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Osmosis Lab Case Essay Sample

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  • Pages: 5
  • Word count: 1,143
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  • Category: osmosis

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Introduction of TOPIC

Introduction

Osmosis is the movement of water molecules from an area of high concentration (low solute concentration) to an area of low concentration (high solute concentration). This passive form of transport is one that involves a semi permeable membrane. We humans and other animals contain many cells, and these cells all have a permeable membrane in which diffusion/osmosis occurs. This movement of water is vital to our lives.

Focused Problem

I will investigate how the concentration of salt in water (moles) will affect the rate of osmosis.

? This will be observed by placing a cellulose bag (or “cell”) into a beaker concentrated with salt. The rate of osmosis will be observed by first weighing the cellulose bag’s initial mass, and after the 24 hour time period, the final mass will be measured to see just how much the concentration of salt affects the rate of osmosis across the semi permeable membrane. Therefore, by finding out what concentration produces what results, we can apply this to instances where we might want to alter the rate of osmosis to benefit us.

Hypothesis

The higher the concentration of salt solution in the beaker (environment outside of the semi permeable tubing), the faster the rate of osmosis will be out of the “cell”. The lower the concentration of salt in the solution, the slower the rate of osmosis will be. This is due to the fact that the salt (solute) decreases the concentration of the water outside of the cell, which contains a 100% water (solvent). Water will go out of the higher concentration inside the cell and out to the lower concentration where the salt is.

Independent Variable

The concentration of salt it the water solution, which acts as an environment around the cellulose bag, or the “cell”. A constant amount of 500ml of distilled water is used, along with different concentrations of salt, meaning different molarities.

Dependent Variable

The rate of osmosis will be observed by weighing the initial mass of the cellulose bags, and then the “final” mass after the 24-hour period inside the beaker. This difference in mass will determine how the concentration of salt affects the rate at which osmosis takes place.

Controlled Variables

Temperature

The temperature of the water was always held at a constant of 25�C. To make sure

that the temperature would always stay the same, we kept our experiments in a cupboard where there would be little or no change in temperature. By preventing a change in temperature, we made certain that an increase/decrease in temperature would not speed up/slow down the rate of osmosis.

Time

The time span in which the cellulose bags were kept in the beakers were always at a constant time of around 24 hours. This number may not be a 100% accurate for all of our tests, but we made sure that the 24 -hour rule was kept throughout all of our tests. The slightest change in time may not have made a significant change to the rate of osmosis in this case, as osmosis is not something that happens instantly.

Volume

The volume and amount of distilled water used in our experiment was always held at a constant amount. 10ml of distilled water was placed inside all of our cellulose bags. Each beaker was filled with 500ml of distilled water. Some of our “initial mass” measurements don’t show the figure 10 grams, as there may have been some very little water loss or gain during the process of making the cellulose bags.

Cell Size

All our “cells” were cut and made at the same size. This was done to make sure that no cell would have greater surface area that may affect the rate of osmosis, and therefore make our experiment not fair.

Scale

The same electronic scale was used at all times in measuring the numerous things in our experiment. This accurate scale was used to prevent and mass differences that could make our experiment inaccurate.

Apparatus

* Cellulose Tubing

* Distilled Water

* Beakers

* Graduated Cylinder

* Electronic Scale

* Scissor

* String

* Ruler

* Salt

* Stirring Rod

Procedure

1. Gather and prepare all the items from the list of apparatus’.

2. Fill 5 beakers with 500ml of distilled water each.

3. For the first set of results (5 beakers), no salt is needed to be placed into the beaker. For the second set of results, place 25 grams of salt that you have measured on the electric scale into the beaker. Place the same amounts of salt into each beaker. Increase the amount of salt by 25 grams for each set of results. The fifth and final set of results will contain 100 grams of salt in the beaker.

4. Stir the salt with a stirring rod until the salt completely dissolves.

5. Cut out 14cm of cellulose tubing with scissors. Cut out 5 of these, one for each beaker.

6. Tie one end of the cellulose tubing, and by using the graduated cylinder, place 10ml of distilled water into the slightly wet cellulose tubing.

7. Tie the other end, and then to prevent water loss, tie a double knot at each end with pieces of string.

8. At this point, weigh the initial mass of the cell and record it using an electric scale.

9. Place the cellulose tubing into each beaker.

10. Place the 5 beakers in a cupboard, and wait 24 hours for osmosis to take place.

11. Take out the cellulose bags, dry them off a little, and then weigh their “final mass” to find out how much water was gained/lost due to osmosis.

12. Record the difference, which indicated the rate of osmosis.

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