful for carrying out risk-assessments: (http://science.cleapss.org.uk).

Centres should trial experiments in advance of giving them to learners. Centres may choose to make adaptations to this practical activity, but should be aware that this may affect the Apparatus and Techniques covered by the learner.

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IntroductionThis is an activity that can be used to refresh learners’ knowledge of chromatography which is likely to have been studied at Key Stage 3 and prior. It could provide a hook to formally introduce concepts of stationary and mobile phase, calculation of Rf values and differential separation of substances with different mobile phases, e.g. by use of the OCR Suggested Activity 2 for the Practical Activity Group ‘Separation Techniques’ : http://www.ocr.org.uk/Images/323640-pag-activity-chemistry-separation-techniques-suggestion-2.doc.

As a ‘kitchen chemistry’ practical, this could also be set as homework for learners to use the food dyes they have at home, and then ask your learners to bring in their chromatograms. Ensure you provide clear instructions to your learners to seek permission from their parents/guardians to use household solvents before they carry out any work.

AimsTo investigate the different separation of food colouring components with different solvents

Intended class time30-45 minutes

DfE Apparatus and Techniques coveredThe codes used below match the OCR Practical Activity Learner Record Sheet (Chemistry / Combined Science) and Trackers (Chemistry / Combined Science) available online. There is no requirement to use these resources.

By doing this experiment, learners have an opportunity to develop the following skills:

4 [9]: Safe use of a range of equipment to purify and/or separate chemical mixtures including: iv) chromatography

6 [11]: Safe use and careful handling of gases, liquids and solids, including: i) careful mixing of reagents under controlled conditions

Links to Specifications:

Gateway Science (Suite A) – including Working Scientifically (WS)C2.1g describe the techniques of paper and thin layer chromatography

C2.1h recall that chromatography involves a stationary and a mobile phase and that separation depends on the distribution between phases [to include: identification of the mobile and stationary phase]

C2.1i interpret chromatograms, including measuring Rf values [to include: the recall and the use of the formula]

C2.1j suggest suitable purification techniques given information about the substances involved

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C2.1k suggest chromatographic methods for distinguishing pure from impure substances [to include paper, thin layer (TLC) and gas chromatography]

WS1.2e evaluate methods and suggest possible improvements and further investigations

WS1.3a presenting observations and other data using appropriate methods

WS1.3b translating data from one form to another

WS1.3c carrying out and representing mathematical and statistical analysis

WS1.3e interpreting observations and other data

WS1.3f presenting reasoned explanations relating data to hypotheses

WS1.3g evaluating data in terms of accuracy, precision, repeatability and reproducibility

WS1.3h identifying potential sources of random and systematic error

WS1.4a use scientific vocabulary, terminology and definitions

WS2a carry out experiments

WS2b make and record observations and measurements using a range of apparatus and methods

WS2c presenting observations using appropriate methods to include descriptive, tabular diagrammatic and graphically

WS2d communicating the scientific rationale for investigations, methods used, findings and reasoned conclusions

Twenty First Century Science (Suite B) – including Ideas about Science (IaS)C5.1.4 recall that chromatography involves a stationary and a mobile phase and that separation depends on the distribution between the phases

C5.1.5 interpret chromatograms, including calculating Rf values

C5.1.6 suggest chromatographic methods for distinguishing pure from impure substances [including the use of a) paper chromatography, b) aqueous and non-aqueous solvents, c) locating agents]

C5.1.8 suggest suitable purification techniques given information about the substances involved

IaS1.8 use appropriate scientific vocabulary, terminology and definitions to communicate the rationale for an investigation and the methods used using diagrammatic, graphical, numerical and symbolic forms

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IaS2.1 present observations and other data using appropriate formats

IaS2.4 be able to translate data from one form to another

IaS2.8 when analysing data identify patterns/trends, use statistics (range and mean) and obtain values from a line on a graph (including gradient, interpolation and extrapolation),

IaS2.9 in a given context evaluate data in terms of accuracy, precision, repeatability and reproducibility, identify potential sources of random and systematic error, and discuss the decision to discard or retain an outlier

IaS2.10 evaluate an experimental strategy, suggest improvements and explain why they would increase the quality (accuracy, precision, repeatability and reproducibility) of the data collected, and suggest further investigations

IaS2.11 in a given context interpret observations and other data (presented in diagrammatic, graphical, symbolic or numerical form) to make inferences and to draw reasoned conclusions, using appropriate scientific vocabulary and terminology to communicate the scientific rationale for findings and conclusions

Mathematical Skills coveredNo specific mathematical skills are covered in this activity.

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Technical Requirements – PER GROUP

Chemicals

Identity

Approximate quantity

required or produced

PER GROUP

Hazard information Risk information

food colouring

< 1 cm3 Not currently classified as hazardous

Concentrated pastes can temporarily stain the skin

isopropanol solvent

c. 10 cm3 WARNING: Flammable, irritant (skin, eye)

Ensure there are no naked flames present – handle solvents with care and dispose of responsibly.

surgical spirit (ethanol)

c. 10 cm3DANGER: Highly flammable. Harmful if swallowed. Irritant (eye). May cause damage to organs

acetone based nail varnish remover

c. 10 cm3DANGER: Highly flammable. Irritant (eye). May cause drowsiness or dizziness.

Equipment three food colourings solutions/gels [look for products that contain some of the same

colouring agents – e.g. E133 – brilliant blue, E110 sunset yellow, E102 tartrazine – e.g. Colour Splash Concentrated food colouring] – avoid powder colourings

three small containers, e.g. egg cups coffee filters – preferably white small drinking glass large measuring spoon fine tipped paint brush pencil ruler bull-dog clip

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NotesMost homes contain common solvents in a variety of forms. For example, isopropyl alcohol (isopropanol) can be found in rubbing alcohol or electronics cleaning solvent (e.g. Maplin RE79L), or cleaning liquids in nail varnish kits. Ethanol is the major component of surgical spirit, used for cleaning and disinfecting skin. Acetone is the major component of some nail varnish removers (check the label carefully).

Health and SafetyAvoid using powdered food colourings.

If selecting other solvents, ensure they are properly risk assessed by a competent person.

Many non-aqueous solvents are highly flammable – ensure there are no naked flames or other sources of ignition present when carrying out this activity.

Wear eye protection during practical work.

Ensure any kitchen apparatus used in the experiment is thoroughly cleaned after use

Method This method makes use of apparatus and reagents likely to be available in the home / alternative provision establishments. Despite this, the separation of mixtures by chromatography can be readily demonstrated, and provides a useful stepping stone to higher quality chromatography and measurement of Rf values.

Learner should be aware of the equipment that would be used in a standard laboratory chromatography practical – see questions.

Images from trials

Figure 1: Images from the trial

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Analysis of results – trial resultsYou can draw your own table, or use the one below:

Figure 2: Chromatograms of ‘Colour Splash – Concentrated food colouring – Sunflower, Peacock and Dark brown’ in i) tap water, ii) surgical spirit, iii) rubbing alcohol, iv) nail varnish remover

1. Describe qualitatively the difference using different solvents had on the separation

Answers will depend on the food colourings used.

In water, all food colours produced smeared chromatograms. There was some separation of a yellow and orange colouring in Sunflower. In Dark brown, the purple colour did not move significantly, while the yellow moved to the solvent front.

In surgical spirit, there was very little separation from any of the food colouring, with large smears produced for each colour.

In rubbing alcohol, yellow and orange colour moved about the same distance, with the yellow moving slightly further. There was some separation in Dark brown between the yellow/orange and purple. There was much less smearing compared with water and surgical spirit.

In acetone there was not real separation of the coloured components.

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Extension opportunities1. Describe which equipment you would use to carry out this practical in a standard

chemistry laboratory.

In place of a glass, a beaker could be used.In place of the coffee filter, a (Whatman No. 1) filter paper could be used.In place of the egg cuts, a multi-well plate could be used.In place of the paint-brush a fine tipped capillary tube could be used.

2. Explain why using your chromatograms would make calculation of accurate Rf values difficult.

The spot on the chromatogram are in general very smeared, so it would not be possible to accurately identify the spot centre.There is also significant overlap of the spots in some of the chromatograms.

3. Describe how you could use a different chromatographic technique to produce improved chromatograms.

In general, chromatograms from thin layer chromatography have better resolved spots (less smearing).

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Document updates

v1.1 February 2017 Published on qualification page

v1.2 June 2017 Updated hazard and risk information

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Chemistry PAG 3: Separation techniques

Combined Science PAG C3: Separation techniques

Suggested Activity 3: Kitchen chromatography

Learner ActivityIntroductionIn this activity you will refresh your knowledge of chromatography which you are likely to have studied in Key Stage 3 and prior.

You will separate a range of food colouring dyes by paper chromatography, making use of solvents usually available in the home. By varying the proportion of water to organic solvent, you can observe different separation of the coloured components of the food colouring.

AimsTo separate the coloured components of food colouring using commonly available solvents.

Intended class time30 minutes

Chemicals and equipment (per group) food colourings solutions/gels [look for products that contain some of the same colouring

agents – e.g. E133 – brilliant blue, E110 sunset yellow, E102 tartrazine – e.g. Colour Splash Concentrated food colouring] – see note below

household care / cleaning solvents, e.g. surgical spirit, rubbing alcohol, nail varnish remover (DANGER: flammable, harmful, irritant) – see note below

non-plastic containers, e.g. ceramic egg-cups coffee filters – preferably white small drinking glass large measuring spoon fine tipped paint brush pencil ruler bull-dog clip

Health and Safety Avoid using powdered food colourings.

If selecting other solvents, ensure they are properly risk assessed by a competent person.

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Many non-aqueous solvents are highly flammable – ensure there are no naked flames or other sources of ignition present when carrying out this activity.

Wear eye protection

Ensure any kitchen apparatus used in the experiment is thoroughly cleaned after use.

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MethodSTAGE 1: Setting up the chromatogram

1. Cut enough chromatogram papers from the coffee filter for each of the solvents you are using (plus one for water) - about 5 cm wide and about as tall as your glass

2. Draw pencil lines about 2 cm from one end of your pieces of paper

3. Mix a small amount of the food colouring in about the same volume of water in a small container (e.g. egg cup)

4. Using a fine paint brush, paint small spots of the food colouring mixture onto the pencil lines and gently blow to dry the spots. Repeat once more.

5. Repeat Steps 3 and 4 with the remaining food colourings.

STAGE 2: Running the chromatogram

6. Add about 1 cm of water into the glass

7. Using the bulldog clip, attach the top of your paper to the pencil, and lower the paper into the flask – ENSURE the top of the water is BELOW the pencil base line.

8. Allow the water to soak up the paper until about 1 cm from the pencil.

9. Remove the paper from the glass, and mark the highest point of the solvent with a pencil line.

10. Place the chromatogram on a piece of absorbent towel until dry.

11. Repeat stage 2 with the remaining solvents.

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Figure 1: Experimental set-up for running the paper chromatography

Analysis of resultsTake a picture of the three chromatograms you ran and stick them in below:

Your ability to analyse your observations may depend on how much of the GCSE Chemistry/Combined Science course you have studied. Your teacher will let you know which questions you should focus on:

1. Describe qualitatively the difference using different solvents had on the separation

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Extension opportunities1. Describe which equipment you would use to carry out this practical in a standard

chemistry laboratory.

2. Explain why using your chromatograms would make calculation of accurate Rf values difficult.

3. Describe how you could use a different chromatographic technique to produce improved chromatograms.

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DfE Apparatus and Techniques coveredIf you are using the OCR Practical Activity Learner Record Sheet (Chemistry / Combined Science) you may be able to tick off the following skills:

Chemistry Combined Science4-iv 6-i 9-iv 11-i

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