Trace Metals

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to boiling and steaming.

Boiling would retain the least amount of ions as it is a cooking method where the food item is cooked by the direct contact of immersing in boiling water. The direct contact increases the leaching of the ions due to the breaking of the cells therefore it is the worse cooking method.

Steaming would be a better choice compared to boiling. Steaming is a method of cooking where the condensation of steam cooks the food item. Less ions would be leached as there is lesser contact with water compared to boiling which is a full immersion into water. Since water introduced is lesser in steaming, the effect of leaching is reduce and therefore it would be a better cooking method compared to boiling.

1.3 Variables

Table 1.3 : list of variables

Variables Type of variable

Cooking methods Independent

Duration of cooking independent

Concentration of Fe3+ ions Dependent

Weight of Spinach used controlled

Concentration of chemical used Controlled

Amount of water used for steaming/boiling Controlled

Time to ash spinach sample Controlled

Method of control

The weight of spinach was controlled by measuring exactly 6.000g of leaves with an electronic balance. This ensures that there is equal masss of leaves for this experiment. The concentration of chemicals are kept controlled by using new samples each time provided by the lab, it is then assume that the chemicals concentration do not change over time. Also the amount of water used for boiling is kept constant at 100cm3 measured by a volumetric flask. Lastly, time taken to ash the spinach controlled using a stop watch to time 20 min for each experiment to allow complete combustion

1.4 Assumptions

In this experiment, there are a few assumptions to be made.

-the thiocynate ions would not interfere with the results in the uv visible spectrophotometer

-all solutions used in the experiment are stable throughout the experiment and their concentrations do not fluctuate

-the spinach are bought as one batch to prevent large variations in quality and ion content in it due to climatic changes which might affect the vegetables at the country of harvest. Thus it is then assumed that all the spinach used in this experiment have the same concentration of Fe 3+ ions

-it is assumed that the ions tested in this experiment are Fe 3+ ions. There might be other ions present, such as magnesium in chlorophyll. To reduce this, the ashing method was used to combust all the chlorophyll present.

Chapter 2: Methodology

2.1 Apparatus

Table 2.1 : list of apparatus/materials required

Apparatus Quantity

20cm3 Pipette x1

50 cm3 Burette X1

250 cm3Conical Flask X4

100 cm3 Beaker X3

10 cm3Measuring cylinder X1

100/250 cm3 X1

Crucible X1

Bunsen Burner X1

Steamer Self provided

Microwave Self provided

2.0 mol/dm3 hydrochloric acid Provided by laboratory

2.2 Using UV-Visible spectrometry

2.2.1Preparations for standard solutions

Table 2.2.1 :preparation of FeCl3standard solutions

1 Make a stock of 0.001mol/dm3FeCl3 by add 0.0162g of salt into 100cm3 of Distilled water

2 Dilute stock with different amount of HCl as follow:

3 Fe3+ concentration/moldm-3 Volume of FeCl3 solution/cm3 Volume of HCl(2.0mol/dm-3)/cm3

0.00005 0.5 9.50

0.00010 1.0 9.00

0.00015 1.5 8.50

0.00020 2.0 8.00

0.00025 2.5 7.50

4 Prepare 0.15mol/dm3 of Sodium Thiocynate(NaSCN) solution by dissolving 1.2161g of salt in distilled water

5 Add 5 cm3 of this NaSCN solution into the standard solutions in boiling tubes

5 Run UV Visible spectrometry on standard solution to plot standard curve of concentration of Fe3+against absorbance, with absorbance set at