Rate of Osmosis

Topics: Concentration, Observational error, Osmosis Pages: 7 (1754 words) Published: September 25, 2013
Abstract

This investigation was undertaken in order to observe the effects of changing the temperature of the solution that a potato cube is placed in. The temperatures that were tested in this investigation were 0°C, 20°C (room temperature), and 70°C. This investigation tested the hypothesis: The rate of osmosis will increase as the temperature increases 2x2x2cm cubes of potato were weighed and then placed into 100mL of 10% NaCl solutions for 10 minutes. After 10 minutes the cubes were again weighed to determine the amount of mass that they lost/gained and thus get an indication of the rate of osmosis. The results collected showed that the rate of osmosis was highest in the 70°C solution and lowest in the 20°C solution. From these results it was concluded that the hypothesis was partially supported as the rate of osmosis was highest in the highest temperature solution, however it was higher in the 0°C solution than it was in the 20°C solution which does not support the hypothesis. Introduction

The purpose of this investigation is to observe the effects of changing the temperature of the external environment of a plant cell on the rate of osmosis. In both uni-cellular and multi-cellular organisms, the control of water is vital. Cells contain both water and dissolved solids and for their efficient functioning, cells must maintain the correct osmotic potential. All living organisms consist of cells and all cells are surrounded by a membrane. One of the cell membranes major functions is to regulate the passage of materials into and out of the cell. Cell membranes are ‘semi-permeable’ which means that some substances can easily pass through them, whereas others cannot. Materials move by simple diffusion from high concentration on one side of the membrane to a lower concentration on the other side. Water is the most abundant and one of the most important substances in cells. The diffusion of water across a membrane is called osmosis. Water will diffuse from a solution of low solute concentration to a region of high solute concentration. As the temperature of the solution increases the rate of osmosis is likely to increase by increasing the kinetic activity of the solution, the molecules within the solution will be moving around faster therefore are more likely to pass through the pores in the membrane.

Variables

Independent Variable: Temperature of NaCl solution
Dependent Variable: Change in mass of potato cube
Controlled Variables:
Time observed
Size of cube
Quantity of NaCl solution
Concentration of NaCl solution
Materials and Method

Materials
Thermometer x3
Potato Cube 2cm3 x3
Ice
250mL Beaker x3
300mL 10% NaCl solution
Paper towel
Knife
Potato Peeler
Stopwatch
Ruler
Bunsen Burner
Electronic Scales
Method
Peel the potatoes and use a ruler to measure and a knife to cut three 2x2x2cm cubes and use scale to determine the mass of the cubes. Place each cube in a separate beaker and label the beakers as 0°C, Room temperature and 70°C. Cool down 100mL of NaCl to 0°C by making an ice bath.

Heat 100mL of NaCl to 70°C with a Bunsen burner
Pour each temperature solution in the appropriately labelled beaker, ensuring to use ice to maintain the 0°C solution and a Bunsen burner to maintain the 70°C solution. Leave the cubes for 10 minutes, remove excess water and weigh and record the mass again. Calculate the change in mass and calculate % loss or gain and enter into table, also record any other observations.

Results

Table 1: Effects of temperature on rate of osmosis

Size of Cube
Temperature
Initial Mass (g)
Salt Concentration
Final Mass (g)
Change in Mass (g)
% Mass Change
2cm3
0°C
8.49
10% NaCl
8.2
- 0.29
- 3.4
2cm3
20°C
8.33
10% NaCl
8.2
- 0.13
- 1.66
2cm3
70°C
8.85
10% NaCl
8.4
- 0.45
- 5.08

Graph 1: Effects of temperature on rate of osmosis in potato cubes

As seen in Table 1 and Graph 1 the potato cube in the 70°C NaCl solution lost the...
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