Research 3

Developing a Constructivist Approach for the Teaching of Particle Theory

Simon Elliott

Developing a constructivist approach for the teaching of Particle Theory: Students’ preconceptions and their cognitive assessment

Simon Elliott, 20th March 1998

Abstract

Understanding the accepted high-school model of particles is an essential tool in the development of more detailed concepts which make up the framework of materials science. Without this fundamental model it would be difficult for students to have a real understanding of matter and its properties on the microscopic scale.

The problem that seems to arise is when this topic is presented to high-school students; too early and they do not have the cognitive skills to deal with the concepts; too late and their preconceived ideas concerning the nature of matter are too deeply entrenched in their minds.

This research endeavours to investigate the cognitive level of students with specific regards to the particulate theory of matter in a quantitative way. It will use an analysis of their responses through the SOLO Taxonomy in order to develop an approach for assessing the most appropriate stage in which to introduce the topic in the high-school science programme. It will also look at the conclusions drawn from existing research.

Introduction

Before considering the specific case of particle theory, I will consider what research has shown about the most appropriate and effective methods for teaching complex and demanding abstract scientific concepts.

Woloshyn comments that;

“Many students demonstrate inadequate understanding of basic scientific concepts even after extensive education.........students believe that science is something done by someone other than themselves”

She noted that many science resources concentrated on activities of lower cognitive demand (retention and comprehension) rather than using higher-order activities (application, analysis, synthesis and evaluation) and thus were less prepared for coping with concepts that made a higher cognitive demand.

Nussbaum and Novick, showed that students were unlikely to assimilate new ideas into their conceptual repertoire until they had been convinced that their preconceived ideas were either wrong or inaccurate. They suggested three phases of acquisition;

1. Acknowledgement and rationalisation of existing beliefs

2. Conflicting event that challenges belief

3. Supported search for scientifically accepted beliefs

This work is made clearer by that of Lichtfeldt who notes that;

There are other relevant influences on learning: motivation is necessary and science ideas have to be fruitful and plausible. Additionally, students’ cognitive structure of their science world has to have a dimension of truth. If students are to accept the science view then they must recognise that their former knowledge is not wholly correct. Thus it is possible that, even where students are well motivated they do not change their concepts but often pick out bits of knowledge to integrate into their previous understanding.

The problem of existing concept structures and beliefs has been compounded by, as Coble and Koballa comment, the increasing exposure of students to scientifically based theories and ideas through visual media. They write that the teacher must use a constructivist approach to the introduction of new concepts, especially those of a more abstract nature.

These approaches are summarised clearly by Kyle et al. who suggest that the way to improving students understanding comes with the realisation of five key points;

1.Students come to classes with ideas

2.Students’ ideas are often different to those of the scientific community

3.Students’ preconceptions are often strongly held

4.Traditional instruction does not lead to substantial conceptual change

5.Effective instructional strategies enable teachers to teach for conceptual change and understanding.

Particle Theory

Taking these findings into consideration, it is surprising to read the work of Fensham who notes that there is not a unified approach to the introduction of chemistry education in high-school science but in-fact three;

1. Substances (materials)

2. Chemical Reactions

3. Atomic Structure

The first two are the most common beginnings to chemistry education where science is begun earlier in schooling, whereas the latter is more common in courses starting at around fourteen years of age.

One American High-School Chemistry course begins with the model of the atom and moves onto examples of reactions and properties of atoms and different combinations of atoms. In the UK the Nuffield approach places the introduction of the concept of particle theory at the end of the course (even after the study of the elements and the Periodic Table) and begins with the different types of reactions.

Leaving particle theory to the latter parts of a course is often because it is a body of concepts thought too hard for many students to cope with. Nussbaum2 showed that most students brought with them to class a continuous model for the nature of matter and therefore, taking constructivist principles into consideration, had problems accepting the discontinuous world that particle theory describes. It was postulated that one possible cause for this was the lateness of the topic’s inclusion in most secondary science courses and the concentration in the years beforehand on the macro-properties of materials science. This leads to students building up conceptions of matter into simplistic forms such as the “block of aluminium” or the “balloon of gas”.

Berkheimer et al. points to the fact that most empirical chemical contexts develop macro-level concepts and thus do not enable students to use such contexts for visualising and rationalising micro-level concepts where instruction of such concepts are left until later in the course. In other words, if students are not presented with an atomic model for matter before studying materials, their properties and reactions, they will develop a firmly embedded continuous macro-model for matter. The science educator will thus have four or more years of reinforcement to overcome when challenging their pre-conceived ideas with a new discontinuous micro-model.

Perhaps some of the most important work done on developing a constructivist approach to the instruction of the topic of atomic theory has been conducted in a long term research project in a Berlin gymnasium reported by Lichtfeldt and in the work of Driver.

Lichtfeldt describes work done on the effect of different course structures on the development of coherent ideas about atoms in his research project “Pathways to the Atom-idea”. He found that many students were bringing with them a well-developed concept-collection around the key idea of “Atom”. The source of their ideas was from a wide variety of textual and other materials and, even as young as Grade 7, students had firm ideas about “atoms” and these had to be addressed by the teacher introducing the topic formally.

This pre-lesson-knowledge was found to act as either a barrier or a motivator but, in either case had to be considered by the teacher in order for the students to move to science-knowledge through some form of conceptual change.

What this long-term research project has shown is that the use of “particle” and “atom” in discontinuous micro-models by teachers is often confused and muddled and leads to confusion on the part of students who find it difficult to differentiate between models. Because these models are muddled and do not effectively integrate into students’ understandings of matter, they then have a tendency to fall back onto this continuous model later in their studies. The knowledge has not been retained.

The research did show that the approach of the teacher to the topic was fundamental in the quality of the students’ understanding. There was a clearly demonstrated need for teachers to understand the conceptual framework that students were bringing with them to the lessons (their “everyday-knowledge structures” as Lichtfeldt calls them) and teach through modified versions of these. Thus a step-by-step approach to the topic was shown to have far greater effect in concept retention.

Some of the work of the Making Sense of Secondary Science project looked at students’ concepts of particles. Driver et al. conducted an extensive review of the research done on this topic and showed that;

Students found difficulty in developing an adequate conception of the chemical combination of elements until they were able to interpret combination at a particulate level.

Without sufficient grasp of the discontinuous nature of matter, students are not able to look at phenomena such as the reaction between hydrogen chloride and ammonia gases and truly understand the nature of the chemical combination that they can see in front of them.

Piaget noticed that there were striking changes in the development of a child’s thinking on matter when comparing children of four and five years of age with those of eleven and twelve. He used the simple experiment of the dissolving of sugar to investigate a child’s reaction to the apparent disappearance of the material. The main change was in the use of theories outside the subjects’ normal experience in their explanation for the observed phenomenon after the ages of 8 to 9 years perhaps showing a predisposition to accepting a particulate view of matter towards the beginning of the Secondary School system (Year 7).

The Project

If one is to include an particle theory model in the 11-16 curriculum then it is important to have generalised information on when students reach the required cognitive level to assimilate the concepts into their understanding. It would also be useful to develop a tool for assessing particular groups or individuals in order to more closely fit the topic to the group or individual in question.

It is from this starting point that this project is based. In order to investigate this area in a new way and not merely repeat past work, it is necessary to look at the research methods already used. Piaget, Holding, Driver,, , ,, , Novick and Nussbaum3 and Ben-Zvi et al. have all conducted extensive research into this area as well as the ongoing work of Lichtfeltd4 already mentioned.

Piaget described particle theory as being outside first-hand reality therefore, as a subject cannot deduce the theory from directly observable phenomena, Piagetian theory would place particle theory as being in the Formal Operational cognitive level. Karplus suggest however that, as particle theory has a clearly defined language that can be learned, it could be described as concrete operational.

Piaget’s research, perhaps because of his roots in zoology, was based largely on observation of subject’s responses to situations or phenomena. His conclusions were drawn from clinical evidence where the approach was highly subject-focused and flexible, changing to investigate the subtleties of each child’s response. Whilst this is the ideal methodology to tackle cognitive assessment, a standardised system is more realistic for the normal classroom and for the short time-scale under which this project would need to operate.

Holding used a similar approach to Piaget with the characteristic scenario-with-questions as a method for analysing a subject’s cognitive skills. One interesting scenario was connected with Holding’s study into student’s perceptions of the particulate nature of matter and the age at which this conceptual model was arrived at within the student’s cognitive vocabulary.

Students were shown a set of scales with a glass of water and a bowl of sugar in each pan. They were asked to say what they thought would happen to the scales (which were balanced) if the sugar on one side was tipped into the water. Their response was then analysed for the level of cognitive complexity. A summary of Holding’s findings is in the following table;

Age

Complexity of particulate model

7 - 9

Sugar still there, just hidden in water

9 - 11

Sugar is still there but broken into small particles

11 - 14

Particles not just “little bits of sugar”

14 - 16

Increasing complexity of model

Holding thus identified the major changing point in a student’s development of a particulate nature for matter as 9 to 11 years of age.

The major research performed on the specifics of student’s cognitive development with regards to science education has been performed by Driver et al. over a number of years. A study of some of the articles produced show the use of the analysis of audio and video recordings of student’s reactions to observed phenomena as a way of judging their cognitive skills as well as written and typed tasks that demand a response to a scenario.

The work produced a number of important tools for the researcher and educator concerned with cognitive development in science;

Evidence of subjects’ conceptual change in particle theory sees the involvement of accepted particulate models in reasoning about observed phenomena.

There is evidence of the student’s independent development of a particulate nature of matter between the ages of 10 and 12 years and this is when their ideas can be reinforced or overwritten by the approach of the educator to materials science (macroscopic or microscopic).

The constructivist approach to a topic involves the use of pre-testing in the development of the curriculum for a group or individual in order to draw out preconceptions and thus deal with them “out in the open” within the following topic.

There are two main learning processes in the classroom, the former of which is more successful;

1.Inside-out: learner modifies own beliefs after observing challenging phenomena

2.Outside-in:learner modifies own beliefs after instruction from an educator.

Novick and Nussbaum came to similar conclusions after using research based around interviews after observed phenomena. They concluded that the best approach to teaching the nature of matter relied upon attempting to shift students’ understanding about particle theory by first brainstorming perceived ideas and then using observable examples and demonstrations to refute erroneous theories and reinforce correct ones.

Ben-Zvi et al. showed that students had difficulties visualising what was meant by “particle” even at the end of a high school science course. When used in the context of chemical reactions that had moved from a macroscopic description (word formulae) to a microscopic description (symbolic formulae), students showed difficulties describing the particulate interactions. This research approach involved a formal question and answer sheet with space for subjects to illustrate their theories.

Lichtfeltd’s work is also based upon questionnaires with responses analysed more closely by the use of one-to-one interviews although a variety of methods were used. Lichtfeldt used two levels of sampling; the detailed study consisted of twenty-four students, six from each of four groups, being video-taped in class and asked to fill in regular questionnaires. They were also interviewed on site about their responses. In addition to this group, the whole cohort of one hundred students (twenty-five from each of four groups were questioned every six months and video-taped once. On completion of the course, ten students were questioned to assess overall conceptual change.

The published results are of a highly qualitative nature and show no breakdown of proportions of students successfully assimilating the particulate/atomic model of matter into their understanding.

Biggs’ Structure of Observed Learning Outcomes (SOLO) Taxonomy gives us a way of interpreting students’ answers to questions in a quantitative way when they would formally have been limited to a qualitative analysis. In avoiding the use of multiple choice questionnaires in this instance, the researcher is more able to extract the subjects’ true understanding of the concept or topic. Ratcliffe summarises the SOLO Taxonomy structure as;

Piagetian Stage

SOLO Description

Response Type

Consistency and Closure

Formal Operational

(16+)

Extended Abstract

(Level 5)

All relevant information is used and related and external information is incorporated. Deduction and induction may be present.

Inconsistency resolved. No felt need to give closed response - conclusion held open. Generalises to situations not experienced.

Concrete Generalisation

(13-15 years)

Relational

(Level 4)

All relevant information is used and the information is related to determine underlying relationships. No external evidence is used.

No inconsistency within the given system, but since closure is unique, inconsistencies may occur outside the system. Generalises within given context

Middle Concrete

(10-12 years)

Multi-structural

(Level 3)

More than one relevant piece of evidence is used. If all relevant pieces of evidence are used, they are used independently and relationships are not seen or stated.

Closure reached too soon; can come to different conclusions with the same data. Generalises only in terms of a few limited and independent aspects.

Early Concrete

(7-9 years)

Uni-structural

(Level 2)

One relevant piece of information or evidence is used in the response.

Closes early, can be very inconsistent. Generalises only in terms of one aspect.

Pre-operational

(4-6 years)

Pre-structural

(level 1)

Cue and response often confused. Fails to realise or see the problem. No evidence or information cited.

Closes without seeing problem. Bound to specifics.

Boulton-Lewis comments that the SOLO taxonomy looks for an increase in the depth of strategy for answering questions and gives a simplified view of the criteria for the SOLO levels as;

SOLO Description

SOLO Level

Response Type

Extended Abstract

Incompetence, nothing known about the area

Relational

One relevant aspect known

Multi-structural

Several independent aspects known

Uni-structural

Aspects are related into a structure

Pre-structural

Knowledge is generalised to a new domain

The methodology of the SOLO taxonomy is described by Biggs who places the proviso on the use of the system that the resultant developmental levels produced by the analysis of students’ responses can only be considered to be valid for that area of study investigated. Biggs goes on further to describe the methodology behind using the SOLO Taxonomy as a research tool.

In this project I intend to sample from each of the five year groups in the English secondary school system, (National Curriculum years 7-11). In each of these year groups I will test twenty students from across the ability range giving a total sample of one hundred responses. In this way I will be able to assess a mean level for the year-group with the level-range and look at the progression of cognitive ability across the year-groups. The sample will be same-gender but further sampling would look at a comparison between gender groups and calculations of mean levels for mixed-gender groupings.

By using a random selection of four or five pupils from within each of the five or four ability groupings within the year I will be using the probability sample stratified sampling technique. This will ensure that I have covered the ability range thoroughly, although a sample of this low size does perhaps place too much of a strain on the homogeneity of ability setting in secondary schools.

Each subject will be asked to respond to three passages that give evidence that one could use to suggest the existence of particles. They will then be asked to respond to this passage and describe what they infer from it. It is these explanations that will be assessed for evidence of their cognitive ability.

The school in which the research will be carried out introduces the concept of particle theory in year 9 and year 11. It will therefore be important to use some form of graphical analysis to assess whether their encounter with the theory in class makes a significant change to the level of their responses in cognitive terms.

I will trial part of the test material (the first question) with a small group in order to identify possible problems with the material itself. This will take the form of a group of twenty seven year 8 students (twelve to thirteen years old) performing the first of the tasks as planned for the larger selection. I will include the responses within this research plan and any changes that will be necessary to the testing materials before any further research could be carried out.

Passage one consists of a textual description of the dissolving sugar problem similar to one that Holding used, as described earlier. The difference in using text form Holding’s method is that it forces the subject to imagine the situation without direct visual or verbal stimuli.

Sammy puts a glass of water on some scales together with a small dish of white sugar. The total weight reads 120g on the scales. When the sugar is added to the water it sinks to the bottom but can still be seen. Sammy puts the dish back on the scales and notices that they still say 120g. Several hours later, Sammy comes back to the scales and checks the reading again – still 120g but there is no sign of the sugar at the bottom of the glass.

Can you help explain what has happened?

Passage two describes an experiment commonly used to demonstrate diffusion between liquids and thus to lead students to the inference that different substances are made up of particles of different sizes.

Frances has got two measuring jugs each containing 50ml of a clear, colourless liquid. The first jug is the word “ethanol” written on it and the second has the word “water” written on it. The ethanol in the first jug weighs 39.47g and the water in the second weighs 50g. When Frances pours the water into the first jug with the ethanol, the group watching are surprised to see the reading on the side of the jug has changed to 95ml and not 100ml as they expected.

How could Frances explain what has happened to the rest of the group?

The final passage looks at the reaction between iron and sulphur and how the properties of the separate elements are lost when they combine to form iron sulphide.

Asha is looking at two different substances in her science lesson. The first is a yellow powder called sulphur and the second is a silvery-grey powder called iron. When she places a magnet in the jar of sulphur, nothing happens but when she places the magnet in the jar of iron powder, lots of it sticks to the magnet. After writing down what she has seen, she tips a little of each powder into a dish and stirs them with a glass rod until they are mixed together. The new powder is a mix of yellow and grey and, when she pushes the magnet into the mixture and pulls it out, it is covered in a silvery-grey powder. After writing all of this down, she tips a little of the sulphur and iron powders into a test-tube and heats the mixture strongly using a Bunsen burner. After a short while the mixture begins to glow bright orange even when Asha takes it out of the flame so she places the tube in a rack and watches it until the glow disappears. Once the tube has cooled, she tips the contents out onto a mat and pushes the magnet into the dark-grey powder. When she pulls the magnet out, there is nothing sticking to the end of it.

What should Asha write as an explanation for what she has seen?

Summary of results from the trial group

The responses from the trial group can be loosely fitted into a number of categories in terms of the particulate nature of the explanation.

The first group of responses tried to explain the event but involved no particulate explanation at all. They simply stated that the sugar had dissolved, was still there (no further explanation) and so that was why the mass was still the same) Whether or not the explanation was a valid one, in terms of explaining an event that clearly involved a process on a particulate level, they did not attempt to resolve the disappearance of the sugar in any sort of a particulate way (even to the simplistic level of “little bits of sugar”). Holding’s research would put these replies on a particulate level at less than seven years of age. The SOLO Taxonomy would place this type of response in this context as being at level 1 – Pre-operational. Six responses fell into this group (22%)

There were a small number of replies that simply stated that the sugar had dissolved and that was why you could not see it. Harding’s research based upon a visual exercise would place these responses as being typical for the seven to nine year olds and the SOLO taxonomy would class the responses as falling within the uni-structural phase of Early Concrete. There were twelve such responses within the test group (44%).

The next class of response tried to explain the disappearance of the sugar as being in terms of “granules” or “crystals” of sugar breaking down into smaller bits. It was clear from the responses that they did not consider any form of microscopic particle other than as a small part of the macroscopic substance, sugar. Holding’s research would place this at the nine to eleven age group, the multi-structural phase of Middle Concrete. Within the test group, four responses fitted into this group (15%).

Finally some responses began to invoke a deeper, particulate model for the solution although still on a basic level. It was clear from their responses that they understood to some extent that the sugar “granules” or “crystals” had not just become “smaller granules” or “smaller crystals” but that the macroscopic structure had broken down to release microscopic parts. Holding’s research places this at the eleven to fourteen age group, the relational phase of Concrete Generalisation in the SOLO taxonomy. Five responses fell into this category (19%).

To summarise;

Phase

Solo Description

Piagetian Level

Holding’s Ages

% responses

Pre-structural

Pre-operational

Uni-structural

Early Concrete

7-9

Multi-structural

Middle Concrete

9-11

Relational

Concrete Generalisation

11-14

Conclusions drawn from the trial

From the responses to the described event, it is immediately apparent that there is a wide range of responses even from a single class of twelve to thirteen year old students. Only nineteen percent used any real form of particulate model of a level commensurate with their age group and this is after five terms of secondary school education with 200 minutes of science lessons each week.

The test material must therefore come under closer scrutiny to check that it was not the passage that hindered the pupils. The passage itself has a Flesch readability score of 79.5 placing it at a reading age of around twelve. Some work could be done to reduce this further. It was also clear from the responses that the majority of pupils missed the significance of the dissolving of the sugar over a period of several hours. Although stirring (or lack of it) was not mentioned, some subjects may have assumed that this had happened. The passage should be changed to make this clear.

This type of testing of students’ cognitive abilities does also assume that they are competent at recognising the need for an extended answer. It could be that those who answered in the form of “the sugar had dissolved” did not see the need for any form of explanation for such a commonplace event and certainly did not utilise a complex particulate model when one was not asked for.

It must therefore be asked whether testing of the sort performed in this research that relies on written answers to textual or even visual stimuli to assess the cognitive ability of an individual can be used as the sole method of cognitive assessment.

The analysis of the responses to only one event was time consuming even when performed in an approximate way. If this was to be used to develop an approach to the introduction of particulate theory in a school then it is clear that it would have to be performed as a piece of informative research and not as a form of cognitive assessment for each pupil. It would, however, be a useful tool for assessing the effectiveness of a change of teaching scheme in the before-and-after approach often used by Driver et al. In order to eliminate the effect of one piece of test material, any results from the three pieces mentioned earlier would need to be averaged. A wider sample than twenty-seven subjects in each of the year groups would be required and they would also need to be spread across all teaching groups in order to eliminate the effect of the teacher involved.

Appendix One:Trial group material

Please read the following passage carefully and then write your response in the space below. Please write down all that you think of, even if you are unsure of whether it is correct or not.

Can you help explain what has happened?

........................................................................................................................

.......................................................................................................................

Appendix Two:Trial group responses

Subject 1.

The sugar is dissolved into the water, that is why you can’t see it.

Subject 2.

What has happened is the sugar has dissolved. Even thought the weight is the same, it seems there is no sugar left anymore. There is ! The sugar has dissolved into the water which has increased the mass of the water. Even though the sugar is invisible it’s still present in the water.

Now the mass in the water has increased it makes up for the sugar being not a separate thing anymore

Subject 3.

What has happened is the sugar has dissolved into the water and the mass is still the same as the sugar is still in the water it’s just mixed in and has increased the mass of the water,

Subject 4.

The sugar has dissolved into the water so it cannot be seen but it is still present. The water is made into a sugar solution. Sugar dissolved as it is soluble

Subject 5.

The sugar has dissolved into the water keeping the mass of the water the same, this is why that at the end there is no sugar visable. The water is now a sugar solution. The mass has stayed the same because the sugar has dissolved.

Subject 6.

The sugar dissolved in the water after a period of time but not straight away which meant the solution was the same weight.

Subject 7.

When the sugar was added, the sugar dissolved as sugar is soluble and although you can’t see it, the sugar is still present. The sugar was added and by the time Sammy weighed the solution, the sugar had dissolved keeping the solution the same weight.

Subject 8.

At first the sugar was visable and then it started to dissolve. Several hours later, all the sugar had dissolved and so even though it wasn’t visible you could have still tell it was there if you tasted it because it would be sweet. The glass weighed the same because the sugar was the same except it was in the liquid and not as a solid. At the start you can see the sugar as it is in granules and then nearer the end you can’t see the sugar because it had no colour. If you had used coloured sugar then the water would have changed colour which would be the dissolved sugar.

Subject 9.

The sugar dissolved into the water in the period of time so that is why you can’t see it

Subject 10.

I think the sugar had dissolved and that is why you can’t see it.

Subject 11.

The sugar had dissolved and so the weight stayed the same.

Subject 12.

The sugar is added to the water but the weight is still the same. When Sammy came back several hours later the sugar had dissolved but it was still there, the sugar molecules had been spread about in the water and are so small they cannot be seen.

Subject 13.

The sugar dissolved and so you can’t see it but it is still there and it hasn’t disappeared.

Subject 14.

When Sammy adds the sugar to the water everything is put back on the scales but because the sugar was added to the water no more or no less than before the weight is still the same. The second time, the sugar has dissolved but the weight was still the same as the sugar molecules were still there.

Subject 15.

When Sammy adds the water to the sugar, the water becomes heavier and he puts the dish back on the scales so there is still everything on the scales that there was in the first place so it is still 120g. After several hours, the sugar has dissolved and turned into just sugar molecules (tiny) which you can’t see but which still add up to the same weight.

Subject 16.

I think that what has happened is that after a couple of hours when Sammy went back to the scales, the sugar had dissolved into the water and so you can’t see it but it is still in the water. It wouldn’t have gone down in weight because the sugar is still there in the water

Subject 17.

The sugar had dissolved into the water but is still present. The water is now a sugar solution.

Subject 18.

The sugar had dissolved into the water to make a sugar solution but it is still present. The crystals of sugar have been broken down into smaller pieces and they have joined with the molecules of water.

Subject 19.

The sugar has dissolved in the water. The weight of the water and the weight of the sugar have combined together so the weight has stayed the same at 120g. If the water was hot the sugar would have dissolved quicker but this would not have made a difference to the weight.

Subject 20.

The sugar has dissolved in the water. The sugar must have had longer time in the water to dissolve. The weight has not changed because the sugar molecules are still there even though you cannot see them.

Subject 21.

The sugar has had time to dissolve in the water. It is still present but has been broken down. The weight won’t differ because the water and the sugar are still there even if you can’t see the sugar. If the water had been hot then the sugar would have broken down quicker.

Subject 22.

The sugar has dissolved into the water. This explains why it still weighs 120g. The sugar is still present but the molecules it has broken into are too small to see.

Subject 23.

The sugar has dissolved in the water and this explains it disappearing. Was the water hot or cold? Did someone stir the glass of water?

Subject 24.

The sugar has been dissolved in the water. It did not dissolve straight away because it takes time to dissolve. The experiment may take a shorter amount of time it the water was warmer.

Subject 25.

The sugar has dissolved into the water. The weight has not changed because the water mass has to combine with the sugar mass so it will still be the total of 120g. The water has larger molecules to the sugar so the sugar can dissolve into it. If the particles were bigger then the sugar could not have dissolved.

Subject 26.

The sugar has dissolved into the water because the water is made up of large particles and the sugar is made up of small particles. The sugar particles have fallen into the gaps between the water molecules. The weight hasn’t changed because the water and sugar are both still there.

Subject 27.

The sugar had dissolved in the water and it has turned into a sugar solution rather than solid crystals. The crystals have been broken up and mixed with the tiny molecules in the water which means that it will weigh the same because nothing has disappeared from the water.

Bibliography