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Osmosis Investigation

Introduction & Aims

At present I am investigating Osmosis, and I have devised a experiment to investigate the rate of it. I have been provided with potatoes, and all the common laboratory equipment.

I will look at 2 variables, one discontinuous, one continuous.

For my discontinuous veritable I have chosen TYPE OF POTATO.

I will have 3 different types of potato, chosen randomly, and numbered A, B & C.

For my continuous veritable I have chosen TIME.

Every 5 minutes, I will record the mass of the potato chip, along with the length.

I hope to be able to carry out this investigation, and produce some accurate results, to conclude my investigation.

My Hypothesis

I think that the rate of osmosis in each of the types of potatoes will be virtually the same. As some potatoes have a different texture, the results will not be exactly the same. I think the colour of the potato chip may have an influence on the rate of osmosis. From past experiments I think the each chip will lose on average around 0.25g in mass, and 4mm in length. The longer the potato is in the solution, the more the mass will rise until all the solution is absorbed into the potato.

Method

• I took 3 potatoes and labelled them A, B & C
• From each I cut a cylinder chip using a tool
• Using a ruler I made sure the length of the chips were the same
• I weighed each of the chips to the highest level of accuracy - (2 d.p.)
• I then measured the chips in mm
• I took 3 test tubes, for the chips A, B & C
• and filled each with 10cm³ of 1 molar sucrose
• I then inserted the correct chip in the correct test tube,
• and started the timer.
• Every 5 minutes I...

a.     removed the sucrose & chip from the test tube,

b.     dried the chip on a paper towel,

c.     weigh the chip to the nearest 0.01g,

d.     measured the chip to the nearest mm

e.     reinserted the correct chip in the correct test tube,

f.       poured the sucrose back in the test tubes,

g.     and restarted the timer.

• This process continued for 25 minutes and was repeated five times

Results

Appearance Before:

A : Pale Yellow

B : Cream

C : White

Note:

I did not make sure the masses were the same, as they all turned out to be the same mass, shows they have the same density.

Mass & Length Loss

Mass Length

Chip A: 0.16g 3mm

Chip B: 0.18g 3mm

Chip C: 0.15g 3mm

Mean: 0.16g 3mm

Conclusion

The 3 types of potato reacted virtually the same as each other, with only about 0.04g difference at the end of 25 minutes, which was probably due to the results being slightly inaccurate as the three chips could not be taken out, weighed, and replaced at once.

The graph shows the chips slightly took a different rate from each other during the 25 minutes.

When the A & B lines where observed carefully, they appear symmetrical, if a line would have been drawn between them, e.g.

THE LINE OF SYMMETRY IS THE DASHED LINE

C makes a smoother curve.

Chip C that was the whitest is colour, lost less water as the other two; this shows the chip must have contained more water than the others. Therefore, higher concentration of water, less water goes in the cells.

Chip B that was the yellowiest is colour, lost more water as the other two; this shows the chip must have contained less water than the others. Therefore, lower concentration of water, more water goes in the cells.

Chip A was in the middle of these two.

Length Change

There was some length change during the experiment, but unlike the mass, all 3 chips decrease at the same rate.

Final Conclusion

My conclusion is virtually the same as my hypothesis, as all the chips have stayed virtually the same as each other.

I could have done the done the experiment again, with more variables, and measuring different aspects of the chip before, e.g. Starch & water content.

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