Science homework question

[roisin]

This puzzled me as I'm not sure what they are getting at. ds1 has done the homework already and his answer sounds fine to me and no matter what you say I won't get him to change it. But I'm just interested to hear what anyone else thinks about it. What do you think they are looking for?

The homework starts off:
Scientists model ideas by drawing pictures or using logic solutions. Two glass are equally filled with water. Into one, a spoonful of green dye. Is the number of red particles and green particles likely to be the same? Explain your answer.

ds1 has written:
The amount of red dye particles and green dye particles are not likely to be the same as different chemicals have different sized atoms and higher or lower density than others. Also even for the same chemical it would be very hard to measure precisely enough to get exactly the same amount of particles.

[Blandmum]

I'm confused? Where do the red particles come in?

[roisin]

Sorry missed a bit out. Into one, a spoonful of green dye is added. Into the other a spoonful of red dye is added.

Oh, meant to add btw, he is only 11 (yr7) but is a bit of a nerdy science geek.

The homework was a "challenge" and they had to choose which level challenge they did. This is the start of the 'difficult' challenge.

[KatyMac]

Is it something to do with the red particle reflecting green part of the spectrum or has my cold imploded my mind?

[KatyMac]

Obviously not

[Blandmum]

If it is a spoonfull the volume of particle isso huge compared to the size of the particles themselves even the tiniest difference in volume of the spoonful will have a vast difference in the number of partculs.

and he is right. If one particle is bigget than the other, it will have an effect.

Plus, does the dye only contain dye particles? Or are they disolved in a solvent? If so then the concentrations of each may vary

[OhWellNeverMind]

I assume your question forgot theh spoonful of red dye in the other glass.

I wouldn't say what he is written is wrong. Niot a huge amount of difference in atom size...but there would be in compound size (which the dyes are likely to be). I would perhaps exemplify it with an example like, a spoonful of flour has more grains than a spoonful of sugar because the grains are adifferent size. That would probably bring in teh "modelling" that is referred to in the first part of the question.

[cmotdibbler]

But there won't be green dye particles will there ? There will be yellow ones and blue ones in that glass....

[roisin]

I still don't quite understand what the homework is getting at though. Are they just wanting children to try and think creatively and then use logic and reasoning to explain their thinking? Or are they expecting children to research some answers? Or to find out that some (nerdy geeky) children may know some of the facts already?

(The second part of the challenge was rather more straightforward IMO.)

[Blandmum]

I think that it may be asking them to think about levels of accuracy in measurement.

and the effect of compounds being different sizes

and, for that matter, that the dyes are compunds and not atomes of dye IYSWIM

[roisin]

OK, I get the bit about accuracy in measurement and that seems very appropriate for this stage of Science.

But I don't think any of them will know very much about atoms or molecules or compounds at this stage will they? (I'm not very sure what they study at KS2 these days.)

[OhWellNeverMind]

To me (remember non teacher & non chemist), I would say that the statement "Scientists model ideas by drawing pictures or using logic solutions" is just as important as the rest.

I think there should be some evidence of modelling or logic...si I would prob draw a spoon with big circles and one with little circles and show a differenxce in number.

Oh and cmot...dyes can be green...you don't have to mix yellow and blue

[OhWellNeverMind]

If he is not sure of atoms and cpompounds I think talking "particles" is fine.

[Blandmum]

they 'do' atoms in year 8

[SqueakyPop]

I think if they are just trying to find out what kind of scientific brain he has, his answer is very good.

Obviously, there is the inaccuracy about atoms rather than molecules, but he has made the key points - the size of the particles, their density, the crude measuring device, and MB's point, their concentration in the solvent.

[BecauseImWorthIt]

At this age, isn't it just about seeing if they can think through all the likely issues and assumptions? e.g. are all the spoons the same size, are the glasses the same size, is one spoon heaped whereas the other is level, etc - as well as all the 'scientific' issues, such as atoms, etc.

Quite a good way of getting them to think, actually - a question where there can be many different correct answers!