How to develop students’ observation skills in practical chemistry

Derek Denby looks at how to develop students’ observation skills in practical chemistry

Why are observations important in chemistry?

Penicillin culture, helium balloons, radioactive symbol and sticky notes

Source: catolla / chainatp / hanohiki / gerenme / iStock / Getty Images Plus

Figure 1: Penicillin culture, helium balloons, radioactive symbol and sticky notes

Look at the images in figure 1. What is the connection between them?

The link is that these are all examples of careful observations in the laboratory that have had far reaching effects on everyday life.

Alexander Fleming’s observation of a culture plate led to the development of antibiotics. The investigation of a glue by Spencer Silver and Arthur Fry introduced us all to sticky notes. The observation of an unexplained line in a solar spectrum during an eclipse identified helium as a new element. Images on Henri Becquerel’s photographic plates led Marie Curie to coin a new word – radioactivity. Each of these observations has had profound consequences.

Examples like these provide an effective way of engaging student interest and reminding them of the importance of their own observations in following and understanding chemical change.

Developing practical skills and progression

Making and recording observations is a key feature of skill development from key stage 1 (KS1) to key stage 4 (KS4).

National curriculum requirements
Key stage 1Key stage 2Key stage 3Key stage 4

Observe closely using simple equipment

Make systematic and careful observations

Make and record observations and measurements using a range of different methods and suggest possible improvements

Make and record appropriate observations during chemical reactions

Use observations and ideas to suggest answers to questions

Use straightforward scientific evidence to answer questions or to support findings

   

There is a danger that because careful observation has been emphasised since KS1, we take it for granted in later years and insufficiently challenge observations that are ambiguous, inappropriate or unclear.

What do we really mean by observation? How can observations help students better understand chemical change?

Sometimes students ‘can’t see the wood for the trees’ as they pick out individual observations but fail to link them together to make sense of the overall change. Encourage students to think of each observation as a piece in a jigsaw puzzle they can put together to make up the complete picture.

Consider, for example, adding a small piece of calcium to a beaker containing cold water and a few drops of universal indicator. How do the following observations help students explain the reaction involved?

  • Bubbles rise from the calcium at the bottom of the beaker
  • The solution becomes blue
  • A white precipitate is gradually formed
  • The beaker becomes warm

Reaction of zinc and copper sulfate

Source: Alexandre Dotta / Science Photo Library

The reaction of zinc and copper(II) sulfate solution

Observations are just the starting point. We interpret what we see in terms of particles such as atoms and molecules and often write equations to describe the changes. Many students find moving back and forward between the macro, symbolic and sub-microscopic levels very challenging.

Teacher questions are a powerful tool to help students make the shift in their thinking between levels. As students’ progress from KS1 to KS4, the concepts they study become increasingly more complex. The links between observations and concepts need to be continually updated and refined and the increasing sophistication of the theory should be matched by an increasing sophistication of the questions teachers ask.

Think about the questions you might ask when students add excess zinc to copper(II) sulfate solution (table 1).

Table 1: Questions to encourage observation and inference in the reaction of zinc and copper (II) sulfate solution
KS3: Questions to encourage observation What changes do you notice about the solid in the beaker?
What changes do you notice about the solution?
Is there a change in temperature of the reaction mixture?
KS3: Questions to encourage inference What is the brown solid produced in the reaction?
What type of reaction is this?
Which metal is more reactive, copper or zinc?
KS4: Questions to encourage observation What information does touching the beaker provide you?
How can you tell the zinc is in excess?
How can you tell when the reaction is finished?
KS4: Questions to encourage inference What particles are responsible for the blue solution?
What is meant by a spectator ion?
What has happened to the zinc atoms?

Coloured and colourless solutions

Source: GIPhotoStock / Science Photo Library

For some students, language may be a barrier. Over time, students need to become familiar with scientific ways of communicating what they see and be able to use specialist chemical vocabulary accurately.

They need to appreciate that the terms clear and colourless have different meanings and to be able to use words like precipitate, residue, solution, suspension, effervescence and distillate in appropriate ways. They need to realise that an observation such as ‘it went yellow’ is ambiguous, unclear and unscientific. Card activities in which students match words with their meanings are a useful way of exploring student misconceptions and misunderstandings, particularly if alternative definitions are included as distracters.

Practical problems and suggested solutions

Microscale is a great way of developing students’ observational skills. The very nature of using reduced scale apparatus and small quantities of materials means that students have to look very carefully at what is happening. Details of microscale experiments can be found in a range of resources including the Royal Society of Chemistry publications Microscale chemistry1 and Inspirational chemistry.2 CLEAPSS have also developed a wide range of novel microscale experiments suitable for use in KS3 and KS43 and the SSERC website4 provides a wealth of detail. Some awarding organisations suggest a series of microscale experiments as alternatives to traditional experiments at KS4.

Microscale is a great way of developing students’ observational skills. The very nature of using reduced scale apparatus and small quantities of materials means that students have to look very carefully at what is happening. Details of microscale experiments can be found in a range of resources including the Royal Society of Chemistry publications Microscale chemistry and Inspirational chemistry. CLEAPSS have also developed a wide range of novel microscale experiments suitable for use in KS3 and KS4 and the SSERC website provides a wealth of detail. Some awarding organisations suggest a series of microscale experiments as alternatives to traditional experiments at KS4.

Adding drops of solutions to each other on a laminated sheet is a very quick, clean, economical and effective way of enabling students to observe reactions that result in colour changes or the formation of a precipitate. They provide a good alternative to traditional test tube experiments. This drop-scale approach can even be used quantitatively to determine the concentration of copper in brass.5 Displacement reactions between small pieces of metal and other metal ions can also be viewed in this way. The formation of metallic iron in such reactions can be shown quite dramatically by passing a small magnet over the pool of reaction mixture.6

Drop-scale chemistry

Source: Kay Stephenson

Adding drops of solutions to each other on a laminated sheet is a very quick, clean, economical and effective way of enabling students to observe reactions that result in colour changes or the formation of a precipitate

Adding drops of solutions to each other on a laminated sheet is a very quick, clean, economical and effective way of enabling students to observe reactions that result in colour changes or the formation of a precipitate. They provide a good alternative to traditional test tube experiments. This drop-scale approach can even be used quantitatively to determine the concentration of copper in brass. Displacement reactions between small pieces of metal and other metal ions can also be viewed in this way. The formation of metallic iron in such reactions can be shown quite dramatically by passing a small magnet over the pool of reaction mixture.

Petri dishes can be used to overcome the problem of observing the properties of a toxic gas such as chlorine or sulfur dioxide. Reagents that will generate small amounts of the gas are placed in a blister pack in the centre of the dish with appropriate reagents or test papers placed round the outside. The lid is placed on the dish to prevent escape of the gas. Petri dishes can also be used as effective electrolysis cells.7

Petri dishes can be used to overcome the problem of observing the properties of a toxic gas such as chlorine or sulfur dioxide. Reagents that will generate small amounts of the gas are placed in a blister pack in the centre of the dish with appropriate reagents or test papers placed round the outside. The lid is placed on the dish to prevent escape of the gas. Petri dishes can also be used as effective electrolysis cells.

Variety of approach is always helpful when developing student practical skills. Instead of microscale, from time to time you might use a visualiser or low-cost digital microscope so the whole class can see the same experiment at the same time on a screen or whiteboard. You could focus on the formation of a precipitate in a Petri dish or on the thermometer bulb during fractional distillation. How about projecting a microscope image of a disappearing cross rate experiment so that everyone can do the timing?

Allowing students to take their own photographs or videos of experiments, perhaps using a smartphone, is also an effective way of training them to select key observations.

Useful resources
Resource Comment

Developing and using models: linking concepts and evidence (rsc.li/3xYG86)

This resource looks at ways of helping students move between macro and sub-microscopic levels

The chemical history of a candle – updated version (youtu.be/gf8ESM4BlfQ)

The chemical history of a candle was the title of six lectures given by Michael Faraday at the Royal Institution in 1848. He began his lectures by asking his audience to record as many observations as possible about a burning candle. These lectures were the inspiration behind the 2005 lecture by Ian Russell.

The nature of science: black box (rsc.li/1yL1L1x)

This group of activities help KS3 students appreciate the difference between observation and inference

Considering colour vision deficiency

Colour visual deficiency (CVD) or colour blindness affects about 4.5% of the population – mainly, but not entirely, male. By year 7 approximately 80% of children have never been screened for CVD so they may be unaware of their condition.

Colour visual deficiency (CVD) or colour blindness affects about 4.5% of the population – mainly, but not entirely, male. By year 7 approximately 80% of children have never been screened for CVD so they may be unaware of their condition.8

Coloured solutions as seen by normal vision (above) and by a student with a form of colour vision deficiency (below)

Source: Andrew Lambert Photograph / Science Photo Library / Colour Blind Awareness

Coloured solutions as seen by normal vision (above) and by a student with a form of colour vision deficiency (below)

Some specific problems that students with CVD may experience in chemistry are difficulty in:

  • Reading universal indicator paper accurately
  • Identifying the end point in an acid–base titration
  • Identifying metal ions using a flame test
  • Describing the colours of solutions and precipitates

This raises some important questions for teachers. Do you know if any of your students have colour vision deficiency? Do you try to help them by asking them to work in pairs for some experiments so that a partner can help describe colours, or by providing alternative acid–base indicators that they can see more easily? If you have CVD, have you considered how this might impact on your teaching?

Derek Denby is an independent science education consultant based in the UK