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10th May 2020

Pg#2

E2: Optimising the photochemical reaction behind blueprints In this investigation, a solution of the [Fe(C2O4)3]3– ion will made and you will optimise its photochemical conversion in the same manner for blueprints. In addition, time taken for reaction and what intensity/wavelength of light is optimal will be investigated. The formation of Prussian Blue helps determine whether photoreaction has occurred. This is will be considered in the analysis of blue prints.

Section 2.3.1: Preparation of [Fe(C2O4)3]3– stock solution and making photosensitive paper a) Stock solution: Equal portions of oxalic acid and of Fe(NO3)3·9H2O are mixed in a beaker Mix them together in a beaker. Then solutes are dissolved in approximately 10 mL of deionised water. Make sure to rinse with the water to get an remaining solute on sides. b) Photosensitive paper: Use tongs to dip the filter paper in stock solution made. Use paper towel to blot dry the filter papers. c) Pour 100 mL of deionised water a) Both b) and c) is then placed inside locker with doors shut Note: never transfer chemicals while beaker or container is on balance  prevent further contamination

Section 2.3.2 Experimental setup of irradiating [Fe(C2O4)3]3– with light 20 ml of K3 {Fe( CH )6 } is collected to test intensity of colour of solution. Stock solution is poured into all test tubes (leave one in cupboard as a control). Place all tubes under light lamp (which is clamped using a retort stand). Every minute, a test tube in ascending order, is taken to put back inside cupboard. 1ml of K3 { Fe( CH )6 } is dropped into each of the test tubes including the control. Note: Minimise errors by carrying out experiment in Figure 1: Photochemical reaction conducted cupboard from beginning Section 2.3.3 What time is required for completion of the photochemical reaction? Take all test tubes out of cupboard add drops to 4 test tubes ( 1 min to 4 min) Control: Nothing added in order for comparison to 1 min tube Table 1: Irradiation times and state of photoreduction based on intensity of final colour observed Irradiation Time ( min) Observation 0 Yellow ( hasn’t been irradiated – control ) 1 Greenish Yellow 2 Pale green 3 Green 4 Dark green Conclusion: Test tubes directly under light (dark green) . Hence 4 minutes needed for completion of photochemical reaction (irradiation)

Section 2.3.4 : What is the optimum light intensity for the photochemical reaction?

10th May 2020

Pg#2

Fill two test tubes with [Fe(C2O4)3]3– stock solution. Test tubes placed in a beaker 20 cm and 60cm away from the lamp. After 4 minutes, pour dropwise of K3 { Fe( CH )6 } into each test tube. Table 2: Distance from light source and state of photoreduction based on colour intensity Distance ( cm ) Colour intensity 20 Darker green 60 Highlight green Conclusion: Closest to light source ( 20cm )  most intense reaction  optimal light intensity

Section 2.3.5 What is the optimum light wavelength for the photochemical reaction? Filter paper is labelled in quarters ( Red, green, blue and white ) using the coloured slide as a guide. Using tongs, the filter paper is dipped into the ferrioxalate solution inside the cupboard and blot dry with paper towel. The coloured slide is placed over filter paper under the light lamp and will only allow light of a certain wavelength to pass through. Four mins later, the filter paper is dipped into K3 { Fe( CH )6 } solution Table 3: Different Wavelength and state of photoreduction based on intensity colour Section of square Colour intensity Red None Green None Blue High White High Conclusion: Green and red: Not energetic enough. Hence need blue light or higher i.e white for , photoreduction reaction to occur Note: Only corresponding colour wavelength can go through ( red light to go through red square). Every reaction requires specific activation energy ( Ae), hence different colours have different Ae. The Ae determines whether or not a reaction occurs.

2.3.6 Testing your optimal conditions Photosensitive paper made at the beginning is taken out from the cabinet, where no light was involved. Flat opaque objects like a 5 cent is placed on the paper and irradiated under the optimised conditions. Four minutes later, the paper is then dipped into a 400 mL beaker containing K3[Fe(CN)6] solution. Blue print has been developed and left on paper towel to dry. Note: dipping in deionised water can give a better resolution of blueprint Blue light White light Result: 2.4 Assessment Optimal conditions for this photochemical reaction? (1) Time needed: 4 mins (2) High intensity of blue and white colour (3) Distance: 20cm from light source ( closer the distance, higher the colour intensity Major error sources: In 2.2.2 the rest of the lights are in the lab , which affects results, as photochemical reaction can be happening under ambient light. In 2.3.3, the tubes should put in beaker before light turned, put the solution and then start timer....