STEM – Blackcurrant Osmosis

Who doesn’t love Ribena? And chips? Okay, maybe not really together as such. I found this experiment through Practical Biology a few years ago, but have only just got around to testing it myself and then putting it into a STEM session. The Practical Biology/Nuffield site have lots of different experiments you can browse through, each with teacher and separate student guidance. I simplified the Blackcurrant Osmosis one for the time and age of the students.

It really is very simple and easy to set up. Also, it’s very visual for students to look at. Here are some of our potato chips after 15-20 minutes in different Ribena concentrations –

Blackcurrant Potatoes

It’s quite obvious which one is 0% Blackcurrant and which is 100%. It’s pretty clear even for the other concentrations. That wouldn’t happen with plain old sugar water, would it?

We did this with a group or KS3 who knew nothing about osmosis, nothing about concentration and had never done a practical quite like this before, but in the hour session they all did pretty well. I think this would be perfectly suited for an hour length lesson especially with the right background knowledge. I would simplify it for a repeat STEM session though and cut all of the chips to perfect size so that step could be cut out completely. I am pretty amazed at how well the year 7s did with making the different concentrations and, from the results, all of the concentrations were made pretty accurately. There was only one group with anomalous results that made no sense!

0% - 80% Strength

It’s all actually quite simple really – make 6 concentrations of blackcurrant squash (from 0% to 100%) (oh, and whilst Ribena works very well, so does the blackcurrant cordial we tried), put a pre-weighed potato chip into each concentration and leave for 15-20 minutes.

Floating Chips

(Note how the chips float with increasing squash concentration. Can you explain that?)

Then, remove each chip, pat them dry and weigh each one again. Then calculate the percentage change in mass.

0% - 100% Chips

The 0% blackcurrant was the only chip to not lose mass as water moved into it from the greater concentration outside of the potato cells. All of the others had water leave the chip via osmosis (to varying extents) as the water concentration was greater within the chips compared to the sugary Ribena.

For younger students, if you leave the chips in long enough they might get enough out of the experiment from just seeing the purple coloured chips. Can they explain it? And then with age/knowledge move on to the theory behind osmosis and the graphing example Nuffield gives.

I’d also like to try their example of altering this experiment to show the rate of water movement. Perhaps that would be better for understanding the basics behind osmosis for younger students.

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STEM – Unlocking the Rainbow

Following on from the Skittles posts recently – Candy Experiments and Fun Experiments. We tried this! Well, we tried the rainbow one again, more accurately this time and we got some amazing results. The Skittles in a petri dish worked just as previous blogs said, some of our STEM Club’s results were amazing –

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We tried it with 3 and 5 coloured Skittles (although I realised far too late that there are not 6 colours of Skittles!) and produced a very simple worksheet for colouring in. I love how the colours don’t mix!

Then we did the density rainbow which certainly involves a very steady hand! But some of our groups managed to make it (after I worried hugely that I had made the solutions wrong!)

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I made a huge batch of the different colours – using 100 red skittles, 75 orange, 50 yellow, 25 green and 5 purple – each in 300ml of just boiled water and left them to dissolve for over an hour. I only opted to do it in that order as somebody I know loves the purple flavour so I saved them! In total we opened 3-4 big bags of Skittles, but it was for a full sized class and there are some left.

I even also now have an extension for this experiment, but it’s an Adults only extension! How about a rainbow of Skittles vodka? Any adult want to try it and let me know how it works?

 

 

Candy Experiments: Skittles Rainbow

Candy Experiments: Skittles Rainbow. As an add on to the post I made yesterday about sweetie science, this is the link I found a few years ago for the density rainbow using skittles. I tried it out without being too accurate in my water measurements and had a bit of trouble with the red and yellow, but the other colours had amazing banding.

I’m going to try it again, with a bit more accuracy and the petri dish skittle experiment. Again, this experiment is easy enough to do at home, too. All you need is skittles, water and cups/glasses (see through ones) and a very steady arm!