In this investigation the main aim is to find out how many grams of salt (sodium chloride NaCl) Mr Chips should add per litre of water to make an isotonic solution to put his chips in were they will not gain or lose water weight through osmosis.

Mr Chips

Tracy Pearce

Introduction

Osmosis is the movement of water through the semi permeable membrane which the cells in the potato chips have. When a hypertonic solution is used and the concentration of the solution is higher than that of the potato cells the water in the potato cells passes out through the semi permeable membrane, the membrane then pulls away from the cell wall as the cells vacuole loses water, the cell then becomes plasmolysed and a weight loss occurs. When a hypotonic solution is used and the concentration of the solution is lower than that of the potato cell, water passes in through the semi permeable membrane as the vacuole fills with water and pushes the cells cytoplasm against the cell wall, the cell wall then stretches and the cell then becomes turgid and a weight gain occurs. 1

The main aim is to find an isotonic solution were the concentration of the salt in the water is the same as that in the potato chip, and then there would be neither a weight loss nor gain and the potato cells would remain flaccid. This then would be the perfect solution Mr Chips should use.

Variables

In this investigation these are the variables that will be controlled

Length of the potato cylinder
Size of the chip
Temperature
Volume of water
Time (45mins)
Different concentrations of salt
Use the same balance each time

The only thing that will change will be the weight of the potato chips at the end of the investigation.

Hypothesis

In this investigation it is predicted that the mass of the chips submerged in the 5 salt solutions will decrease because the water will move from a high to low area of concentration, so when weighed at the end they will have lost weight in grams.

For the potato chips in the 0% salt solution (distilled water) the mass will increase as the water moves the opposite way from a low to high concentration into the potato chips, this will be the only solution when weighed they will have ...

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Hypothesis

After drawing the graphs, the recorded results will be analysed and the investigation will be concluded and evaluated.

Apparatus

6 test tubes
2 test tube racks
12 labels
Distilled water
0.5% salt solution
1.0% salt solution
1.5% salt solution
2.0% salt solution
2.5% salt solution
Measuring boat
Razor blade
Cork borer
White tile (to cut chips on)
Balance
Blotting paper

Method

6 beakers were used.
100ml of water was put in each beaker.
0.5g of salt was put in the 1st beaker, 1.0g in the 2nd, 1,5g in the 3rd, 2.0g in the 4th, 2.5g in the 5th and plain distilled water in 6th beaker.
A measuring cylinder was used.
20mls of each solution was placed in 6 separate test tubes.
The test tubes were labelled accordingly.
The test tubes were placed in a test tube rack.
A cork borer was used to carefully remove 2 cylinders from the potato.
The cylinders were placed on a white tile and the ends were carefully cut off with a razor blade and discarded.
Each cylinder was cut into 9 chips 18 n total all roughly the same size.
The tile was labelled the same way as the test tubes and 3 chips were placed in front of the according label.
The chips were taken to the balance to be weighed individually.
The balance was turned on and zeroed.
The weighing boat was placed on ad the balance was zeroed again.
Each chip was placed on and weighed individually.
The weight was recorded in the column before part of table beside the name of the test tube the chips would be put in.
All the chips were placed back on the tile in front of the according labels.
Three chips were placed in each of the 6 test tubes.
The timer was set for a maximum of 45 minutes.
During the 45 minutes the cork borer and the razor blade were washed carefully and put away, as they will not be used again.
After 45minutes the water was drained from each of the 6 test tubes.
The 3 chips from each test tube were placed on a piece of blotting paper to soak up access water, in front of the according labels on the tile.
The chips were taking to the balance again to be weighed individually.
The balance was zeroed.
The weighing boat was placed on the balance and it was zeroed again.
Each chip was placed on the balance and weighed.
The balance was zeroed before each new chip was put on.
The weights were recorded again in the table this time in the column with after at the top, beside the name of the test tube the chips would be put in.
When the recordings were taken down correctly, the apparatus was washed and put away.
The chips were them discarded in the bin.

(For health and safety reasons take extra care while using the cork borer and the razor blade.)

Discussion based on results

The tables presented clearly show that the chips submerged in distilled water had a gain in weight and the chips that were submerged in the salt solutions each had an increasing weight loss.

The graphs presented for the average weight gain in percentage and grams both have a line of best fit which passes through most of the weights recorded on the graphs.

The point that the line of best fit passes through the X axis of the graph is where the isotonic point is found in this investigation on both graphs the isotonic point is 0.5g of salt per 100ml of water.

Conclusion

Now the investigation has been carried out and all the weights have been recorded and plotted on two separate graphs, it is very clear to see that the amount of salt Mr Chips should use is 0.5g per 100ml of water to make a perfect isotonic solution were the balance of salt in the solution is the same as that in the chips. Then osmosis will not occur and there will be no weight gain or loss.

5g of sodium chloride (NaCl) should be used per 1 litre of water. This was worked out by using the result gained of 0.5g of salt at the isotonic point and multiplying it by 10 as there is 1000ml in 1 litre.

Evaluation

The Investigation was carried out fairly successfully as the results appear precise and therefore fairly accurate.

A wide range of results were recorded throughout the investigation which would mean that a sufficient amount of data was created to make an informed conclusion, which complimented the predictions for the outcome of the investigation.

The investigation went well as the results were precise. The results follow a set pattern or trend which supports the idea that the conclusion made is reliable.

Investigations for each concentration could have possibly been carried out more than 3 times to ensure a better range of results. However, if the investigation was to be repeated, a larger range of sodium chloride solutions could be used to create more varied results and ensure that the isotonic point is pinpointed more accurately.

The amount of results collected is enough to make a supported conclusion as they show a clear pattern/trend and are reliable as they have very small error bars and were tested 3 times to ensure accuracy of results.

Not many problems were faced when carrying out the investigation over the 45minute time scale.

Although there were no notable issues, the method used could have created possible problems and tarnished the accuracy of the results. For example, some results were not as close to the line of best fit as others-this could have been due to human error as the potato chips were cut approximately the same size by hand. They could have been measured individually with a mm rule to make the investigation more precise. Solutions could have been measured out more accurately using a new measuring cylinder each time. This would insure that there was no cross contamination of the solutions with each other. Also each chip could have been weighed more accurately to the nearest 0.001g instead of 0.01g. Each chip could also have been dried in the same manner for the same length of time to ensure accuracy.

Overall the investigation was fairly accurate as the results are supported by the conclusion and are reliable and precise. The investigation could have been improved with changes to the method, and the conclusion could have been made more certain with improvements to the line of best fit and the way the graph was plotted. A smaller scale could have been used to plot the graph, thereby making the difference within error bars easier to read and a conclusion easier to deduce.

References