gases – Science-Education-Research

Thank you, BBC: I'll give you 4/5

BBC corrects cruel (to cats) scientific claim on its website

Keith S. Taber

I just got 80% on a science test for primary school children

I've just scored 4/5 (80%) on an on-line KS2 science test on the BBC (the British Broadcasting Corporation) educational website. 80% sounds quite good out of context, but I am a science teacher and KS2 is meant for 7-11 year olds.

The BBC awards me 4/5 for my primary level science knowledge about the states of matter

My defence is that the question I got wrong was ambiguous (but, as Christine Keeler might have said, I would say that).

I was actually getting round to checking on something from a while back.

In 2019 I came across something on the website that I thought was very misleading – and I complained to the BBC through their website form. I had an immediate, but generic response:

"Thank you for taking the time to send us your comments. We appreciate all the feedback we receive as it plays an important role in helping to shape our decisions.
This is an automated message (sorry that we can't reply individually) to let you know that we've read your comments and will report them overnight to staff across the BBC for them to read too (after removing any personal details). This includes our programme makers, commissioning editors and senior management.
Thanks again for contacting the BBC.
BBC Audience Services.
NB: Please do not reply to this email. It includes a reference number but comes from an automated account which is not monitored."
Email: 6th Sept., 2019

This kind of response is somewhat frustating. My complaint had been recieved, and would be passed on, but it looked like I would get no specific response (as presumably if my "comments" were to be reported to relevant staff "after removing any personal details", those staff would not be in a position to let me know if they were following up, dismissing, or simply ignoring, my comments.) Indeed, I never did get any follow up.

So, my intention was to check back after a decent period had elapsed (n.b., where does all the time go?) and see if anything had been changed in response to my complaint. Strictly, if there had been a change this could be because:

a) I complained
b) someone else/some other people complained (i.e., people who's complaints were taken more seriously than mine)
c) I was one of number of people who complained
d) material had been updated compleltely independently of any compaints

That is, I could not know if I personally had had any effect, BUT if the offending material (because as a chemist I was offended professionally, even if not personally) was still there then I would know my compaint had not been heeded.

So, I intended to check back; I expected to find no change (as pointing out blatant, basic, errors in the science in the English National Curriculum to government ministers did not have any effect, so the BBC…? ); and, if so, I thought of following up with an email or an old fashioned snail-mail … ("…yours, disgusted of Cambourne"*).

Well done, BBC

So, I am happy to publicly acknowledge that the BBC has changed its materials appearing under the heading 'What are the states of matter?'

The topic comprises of a short animation (with odd anthropomorphised {"guys"} geometric shapes handling examples of the states of matter: solid, liquid and gas); a series of bullet points on each state; a sorting task; and then the set of five objective (multiple choice) questions.

There are a number of issues with the examples used here, as discussed below. But the main focus of my complaint, a cartoon cat, has now been released from the indignity of being classified as a state of matter. Yes, a cat!

Limitations of the three states of matter model

The idea that matter can exist in three states is a pretty important foundation for a good deal of other science.

However there is big problem with the generality of the model. Basically it really applies to pure samples of substances: generally substances (not materials in general, and certainly not objects) exist as solids, liquids, or gases, depending on the conditions of temperature and pressure – although at high enough temperatures plasmas are formed (and theoretically when hot enough even the atomic cores, and eventually nuclei would break down – but those conditions are pretty extreme and not found in the typical home or classroom).

Examples of substances include water, salt, calcium carbonate, iron, mercury, hydrogen, graphite, carbon dioxide, sulphur… that is, elements and compounds. Of course, many of these are seldom met in pure form in everyday life outside school science labs.

Most materials that people come across are mixtures or composites. Mixtures often exist as solutions or suspensions – as gels or foams or emulsions – not as solids, liquids or gases.

This is probably why the terms 'solids', 'liquids' and 'gases' actually have two sets of meanings – the science or technical sense, and the everyday or 'life-world' sense. So milk is a liquid_(everyday) as you can pour some into your tea cup and a block of wood is a solid_(everyday) as it retains its shape and integrity as you nail it to another structure. But milk and wood are not substances – and so not liquid_(scientific) or solid_(scientific).

Does this matter? Yes, because if we are teaching children things in science lessons, it would be good to get the science right. A solid will melt at a distinct melting temperature to give a liquid which will boil at a distinct boiling temperature. Wood, for example, does not.

Wood is a complex material. It has gas pockets. It has (variable) moisture content, and the structure contains various compounds – lignin, cellulose, and many more. The response to heating reflects that complex constitution.

The BBC's examples of solids, liquids, and gases

The BBC website suggests examples of the three states of matter to introduce primary age students to the concept.

Animation:

Solids: block of ice, football

Lquids: water, honey

Gases: none are specified – animation shows the clouds (of liquid water droplets) forming around a kettle spout, and 'gas' put into in fizzy drinks is referenced.

A football is not solid, but usually air (a mixture of gases with some other components) contained in a plastic shell. (The voiceover refers simply to a 'ball', but the animation show a large ball with a traditional football pattern being used to do 'keepy uppies' by the cartoon character.)

Honey is not a liquid_(scientific) but a complex mixture of sugars in solution. There is usually much more sugar than water. (So, arguably, it is more solid than liquid – but it is better to simply not consider it as either.) This is where I dropped a mark on the terminal test:

Two of the options are NOT liquids. Only one response gets credit in this test!

Web text:

The bullet points on the site list some further examples:

"Examples of solids include ice, wood and sand." (Ice and sand are solids_(scientific).)

"Examples of liquids include water, honey and milk." (Only water is liquid_(scientific) here.)

"Examples of gases include steam, helium and oxygen." (³/₃, well done BBC!)

Sorting task:

The BBC website task invites children to sort cards showing objects into three categories. (What is that object on the front card meant to be?)

In the sorting task, children are asked to sort a number of examples shown on cards into solid, liquid, and gas:

The examples presented are air, a feather, helium, milk, a pencil, sea, steam, syrup, wood. Of these only helium and steam strictly meet the criteria for being a solid_(scientific)/liquid_(scientific)/gas_(scientific). Yet, as suggested above, it is difficult to find genuine examples that are both scientifically correct and familiar to young children. Perhaps sea and air (at least materials) are closer approximations than a pencil or a feather ("solids retain their shape" – would a child using the website have handled a feather, and, if so, would it have retained its shape under child-handling?)

So, I still have reservations about this material, whilst acknowledging the need to balance scientific correctness with relevant (to children) examples. Strictly, some of the examples can be seen as encouraging children to get the science wrong. These things matter if only because children are learning things on this site that later in their school career will be judged as alternative conceptions and marked as wrong.

(Read 'Are plants solid?')

None the less, I am pleased that the BBC has at least decided to amend its sorting task, and remove the poor cat:

Which pile does the cat belong in? [This example has now been removed. Bravo.]

The website had previously been quite clear that putting the cat as anything other than solid was 'wrong'. It is classed as a solid even though a cat (like any animal) is (or would be if separated out into its constituent substances – and children should not try this at home) more water than anything else.

I had real trouble seeing how that example fitted with the criteria specified on the webpage:

"[Cats] stay in one place and can be held.
[Cats] keep their shape. They do not flow like liquids.
[Cats] always take up the same amount of space. They do not spread out like gases.
[Cats] can be cut or shaped."
Characteristics of solids, but perhaps not entirely true of cats?

* cf. the idiom 'disgusted of Tunbridge Wells' – referring to a hypothetical person who writes to media complaining about matters of concern.

Images used here are screenshots, copyright of the BBC – a publicly funded public service broadcaster.

Gases in bottles try to escape; liquids try to take the shape

Keith S. Taber

Bill was a participant in the Understanding Science Project. Bill, a year 7 (Y7) student, told me that:

"Gases, they try and fill whole room, they don't, like liquids, they stay at the bottom of the container, but gases go fill, do everywhere and fill, try and fill the whole thing."

When asked "Why do they try and do that?" he replied that "Erm, I'm not sure." I suggested some things that Bill might 'try' to do, and asked "so when the gas tries to fill the room, is it the same sort of thing, do we mean the same sort of thing by the word 'try'?" Bill appreciated the difference, and recanted the use of 'try':

"No, I think I phrased that wrong, I meant that it fills the whole area, 'cause it can expand."

However, it soon became clear that Bill's use of the term came easily, despite accepting that it was misleading:

Okay. So it's not, the gas does not come in and say, 'hm, I think I'll fill the whole room', and try and do it?
No, it just does it.
It just does it?
It tries to get out of everywhere, so if you put it in the bottle, it would be trying to get out.

And later:

…are there particles in other things?:
liquids, yeah there is particles in everything, but liquids the particles move quite a lot because, well they have, oh we did this this [in the most recent] lesson, erm, they have energy to move, so they try and move away, but their particles are quite close together.
What about the gases?
The gases, their particles try to stay as far away from each other as possible.
Why is that? Don't they like each other?
No, it's because they are trying to spread out into the whole room.

And later:

…and you said that liquids contain particles? Did you say they move, what did you say about the particles in liquids?
Er, they're quite, they're further apart, than the ones in erm solids, so they erm, they try and take the shape, they move away, but the volume of the water doesn't change. It just moves.
What about the particles in the gas?
The gas, they're really, they're far apart and they try and expand.

Bill had only learnt about particles recently in science, but seemed to have already developed a habitual way of talking about them with anthropomorphism: as if they were conscious agents that strived to fill rooms, escape bottles, and take up the shape of containers.

To some extent this is surely a lack of familiarity with objects that can have inherent motion without having an external cause (like a projectile) or internal purposes (like animals) and/or having a suitable language for talking about the world of molecular level particles ('quanticles'). Such habits may be harmless, but it is a concern if such habitual ways of talking and thinking later come to stand for more scientific descriptions and explanations of natural processes (what has been called strong anthropomorphism).

Bill's lack of a suitable language for talking about particle actions could act as a learning impediment (a deficiency learning impediment), impeding desired learning.

Are plants solid?

Keith S. Taber

Bill was a participant in the Understanding Science Project. Bill (a Year 7 pupil) told me Bill talked about how in his primary school he had studied "a lot about plants, and – inside them, how they produce their own food", and how "inside, it has leaves, inside it, there is chlorophyll, which stores [sic] sunlight, and then it uses that sunlight to produce its food."

Bill had been talking to me about particles, and I asked if plants had anything to do with particles:

Well in the plant, there is particles….'cause it's a solid…. inside the stem is, 'cause going up the stem there would be water, so that's a liquid. And, it also uses oxygen, which is a gas, to make its food, so. I think so.

I suspect that Bill's reference to the plant being "a solid" would seem unproblematic to many people, especially as Bill recognised the presence of water (a liquid) and oxygen (a gas) as well.

There is however a potential issue here. The model of states of matter and changes of state taught in school strictly refers to reasonably pure samples of particular substances (so water is a liquid at normal temperatures, and oxygen is a gas – although strictly speaking the air in which it is found is a mixture which is not best considered 'a gas'). A plant (like an animal) is a complex structure which cannot be considered as a solid (and indeed living things were separated out in distinct substances, water would make up much of the content).

If the scientific model of solids, liquids and gases is applied beyond the range of individual substances, this is sometimes unproblematic. To consider the air as a gas, or the sea as a liquid, is not usually a problem as it is clear what this means in everyday discourse. But of course it is not possible to find 'the' boiling point of complex mixtures such as these.

However a wooden stool is only a solid in the everyday sense, certainly not in a scientific sense, and to refer to animals or plants as solids does considerable violence to the concept. (BBC Bitesize – please note!*)

(* Read 'Thank you, BBC: I'll give you 4/5')

So if someone was stood here, we'd be a solid

Keith S. Taber

Morag was a participant in the Understanding Science Project. During her first term in secondary school, Morag told me she had studies changes of state, which was about "melting things, it's like solid, liquid and gas. Where like an ice cube melts to go to water, it evaporates to go to gas, it then condenses to go to water and then freezes to go to ice".

When I asked her about about the states of matter, Morag gave me a quite polished response. In the middle of this, she stood up and started moving about. It appeared that she had modelled the states of matter in class through a simulation, with the students acting as particles – and this association seemed to now be cued by her recalling the explanations for the different states of matter:

I: So silly question, 'cause I'm sure everybody knows really, but what's a solid, what's a liquid and what's a gas then?
Morag: A solid is an object where the particles are very close together, but still have room to move very slightly, you know like they can only move little bits, er, it has a fixed shape, it cannot be poured – and that's all I can remember.
I: That's quite a bit. And that's different to a liquid, is it?
M: Yeah, 'cause a liquid you can pour, it takes the shape of its container, the particles are spread out more evenly, but still in a, but are still spread in a – yeah they're spread evenly it can be poured, (it takes the shape of its container), the particles are still quite close, but they are further away than they were in a solid, so they can move just a bit more. If you know what I mean, like. So if someone was stood here [indicating next to her], we'd be a solid, 'cause we just move very slightly,
I: all right, yeah
M: and if we were a liquid we would be stood just a bit further away, so we can move a bit more.
I: I see, so if you had brought a friend with you,
M: Yeah, and if we were stood like that, if she was stood there, we'd be a solid, 'cause we were quite close, but we still had room to move about
I: Mm
M: if we were a liquid, we'd be a bit further, but we still, still quite close, but still had move to room, to move about, and I'm not going to tell you about gas until we get onto gas.
I: Okay. So you and your friend could be a liquid? Which means that I could pour you and you would take up the shape of your container?
M: No, I mean like we'd be the particles in liquid.
I: Ah, I see.
M: you know like
I: Moves around!
M: like, so like, like, so we'd be like that, and there would be lots of us, but we could still move about. Yeah? And if we were a liquid we would be like that, and we could still move about. And if we were a gas we'd be further apart, but and then we can, and then we can move around the room freely.

Gas particles like to have a lot of space, so they can expand

Keith S. Taber

Derek was a participant in the Understanding Science Project. I interviewed Derek when he was in Y7 of the English school system. We had been talking about work that Derek has been doing in his science classes on burning. As part of the conversation, Derek defined a solid in particle terms:

what's a solid then, what's a solid?
Lots of particles really close together that can't move a lot.

When I followed this up, Derek explained how a liquid or gas was different to a solid:

And you say solids are made of particles. What are liquids then, they are not made of particles then?
No they are, they are just more spread out particles. And then, you get a gas, which the particles can move a lot more than solid and liquid, they can move wherever they like.
And where do they like to move?
As far away from each other as possible.
Why do you think that is?
'cause they like to have a lot of space, so they can expand.
Why do you think particles like to have a lot of space?
(Pause, c.3s)
Don't know.
Are they unfriendly lot, unsociable?
(Pause, c.2s)
No, they just, they like to have, like be as well away from each other as possible.

The question "where do they like to move" was couched in anthropomorphic terms to reflect the anthropomorphism of Derek's statement that gas particles could "move wherever they like", to see if he would reject the notion of the particles 'liking'. However Derek did not query my use of this language, and indeed suggested that the particles "like to have a lot of space".

When he was asked why, there was a pause, apparently suggesting that for Derek the notion of the particles liking to be far apart seemed to be reasonable enough for him not to have thought about any underlying reason, and his "don't now" was said in a tone suggesting this was a rather uninteresting question. Although Derek rejected the suggestion that the particles were 'unfriendly', 'unsociable' his tone did not suggest he thought this was a silly suggestion: rather it was just that the particles "like" to be as far "away from each other as possible".

The use of anthropomorphism is very common in student talk about particles. Whether or not Derek really believed these gas particles actually had 'likes' in the way that, say, he himself did, cannot be inferred from this exchange. But, in Derek's case, as in that of many other students, the anthropomorphic metaphors seem to offer a satisfactory way of thinking about particle 'behaviour' that is likely to act as a grounded learning impediment because Derek is not open to looking for a different kind (i.e., more scientifically acceptable) type of explanation. Given the common use of his language, it seems likely that it derives from the way teachers use anthropomorphic language metaphorically to communicate abstract ideas to students ('weak anthropomorphism'), but which students accept readily because thinking about particle behaviour in terms of the 'social' models makes sense to them ('strong anthropomorphism').

A cloud is a gas you can see

Keith S. Taber

Bill was a year 7 student who participated in the Understanding Science Project. Bill was explaining that he had been learning about the states of matter, and gave me examples of things he considered to be solids, liquids or gases. I asked him about clouds, because students commonly consider them gases:

So do you think everything, is either a solid, or a liquid or a gas?
I'm not sure? Erm, I think that, some, I think that they are mainly, fall into a group, but I'm not sure.
Not sure about that, okay. Erm, what about a cloud? You look at a nice sky, and there's a cloud? Do you think that's a solid, or a liquid or a gas?
I think that that's a gas that you can see, because it is made up of, I think it is made up of different gases, I'm not sure, though.

Gases are transparent and so generally not visible. A cloud is opaque, and is made up of many tiny droplets of liquid (water in the case of the clouds in the earth's atmosphere) that have been formed by condensation. However, because they remain in the air (until it rains!), it is understandable that students may hold the alternative conception that they are gases themselves. Liquids are much more dense than gases, so it is not immediately obvious to students how a cloud of liquid drops can remain 'floating' in the air. That Bill offered a tentative answer and was not strongly committed to the idea of clouds being gaseous, suggests he was open to revising this view given new evidence to consider.

Read about learners' alternative conceptions