An Experiment into the Effect of Sugar Concentration on Osmosis

An experiment into the effect of sugar concentration on osmosis

Background information

Osmosis is the movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane.

The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.

Plant cells do not burst in pure water. This is because the cell is surrounded by a cell wall. This prevents the cell either bursting or losing

its shape too much.

Factors affecting osmosis

Concentration of water-sugar solution. This I have chosen to be my variable. Should the water contain certain amounts of sugar, we can ascertain from preliminary work that the weight of the potato strips should decrease.

Time that the potato should be left in the solution. As long as the period of time is kept constant, one or two days, it does not matter. I suggest that one day would be an acceptable span of time, so as to take measurements of the chips of potato, not long after the osmosis of the potato chips has taken place to its full potential.

Size of potato pieces. From my preliminary work, I have decided that the larger the piece of potato is, the more useful the data obtained from the experiment becomes. This is because if the potato pieces are too small, the change in reading will not be of much consequence, because the scales are not accurate enough.

Surface area. This will affect the speed at which osmosis takes place. If the pieces are all kept at the same length and are in one piece this should keep that factor constant.

Things to consider

I was able from my preliminary work to implement some methodical changes that would aid me in gaining useful results. The first is that the pieces of potato needed to be bigger an cut more precisely. This would in turn give me better and more useful results.

The next factor was the range of results. It seemed that past a certain concentration of sugar solution, the weigth did not seem to change at all. I prepose more measurements at a lower concentration range, as shown on the diagram below.

Apparatus

* Potato

* Distilled water

* Test tubes

* Test tube rack

* Scalpel

* Wooden seeker

* 1 molar sucrose solution

* 5ml syringes

* Accurate scales (100th of a gram)

* Cork borer

Method

* Take potato and push cork borer through it, making sure that you are not holding the potato whilst doing this, but placing on a work surface of some kind

* Remove the bored piece of potato with the wooden seeker, then, using the scalpel, remove any pieces of potato skin on the cylindrical strips of potato. Do this repeatedly

* Accurately divide the strips into seven 5cm strips. Use the scales to check the weights of the potato strips are all 2.0g . Place each strip in a test tube, marked out with its morality of sucrose solution.

* Draw up a in a syringe the following concentrations of water to sucrose. The morality is the way that you should always refer to the solutions.

0.6 mol = 3ml sucrose + 2ml water

0.5 mol = 2.5ml sucrose + 2.5ml water

0.4 mol = 2ml sucrose + 3ml water

0.3 mol = 1.5ml sucrose + 2.5ml water

0.2 mol = 1ml sucrose + 4ml water

0.1 mol = 0.5ml sucrose + 4.5ml water

0.0 mol = 0ml sucrose + 5ml water

Each morality goes into a separate test-tube.

* Leave for 4 hours. Remove the pieces of potato, dry them on a cloth or piece of tissue, so that no fluid is left on the outside of the potato. Weigh each of the pieces separately and make a note of the weight.

* Repeat the experiment twice.

Fairness

If everything is cut exactly, weighs the same and volumes in the syringes are exact, the tests should be accurate. The data obtained can be called reliable if the test is repeated to give a better idea of the spread of the results.

Safety

Do nt hold potato in your hand whilst boring, make sure you do it on a work surface.

Take care when using scalpel, as it is surgically sharp.

When working with glass test tubes, make sure that all bags and chairs are kept out of the way, and do not run, weather or not you are holding the test tubes.

Predictions

I predict that as the water potential outside of the potato increases, so too will the weights. This is because the water molecules pass from a high concentration, i.e. In the water itself, to a low concentration, i.e. In the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations.

I would estimate that as the morality of the solution decreases by a factor of 2 (i.e. 0.6mol-0.3mol) the difference of the weight from the original would be twice as much. I would expect, for example, if the starting weight was 1 gram of potato, and in a solution of 0.6mol sucrose solution, the finishing weight was 0.5 grams, I would expect the 0.3mol solution would give the potato a weight of 0.75 grams.

Morality