Lab Report Osmosis on Potatoe

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  • Topic: Concentration, Osmosis, Laboratory glassware
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Practical Work Nº2: “Different methods to control osmosis”

Aim: observe and test the process of osmosis through different kinds of methods: the weigh (potato), the density (beetroot) and under the light microscope (onion).

Hypothesis: according to the encyclopedia definition osmosis is the diffusion of a liquid (most often assumed to be water, but it can be any liquid solvent) through a partially-permeable membrane from a region of high solvent potential to a region of low solvent potential. Thus, this is what will happen.

Teacher’s instructions:
▪ We shouldn’t forget to include the experimental error in the results exposed in the recollection of data. ▪ How to prepare a dilute solution from a more concentrated one: Vf . Cf = Vi . Ci

▪ We should do every experiment twice, in order to check the results.


Materials: potato tuber (large), boiling tubes with stoppers x 12, boiling tube rack, scalpel, a pair of tongs, 2 pipettes (± 0,1ml), balance (±0,1g), 2 beakers, marker, sucrose solutions (0.0M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M), distilled water, filter paper, cork borer and Erlenmeyer flask with stopper.

Teacher’s instructions:
▪ The initial mass of every piece of potato should be similar and even. ▪ In the graphs, instead of joining all the points, having as a result a gorge line, we should draw the best fit line, thus having as a result a straight line.

▪ First of all, calculate the amount of distilled water and sucrose solution each test tube had to contain (twice the same), with the formula: 0.0M= 15 ml DW+0ml sucrose sol.
0.1M= 12 ml DW+3ml sucrose sol.
0.2M= 9 ml DW+6 ml sucrose sol.
0.3M= 6 ml DW+9 ml sucrose sol.
0.4M= 3 ml DW+12 ml sucrose sol.
0.5M= 0 ml DW+15 ml sucrose sol.
▪ Using a cork borer, prepare 12 potato cylinders, and place them in an Erlenmeyer flask stopper ▪ Meanwhile, label 12 boiling tubes and place the appropriate dissolution on each tube. ▪ Then, take the Erlenmeyer flask to the balance in order to record for each cylinder its initial mass (after having slightly absorbed with a filter paper the surplus liquid.) ▪ Afterwards, place one cylinder on each tube with the different sucrose solutions, stop up and put the twelve tubes in the refrigerator during one day. ▪ Then, remove the cylinders from the tubes in turn, in the same order you inserted them. Remove any surplus fluid quickly and gently using a standardised procedure. Then, reweigh the cylinders and record its mass.


Table 1: osmosis in potato (weighs before and after placing them in the solutions)

|Solution |Initial weigh |Final weigh |
|(M) (±0,1ml) |(g)(±0,1g) |(g)(±0,1g) |
|0.0 |3.8 |4.4 |
|0.0 |3.8 |4.3 |
|0.1 |3.9 |4.2 |
|0.1 |3.9 |4.3 |
|0.2 |3.9 |4.2 |
|0.2 |3.9 |4.2 |
|0.3 |3.9 |4.1 |
|0.3 |3.9 |4.1 |
|0.4 |4.0 |3.9 |
|0.4 |4.0 |3.9 |
|0.5 |4.0 |3.7 |
|0.5 |4.0 |3.6 |

Analysis of the data:

Table 1. Gain or loss of mass on each concentrated solution and the average between both solutions.

|Solution (±0,1ml)|Loss or gain (g) |Average loss or |
| | |gain (g) |
|0.0M |0,6 |0,55 |
|0.0M |0,5 | |
|0.1M |0,3 |0,35 |
|0.1M |0,4 | |...
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