Topics: Titration, Water, Chemistry Pages: 5 (1400 words) Published: March 28, 2012
Salt from green beans

Name: Ashni Couprie and Dennise Susanto
Class: 5c

From previous experiments we've learned that salt is extracted from green beans. To be more specific: salt is extracted from when the beans are cooked in water in which salt has been dissolved. This experiment is based upon the osmoses theory. According to this theory the cell walls of the green beans are what we call a semi permeable membrane. This membrane only lets water through and not the substance that is dissolved into the water, as in this case is NaCl. Because the concentration of the salt inside the cell and in the water is different equalization will occur. You can expect that the cells will take more water inside during this experiment, so the concentration of salt in the water changes because there is the same amount of salt in less water. You could ask why the beans are being cooked in water which contains salt, when the beans themselves already contain salt. In this way we've came to the following inquiry question on which this experiment has been based.

Inquiry Question: What is the relation between the amount of salt extracted from the green beans, when they are being cooked, and the amount of mol NaCl dissolved in this water?

Hypothesis: We expect them to be dependent from each other. If more salt is dissolved in the water the cell will have take in less water. If less salt is dissolved in the water the cells will have to take in more water, so the concentration will vary much more.

The concentration of salt in the water will have to be measured in this experiment. We will do this by titration. For this we will use a pipette, a burette and an Erlenmeyer. Before we can use these we have to clean them first by rinsing them three times with the same liquid. The burette will have to be read very precisely so all the drops in the top of the burette will be wiped off.

Experimental design
* burette (50mL)
* pipette (10mL)
* dropper tube (indicator)
* cooking stones
* burner
* lighter
* tripod
* wire mesh
* large beaker (500mL)
* small beaker (50mL)
* Erlenmeyer (250mL)
* weighing machine (2 decimals)
* kitchen foil
* cutting board
* knife
* thermometer
* stopwatch
* stirring rod

* Distilled water
* NaCl-solution 0,100 M NaCl
* AgNO3 0,05 M/L
* KCrO4
* green beans

There is a standard solution of 0,100M NaCl with which the experiment begins. Starting here this solution will be thinned. We begin with adding 20 ml distilled water and extracting 20ml from the standard solution. In this way the total amount will stay the same (250 ml). The solutions vary between 250ml 0,100M NaCl and 0ml distilled water and 150ml 0,100M NaCl en 100ml distilled water. The beans will be cut into pieces of 1cm. Weighing them gives an amount of 25.09 grams. Each time a solution of exactly 250ml will be used. The solution will be heated in beaker that has been closed with kitchen foil. If a temperature of 80 degrees is reached because of heating the water, the beans that has been weighed will be put in that beaker and will be closed again. This will be heated 5 minutes. The heating occurs by placing a blue not-rustling flame under the beaker. After 5 minutes heating, the liquid will be poured into a Erlenmeyer. In this way the various solutions will be made that furthermore will be examined. Then 10,00ml of the solution from the Erlenmeyer will be pipetted and what remains can be thrown away. In this NaCl solution with unknown concentration 10 drops of the indicator KCrO4 will be added. The burette will be filled with AgNO3. The start and end values will be read out so the amount AgNO3 used is known. If the solution in the Erlenmeyer that was yellow, has turned red, the titration is completed. Results

Table 1: Measurements processed.
Starting value burette(ml)| End value burette(ml)| Amount AgNO3...
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