Geology PAG 3: Investigating crystalline processes

Suggested Activity 1: Crystallisation of salolInstructions for teachers and techniciansThis practical activity is composed of two parts; a teacher/technician section and the student activity which can be found on page 7. This practical activity supports OCR AS/A Level Geology.

When distributing the activity section to the students 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 OCR AS and A Level Geology specifications helping to fulfil the requirements of the Practical Endorsement.

These are not required activities, nor are they coursework tasks.

You may modify these activities to suit your students and centre. Alternative activities are available from, for example, ESTA, Earth Learning Idea, CLEAPSS and publishing companies.

Support for mapping activities to the requirements of the Practical Endorsement is available from OCR – see www.ocr.org.uk/positiveaboutpractical or email us at PASS@ocr.org.uk.

Students can collaborate during the activities but each student must individually demonstrate competence in each of the practical skills being assessed (see Practical Skills below).

It is possible for a student to achieve some but not all of the practical skills involved in an activity (and this can be recorded as individual skills in the OCR PAG Tracker).

Further details are available in the specifications (Practical Skills Topics).

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 students. 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 student.

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IntroductionStudents will investigate the effect of ambient temperature and cooling rate on the formation of crystals from a melt. Salol (phenyl salicylate, C13H10O3) is a solid at room temperature but has a melting point of 42 ±2°C, and so can be used to model the crystallisation of igneous rocks from a melt in the classroom. The growth of crystals in the melt modifies the physical properties of the melt and by using simple equipment students can study the effect of crystallisation on the viscosity of the melt. Learners are expected to be familiar with igneous textures.

Aims to determine the relationship between cooling rate, ambient temperature and crystal size to use these observations to describe the behaviour of salol as an analogy to igneous rock to safely and carefully handle a range of equipment and hot liquids to record data appropriately and evaluate sources of error and modify procedures

Intended class time 1 hour

Practical Skills – competence assessed by the teacher1.2.1 (b) safely and correctly use a range of practical equipment and materials1.2.1 (c) Follow written instructions 1.2.1 (d) make and record observations/measurements 1.2.1 (f) present information and data in a scientific way1.2.1 (j) use a wide range of experimental and practical instruments, equipment and techniques appropriate to the knowledge and understanding included in the specification1.2.2 (g) production of annotated scientific drawings of fossils, or small scale features, from hand samples using a light microscope, or hand lens observation1.2.2 (j) use of appropriate apparatus to record a range of quantitative measurements (to include mass, time, volume, temperature and length)1.2.2 (l) use of methods to increase accuracy of measurements

CPAC – competence assessed by the teacher(1) follows written procedures(2) applies investigative approaches and methods when using instruments and equipment(3) safely uses a range of practical equipment and materials(4) makes and records observations.

Links to Specifications2.1.1 (a) minerals as naturally occurring elements and inorganic compounds whose composition can be expressed as a chemical formula2.1.1 (b) rock-forming silicate minerals as crystalline materials built up from silicon–oxygen tetrahedra to form frameworks, sheets or chains and which may have a range of compositions2.1.1 (c)(iv) the techniques and procedures used to measure mass, length and volume2.1.2 (b)(i) igneous textures, crystal shape and crystal size as evidence for depth of formation and rate of cooling of igneous rocks2.1.2 (b)(ii) (ii) the diagnostic properties of igneous textures and crystal shape in samples, photographs and thin section diagrams

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2.1.2 (b)(iii) the representation using drawings and annotated diagrams of igneous textures and crystal shape in samples2.1.2 (b)(iv) the techniques and procedures used to measure temperature

Mathematical Skills – learning opportunity within activity Mathematical skills must be applied in the recording of the data and calculations, and in

analysing the data. These steps require the appropriate application of the following mathematical skills:o M1.1 Recognise and make use of appropriate units in calculations.o M1.3 Use an appropriate number of significant figures.o M1.6 Estimate results.o M2.5 Understand the principles of sampling as applied to scientific data.o M2.9 Plot two variables from experimental or other linear data.

Chemicals

Label Identity Hazard information

Phenyl salicylate, salol White solid

WARNINGCauses serious eye irritation and skin irritation. May cause respiratory irritation.Some suppliers also label this as Toxic to aquatic life with long lasting effects

EquipmentEach student will require: salol (phenyl salicylate, C13H10O3), spatula boiling tube 2 × microscope slides, (6 × slides will allow for repeats at each temperature) microscope – hand lens may be used if no microscopes available 2 × beakers – 400 cm3 or 250 cm3

thermometer graduated in divisions of 0.5°C and a range of at least −10°C to +50°C source of ice cubes and hot water (~50°C), for example a kettle or flask pipette paper towel stop watch ruler

Health and Safety Health and safety should always be considered by a centre before undertaking any

practical work. A full risk assessment of any activity should be undertaken including checking the CLEAPSS website (http://www.cleapss.org.uk).

Salol (phenyl salicylate) is covered under CLEAPSS Hazcard number 52. Students should wear eye protection when working with salol

Hot water may cause burns or scalding Glassware poses a risk of cuts if not handled carefully.

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NotesCentres are advised to trial this activity before using it with students. In particular: Salol may have a relatively short shelf life and it is advisable for it to be prepared as

required for the practical. It can be created by heating salicylic acid with phenol if not ready made. Each group will require approximately 5 cm3.

The cooling experiment is a short activity; however students are expected to make repeat observations, the cooling of the warm microscope slides may take longer.

Student records of the practical could be supplemented with photographs, it is possible to take photographs using smartphones looking down a microscope lens, or a ×30 clip-over smartphone microscope.

The communal hot water supply need be no more than 50°C and could be a water bath, kettle or tap (if this is warm enough). Higher temperatures are beyond the range of the most common 0.5°C thermometers, increase the risk of accidents and reduces the predictability of the experiment as when heated much beyond its melting point (42 ±2°C) salol is susceptible to displaying supercooling which will delay crystallisation.

Answers and Guidance to Extension Activities7. Changes to the volume of the reservoir of the thermometer (normally caused by

overheating) or oxidation of the alcohol can move thermometers out of calibration. By using the icebath (triple point of water at 100 kPa is a fixed point of 0.01°C) a calibration correction can be found.

8. Expect smaller crystals at lower temperatures, large crystals at higher temperatures. At intermediate temperatures you would expect crystal sizes in between those recorded at the data points. At very low temperatures you may expect glassy textures.

9. Smaller crystals form within extrusive rocks associated with MORs, hot-spot volcanoes, or lava from convergent margin volcanoes or from the chilled margins of small scale intrusions (sills or dykes). This is due to the rate of cooling being fast (minutes to hours), which does not allow time for the crystals to grow larger. Heat energy transfer from the lava and magma is fast due to the difference in temperature. Larger crystals form in intrusive rocks associated with rising batholiths at convergent margins, cooled magma chambers or plutonic rocks. This is due to the rate of cooling being very slow (millions of years), which allows time for the crystals to grow larger. Heat energy transfer from the

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magma is slow due to the smaller difference in temperature (geothermal gradient) and the insulating effect of the surrounding country rock.

RecordsAs evidence for the Practical Endorsement, students: should not need to re-draft their work, but rather keep all of their notes as a continuing

record of their practical work, dating their work clearly, should record any measurements taken to the number of significant figures (resolution)

appropriate. This should be recorded clearly in a table format with appropriate units, should record any modifications to supplied procedures, including their own risk

assessments and methods where appropriate.

Extension questions help students develop their understanding of the underlying geological theory and are a preparation for the written examinations. They also help students to develop the practical science skills assessed indirectly in the written examinations and they should be encouraged to record their data appropriately, for example showing full workings in calculations, and stating final answers to the appropriate number of significant figures.

Document updatesv1.0 September 2017 Original version.

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Example of salol crystals formed on a cold microscope slide. Photo taken using a ×30 clip-over smartphone microscope, with standard mm division ruler for scale.

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OCR Resources: the small printThis formative assessment resource has been produced as part of our free A Level teaching and learning support package. All the A Level teaching and learning resources, including delivery guides, topic exploration packs, lesson elements and more are available on the qualification webpages.

If you are looking for examination practice materials, you can find Sample Assessment Materials (SAMs) on the qualification webpages: http://www.ocr.org.uk/qualifications/as-a-level-gce-geology-h014-h414-from-2017/ OCR’s resources are provided to support the teaching of OCR qualifications, but in no way constitute an endorsed teaching method that is required by the Board, and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these resources.

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Geology PAG 3: Investigating crystalline processes

Suggested Activity 3: Crystallisation of salol

Student activityIntroductionIn this practical activity you will investigate the effect of ambient temperature and cooling rate on the formation of crystals from a melt. Salol (phenyl salicylate, C13H10O3) is a solid at room temperature but has a melting point of 42 ±2°C, and so can be used to model the crystallisation of igneous rocks from a melt in the classroom. The growth of crystals in the melt modifies the physical properties of the melt and by using simple equipment you can study the effect of crystallisation on the viscosity of the melt.

Aims to determine the relationship between cooling rate, ambient temperature and crystal sizeto use these observations to describe the behaviour of salol as an analogy to igneous rockto safely and carefully handle a range of equipment and hot liquidsto record data appropriately and evaluate sources of error and modify procedures

Intended class time1 hour

Chemicals Label Identity Hazard information

Phenyl salicylate, salol White solid

WARNINGCauses serious eye irritation and skin irritation. May cause respiratory irritation.Some suppliers also label this as Toxic to aquatic life with long lasting effects

Equipmentsalolboiling tubemicroscope slidesmicroscope2 × beakersthermometer

source of hot water (~50°C)pipettepaper towelstop watchruler

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Health and Safety Salol (phenyl salicylate) is covered under CLEAPSS Hazcard number 52. Eye protection should

be worn when working with salol. Handle glassware with care.

ProcedureBefore starting your practical work, read the information below. Decide how you will organise your practical work, and which observations you need to make and/or which measurements you need to take. Ensure that you record all of your results in a suitable format.

1. Fill one of your beakers with hot water. Place a small amount of salol (approximately 1g) into a boiling tube, then place the boiling tube into the beaker.

2. Fill the second beaker with hot water. Place two microscope slides into the beaker and allow the temperature of the slides to equilibrate with the water. Record the water temperature in both beakers.

3. Remove the microscope slides from the beaker and dry them with the paper towel, making sure that they are completely dry.

4. Using a pipette, take the melted salol and add one drop to one of the microscope slides using the pipette. Place the second slide of the same temperature on top.

5. Observe the slides through the microscope and record how long it takes for the first crystal to form, the time for the salol to completely crystallise and the size of the crystals.

6. Repeat the procedure for steps 2 to 5 for an intermediate temperature (between ‘hot’ and ‘room temperature’), room temperature and for an ice bath (beaker filled with ice cubes and cold water). You may need to modify the procedure.

7. Finally place the thermometer in the ice bath, allow it to equilibrate and record the temperature displayed on the thermometer. If the reading is not 0°C, calculate the calibration correction and apply to all your temperature readings.

Extension opportunities8. Describe what you observed as the salol cooled; include diagrams of what you saw.9. (a) Calculate the rate of cooling at each temperature (i.e. 1 / time between first formation and

complete crystallisation).(b) Plot your results as a scattergraph/scatter-plot with temperature as the independent

variable, and determine the line of best fit.(c) Based on your experience how would you modify the experimental procedure you used to

improve the accuracy of your results?

RecordsAs evidence for the Practical Endorsement, you need records in your field notebook of: the data collected from their individual readings in a clear and logical format, with all

measurements taken to the number of decimal places (resolution) appropriate for the apparatus used. These should be recorded clearly in a table format, with appropriate units,

any modifications to supplied procedures, including your own risk assessments and methods where appropriate.

All work should be clearly dated.

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In addition you should have considered the above questions as the answers to these questions will aid you in preparation for your written examinations.

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