# A GCSE essay on the effects of osmosis on potato chips in different molar solutions

Essay by The_GingerA+, February 2005

Introduction:

Osmosis is a special kind of diffusion.

Diffusion is the movement of particles from a high concentration to a low concentration until they are spread out evenly. Osmosis is the passage of water molecules from a region of high water concentration to a region of low water concentration through a selectively permeable membrane.

The diagram below shows how water molecules move through the selectively permeable membrane from the region of high water concentration to the region of low water concentration until the concentration is equal on both sides of the membrane.

Water moves between cells in plants by osmosis. Instead of measuring percentage change in mass I could have measured the change in length. However I decided to measure percentage change in mass because it is more accurate than the change in length.

Aim:

The aim of this experiment is to discover what the effect of placing potato chips in different molaric solutions does to the chip's mass.

Prediction:

I predict that the length of the potato chip will increase the most in the 0.0 molar solution because the water concentration in 0.0 molar solution is much higher than the concentration of water in the potato chip. So osmosis will occur from the water into the chip.

Variables:

Controlled Variables:

Potato

Independent Variables:

Amount of Sodium concentrate

How long it is being left

Dependant Variables:

Mass of the Chip

Constant Variable:

Length of chip

Volume of chip

Temperature of solution

Temperature of chip

Preliminary experiment:

We placed 3 potato chips of exactly the same length and size in 3 different concentrations of molar solutions. Then we left the potato chips in the test tubes for 20 minutes, filled with 10cm of 0.0 molar, 0.5 molar and 1.0 molar.

Apparatus:

18 test tubes

18 equal size potato chips

Weighing scales

Ruler

Paper towels

100 cm of distilled water (0.0 molar solution)

100 cm of 1.0 molar solution

Scalpel

How to set out the apparatus:

Primary Experiment Method:

1. First you cut three potato chips as close to the same size as you can, measure them, weigh them and record the results in a table.

2. Then you make 10cm of 3 different molar solutions by mixing distilled water (0.0) with a 1 molar solution. For example to make 0.5 molar you would add 5cm distilled water and 5cm 1.0 molar solution. For 0.1 molar solution you would mix 9 cm distilled water and 1 cm 1.0 molar solution.

3. Leave 1 potato chip in each test tube, make sure you have marked which one is which.

4. After about half an hour take your potato chips out, dab them dry, measure them, weigh them and see how much they have changed and record the results in a table.

5. Work out how much they have changed and see what solution has made it grow the most and shrink the most.

Results for Preliminary experiment:

Molar

(m) Length Before (cm) Length After

(cm) Mass Before

(g) Mass After

(g) %

Mass Change

0.0 3.5 3.7 2.6 2.15 + 34.6

0.5 3.5 3.4 2.4 1.73 - 27.9

1.0 3.5 3.4 2.9 1.66 - 42.8

In my proper experiment I will use six different molar concentrations, they will be: 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0.

Proper Experiment Method:

1. First you cut eighteen potato chips (three for each concentration) as close to the same mass as you can, weigh them and record the results in a table.

2. Then you make 10 cm of six different molar solutions by mixing distilled water (0.0) with a 1 molar solution. For example to make 0.5 molar you would add 5 cm distilled water and 5 cm 1.0 molar solution. For 0.1 molar solution you would mix 9 cm distilled water and 1 cm 1.0 molar solution.

3. Leave 1 potato chip in each test tube, make sure you have marked which one is which.

4. After about half an hour take your potato chips out, dab them dry, weigh them and see how much they have changed and record the results in a table.

5. Work out how much the potato chips have changed and see which solution had made it grow the most and shrink the most.

Results of proper experiment:

Molar

(m) Mass Before

(g) Mass After

(g) %

Mass Change Average % Mass Change

0.0 2.56 2.73 +6.64

6.76

2.56 2.74 +7.03

2.57 2.74 +6.61

0.2 2.55 2.54 -0.39

-0.78

2.56 2.54 -0.78

2.56 2.53 -1.17

0.4 2.50 2.23 -10.80

-10.5

2.56 2.30 -10.40

2.52 2.26 -10.30

0.6 2.56 2.17 -15.23

-16.31

2.57 2.20 -16.8

2.56 2.19 -16.9

0.8 2.51 2.03 -23.6

-24.2

2.57 2.07 -24.2

2.57 2.06 -24.8

1.0 2.55 2.05 -24.4

-25.83

2.58 2.03 -27.1

2.52 2.00 -26.0

My results are also shown in the graph below.

From the graph above you can see that the water concentration of the potato chips is between the 0.0 molar and the 0.2 molar solution. You can see this because at the 0.0 molar the potato chip has gained mass and at the 0.2 molar solution the chip has lost mass. This means that at the 0.0 molar solution osmosis has occurred from the solution to the chip, this is why it has gained mass, and in the 0.2 solution osmosis has occurred from the chip to the molar solution, which is why the chip has lost mass.

From the results above the potato chip had gained mass in the 0.0 molar solution, however after that the potato chip steadily lost mass as the concentration of the molar solution increased.

How accurate are my results?

My results are quite accurate, however they are not totally accurate because some of the chips are slightly different masses, also to find the average mass I had to find the mean of the three masses. This meant that the results were slightly off but they are not off enough to make much of a difference as you can see because the points on the graph follow a pattern.