Chemistry PAG 4: Distillation

Combined Science PAG C2: Distillation

Suggested Activity 2: Fractional distillation of a crude oil substitute

Instructions and answers for teachers and techniciansThese 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 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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IntroductionFractional distillation is a key separation technique for crude oil. Carrying out this activity provides practical experience to help consolidate theoretical links between structure and properties of substances.

Genuine crude oil cannot be used in schools as it contains benzene and other carcinogenic substances. The crude oil substitute suggested shows good separation into fractions.

This activity is based on the method described in Section 13 (Mainly Chemistry) of the CLEAPSS Laboratory Handbook: www.cleapss.org.uk/attachments/article/0/Sec13.pdf.

An alternative activity is available from the Royal Society of Chemistry/Nuffield Foundation Practical Project: http://www.rsc.org/learn-chemistry/resource/res00000754/the-fractional-distillation-of-crude-oil.

A useful video of this type of activity is available: https://www.youtube.com/watch?v=uWOI-mXDWtk

A subsequent demonstration using a fractional distillation column is suggested to help learners make the conceptual links required to understand how the fractional distillation column in oil refineries work. A useful video on this technique is available: https://www.youtube.com/watch?v=0x2-8dedmE4

A range of resources related to crude oil refinery are available: http://www.rsc.org/learn-chemistry/resource/res00000027/oil-refining

AimsTo separate a crude oil substitute, and investigate the properties of the fractions.

Intended class time30-40 minutes

DfE Apparatus and Techniques coveredThe codes used below match OCR Practical Activity Learner Record Sheet (Chemistry / Combined Science) available online.

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

1 [1]: Use of appropriate apparatus to make and record a range of measurements accurately, including: ii [iv]) time

2 [2] Safe use of appropriate heating devices and techniques including use of (i) a Bunsen burner

3 [8]: Use of appropriate apparatus and techniques for: i) conducting and monitoring chemical reactions

4 [9] Safe use of a range of equipment to purify and/or separate chemical mixtures including (v) distillationVersion 1.1 – March 2017 2 © OCR 2017

6 [11] Safe and careful handling of gases, liquids and solids, including ii) using appropriate apparatus to explore chemical changes and/or products

Links to Specifications:

Gateway Science (Suite A) – including Working Scientifically (WS)C2.1f describe, explain and exemplify the processes of filtration, crystallisation, simple distillation, and fractional distillation

C2.3d use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur

C6.2a recognise functional groups and identify members of the same homologous series

C6.2j describe the separation of crude oil by fractional distillation [to include: the names of the fractions]

C6.2k explain the separation of crude oil by fractional distillation [to include: molecular size and intermolecular forces]

C6.2l describe the fractions as largely a mixture of compounds of formula CnH2n+2 which are members of the alkane homologous series

WS1.2c apply a knowledge of a range of techniques, instruments, apparatus and materials to select those appropriate to the experiment

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

WS1.3e interpreting observations and other data

WS1.3f presenting reasoned explanations relating data to hypotheses

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

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Twenty First Century Science (Suite B) – including Ideas about Science (IaS)C3.4.3 Describe and explain the separation of crude oil by fractional distillation

C3.4.4 describe the fractions as largely a mixture of compounds of formula CnH2n+2 which are members of the alkane homologous series

C3.4.5 use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur

C3.4.4 describe the fractions of crude oil as largely a mixture of compounds of formula CnH2n+2 which are members of the alkane homologous series.

C5.1.7 describe, explain and exemplify the processes of filtration, crystallisation, simple distillation, and fractional distillation

IaS2.1. present observations and other data using appropriate formats

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),

IaS2.11. 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 defined mathematical skill is covered in this experiment.

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Technical Requirements – PER GROUP

Chemicals

Identity

Approximate quantity

required or produced

PER GROUP

Hazard information Risk information

crude oil substitute and PRODUCED fractions

see Notes for recipe

c. 8 cm3

DANGER: May be fatal if swallowed and enters airways. May cause drowsiness or dizziness. Highly flammable liquid and vapour. Causes skin irritation. Repeated exposure may cause skin dryness or cracking. Very toxic to aquatic life with long lasting effects. Suspected of damaging fertility. May cause damage to organs through prolonged or repeated exposure.

See Hazcard 45A. Stopper fractions once collected. Ensure the room is well ventilated. Ensure mineral wool is used in the heated boiling tube.

Equipment eye protection mineral wool (c. 5 cm3) side–arm boiling tube bung with hole for thermometer thermometer (up to c. 300C) – glass OR digital test tubes (3) test tube bungs (3) watch–glass c. 10 cm (3) * glass marker pen stand, boss and clamp heat proof mat Bunsen burner splints timer paper towels

* If lighting the fractions on the watch-glasses, ensure they are hardened glass (borosilicate). Otherwise crown bottle tops (e.g. from beer bottles) that have had the inner plastic burnt out can be used for the flammability test.

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NotesFollow CLEAPSS Recipe 32 for crude-oil substitute: http://www.cleapss.org.uk/attachments/article/0/RBPrint.pdf

55% liquid paraffin, 20% paraffin oil, 11% white spirit, 5% petroleum ether 100-120, 4% petroleum spirit 80-100, 6% petroleum ether 60-80 – all v/v. Other recipes can be used depending on availability of reagents, and these should be risk assessed in the usual way.

Addition of artist’s Ivory Black Oil paint makes the crude-oil substitute appear more like genuine crude oil. Your school’s art department may have supplies of this in stock.

Mineral wool is used to absorb the liquid and to provide a surface for smooth distillation.

If possible, the equipment should be dismantled as soon as it has cooled after the distillation. However, due to difficulty in cleaning apparatus, it would be advisable to dedicate the apparatus to the experiment.

If side–arm boiling tubes are not available, an alternative is to use a two hole bung and normal boiling tube, inserting both the thermometer and delivery tube through the bung.

Ensure the watch–glasses are Pyrex/borosilicate glass.

Health and SafetyEye protection should be worn at all times.

Fractions are flammable, and should be bunged immediately.

Learners should observe the apparatus carefully during heating and stop heating if any smoke/vapours are observed escaping from the top of the side-arm tube.

Method Collect fractions in small test tubes at approximately 50°C intervals up to about 200°C.

Test the fractions for odour, viscosity and ease of combustion.

The fraction up to 250C can also be collected, although strong sustained heating is required.

An extension to the method is to have the learners compare the height of the fractions collected to a test tube containing 1 cm3 of water. This can then lead on to discussion about the proportions of different fractions in crude oil and the need for cracking.

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Images from trials

Experimental setup

The fractions produced Testing the viscosity of the fractions

Testing the flammability of the fractions

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

Fraction property

Fraction Boiling range / C Odour Time to flow down watch glass / s

Ease of combustion

A 40 – 100 white spirits < 1 easy

B 120 – 160 floor polish c. 2hard – splint flame increased in size

C 180 – 200 diesel c. 6 doesn’t light

1. Describe and explain the trends in the properties of the fractions as the boiling point increases. [6 marks]

As the boiling range increases the smell of the fraction becomes less strong time to flow down the watch glass increases OR viscosity increases ease of combustion decreases

As the boiling range increases the substance becomes less volatile so fewer molecules reach the nose molecules are longer, so there are stronger intermolecular forces between

the molecules substance becomes less volatile so mixes less well with air making

combustion harder

Extension opportunities1. Alkanes are a homologous series. Explain this phrase, and state and explain the

general formula for alkanes. [3 marks]

A homologous series is a family of compounds with the same general formula that vary by a CH2 unit The general formula of alkanes is C2H2n+2 , which means for every carbon atom in the molecule, there are twice as many plus two hydrogen atoms .

2. Write a balanced equation for the incomplete combustion of decane (C10H22), and use this to help explain why longer alkanes produce a smoky flame. [2 marks]

(allow any balanced incomplete combustion equation showing at least some C(s))e.g. C10H22(l) + 8.5O2 6C(s) + 2CO(g) + 2CO2(g) + 11H2O During incomplete combustion, soot (C(s)) is produced which is observed as the smokiness of the flame

3. In terms of how the crude oil is heated, describe and explain how laboratory and

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industrial processes differ in how crude oil is separated. [5 marks]

In laboratory based fractional distillation, the mixture is gradually heated with the fractions boiling off in order of increasing boiling range In industrial fractional distillation, the crude oil is heated in a furnace to vaporise the majority of the substances which then travel up the distillation tower that has a temperature gradient from bottom (hot) to top (cool) and the fractions condense as they move up the tower .

Document updatesv1.1 March 2017 Published on qualification page

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Chemistry PAG 4: Distillation

Combined Science PAG C2: Distillation

Suggested Activity 2: Fractional distillation of a crude oil substitute

Learner ActivityIntroductionCrude oil is a mixture of hydrocarbons, and unrefined has limited uses. By separated crude oil into groups of molecules of similar size, called fractions, various useful substances are formed such as petrol, diesel, kerosene etc. The separation can be achieved by fractional distillation, which depends on the different boiling points of the hydrocarbons, which in turn is related to the size of the molecules and the intermolecular forces between them.

AimsTo separate a crude oil substitute, and investigate the properties of the fractions.

Intended class time30-40 minutes

Chemicals and equipment (per group) eye protection mineral wool (c. 5 cm3) side–arm boiling tube bung with hole for thermometer thermometer (up to c. 300C) – glass OR digital test tubes (3) test tube bungs (3) watch–glass (c. 10 cm) (3) (bottle tops – 3 – your teacher will let you know if you are using these) glass marker pen stand, boss and clamp heat proof mat Bunsen burner splints timer paper towels crude oil substitute (DANGER: Highly flammable and harmful; c. 8 cm3)

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Health and safety Eye protection should be worn at all times. Check the boiling tube for any cracks before heating – return any damaged glassware to

your teacher. When smelling the fractions, hold the tube about 15 cm from your nose and waft your hand

over the top towards your nose. DO NOT place the tube next to your nose. Ensure the watch–glasses are on heat–proof mats before lighting the fractions. Watch carefully the top of the boiling tube – if any fumes/smoke starts to escape, stop

heating.

Method Separation of the crude oil substitute

1. Place mineral wool to a depth of about 5 cm in the bottom of the side-arm boiling tube.

2. Add about 7–8 cm3 of crude oil substitute to the mineral wool.

3. Clamp the boiling tube at about 30, place the bung and thermometer into the end of the tube, and ensure the bulb of the thermometer is at the same level as the side-arm.

4. Label three test tube A, B, C, and place the delivery tube in test tube A.

5. Holding the Bunsen burner by the base, and using a half-blue flame, GENTLY heat the side-arm boiling tube around the base and the side.

6. Collect fractions over these approximate ranges:a. room temperature – 100C (GENTLE heating is required here to ensure good

fractional distillation of this fraction)b. 100–150Cc. 150–200C (this fraction requires stronger heating).

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Figure 1: The experimental setup for small scale fractional distillation.

Analysis of the fractions

1. Test the odour of fraction: gently waft the fumes towards your nose – DO NOT smell directly from the test tube.

2. Test the viscosity of the fraction: place 2–3 drops at one end of the watch glass, tip to about 45, and time how long the drop takes to move across the watch glass.

3. Test the ease of lighting the fraction: add about 0.5 cm3 of the fraction to the watch-glass (or a prepared bottle top – you teacher will let you know which) and light the fraction with a lit splint.

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

Fraction property

Fraction Boiling range / C Odour

Time until liquid start to drip on

pouring / sEase of

combustion

A

B

C

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 and explain the trends in the properties of the fractions as the boiling point increases [6 marks]

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Extension opportunities1. Alkanes are a homologous series. Explain this phrase, and state and explain the

general formula for alkanes. [3 marks]

2. Write a balanced equation for the incomplete combustion of decane (C10H22), and use this to help explain why longer alkanes produce a smoky flame. [2 marks]

3. In terms of how the crude oil is heated, describe and explain how laboratory and industrial processes differ in how crude oil is separated. [5 marks]

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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 Science1-ii 2-i 3-i 4-v 1-iv 2-i 8-i 9-v6-ii 11-ii

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