The effects of different salt solutions on potatoes

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The effects of different salt solutions on potatoes

Plan

My aim is to investigate how different concentrations of salt solution affect the movement of water through a partially permeable membrane (osmosis) in potatoes.

Osmosis is the movement of water from a high concentration to a low concentration through a partially permeable membrane. I will add pieces of potato to varying concentrations of salt solution, wait on each solution and then record the results. I will eventually use the results to measure the percentage change in mass of the potatoes.

To gain accurate results, I will have to make the experiment a fair one, to do this I will implement the following:

Wash my hands before preparing any potato samples.

-So no grease, dirt or any salts transfer from my hands to the potato pieces before the experiment takes place.

I will take core samples from the potatoes.

-To ensure maximum surface area for the salt concentration to cover.

Make sure that only my variable factor changes throughout the experiment and other factors stay constant.

Wash all equipment before using them – To make sure no residue left on them affects the results.

There are several factors that would affect my experiment, the paragraphs below identify these factors and explain how I will keep them constant. – My variable factor for the experiment is the salt solution.

I am aware that the experiment will be affected by certain factors; I will try and keep these factors constant so the end results will be accurate and therefore conclusive.

Surface area would affect the rate of osmosis because the greater the surface area the more area the water has to diffuse through. To control this I will try and get exactly the same shaped potato tubes.

Temperature also affects the rate of osmosis, the higher the temperature of the water, the more energy it has to diffuse through the partially permeable membrane therefore speeding up osmosis. I will try to control this factor by getting water for the experiment from the same place.

Prediction and scientific theory

I predict that as the concentration of salt solution increases, the potato core diameter will decrease. Therefore, the % change in diameter will initially increase and then will decrease with a minus percentage.

This is because of osmosis. Osmosis is a case of diffusion in which only water molecules are concerned. It is the movement of water molecules through a partially permeable membrane (in this case, the potato cells) from an area of high concentration to low concentration. Bigger molecules cannot move through the partially permeable membrane (such as starch).

The reason why the diameter of potato will change is because of the net movement of water. When there is less water outside the cells (potato core) or a higher concentration of salt solution, the net movement of water will be from the potato to its surroundings, therefore it will decrease the diameter of the potato. The cells inside the potato are becoming flaccid as the water moves out of them.

But if there were a higher concentration of water on the outside than the inside of the cells, the net movement would be into the cells therefore making them turgid and increasing the diameter.

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Equipment List – (and why I’ve chosen it)

Timer – To measure length of time potato samples are in salt solution

McCartney Bottles (10) – To hold salt solution and potato pieces

Potatoes – Cells inside potato used for water to move in/out of by osmosis

Labels – To write amounts of salt solutions on, and original mass of potato pieces to put on containers.

Corer – To take potato cores of the same diameter

Salt solution (Sodium Chloride) – To act as the variable

Electric scales – to measure the weight of the potato samples

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