Kitchen Chemistry 29.10.11 by Elina Näsäkkälä [email protected] What is the importance of the topic? Students often do not understand what is the use of the chemistry knowledge in their everyday life. Kitchen chemistry hopefully increases their understanding, chemistry is a part of their everyday life. Reasons for chosing my subtopics: C-vitamin determination - teaches how go about the chemical analysis Enzymes from lettuce leaves - allows the high level theory teaching Make your own ice cream - students get the chance to practise their creativity Sensory test: Can you tell the difference between natural vanilla or ethylvanillin? VANILLA TEA SAMPLE 1 FORSMAN TEA 2 TWININGS TEA STRENGTH OF VANILLA AROMA MOST PLEASING AROMA WHICH ONE (OR BOTH) IS/ARE IN WHICH C- vitamin determination The method: DCPIP(dichlorophenol-indophenol) is a redox dye DCPIP (blue) + H+ → DCPIPH (pink) DCPIPH (pink) + VitC→ DCPIPH2 (colorless) C6H8O6 + C12H7NCl2O2 → C6H6O6 + C12H9NCl2O2 The oxidation of L-ascorbate (C-vitamin) + 2H+ + 2e- hands on - prepare a tablet solution (the best colour intensity will be, when you dissolve 2 tablets into 100 ml of water; 0,5 mg/25 ml; 1 tablet /50 ml) - prepare sample solutions (cut piece of yellow bell pepper of about 10 g and record mass accurately; chop up piece in to about 1 cm3 pieces and, in a plastic container, add 10-20 cm3 of 0,1 M ethanoic acid, use hand blender to blend the mixture, eliminating as many solid pieces as possible), - titrate by a burette or by Finnpipettes - analyze the result (fresh yellow bell pepper contains approximately 180 mg/100 g) Enzyme research 1. extract the enzyme catalase from lettuce leaves(chop up them in a plastic container and add half of the volume of the juice water 2. sett up the experiment 3. perform the experiment 4. plot the graph 5. find the Ea activation energy One set of experimental results Time(s) V(O2)/ml, V(O2)/ml, V(O2)/ml, V(O2)/ml, when T = 293 K when T = 303 K when T = 313 K when T = 323K 10 4 5 5 10 15 4 5 8 10 20 8 10 10 20 25 8 12 17 22 30 10 15 20 25 60 Finding the Ea rate = k∙[H2O2]x , where k = A∙e-Ea/RT rate = A∙e-Ea/RT ∙[H2O2]x rateinitial = A∙e-Ea/RT ∙c, where c is constant in all different temperatures ln rateinitial = lnA- Ea/RT + ln c ln rateinitial = lnA- Ea/R∙1/T Plotting the graph 0 4 8 10 0 5 10 15 0 8 10 20 0 10 20 25 30 25 20 Series1 Series2 15 Series3 Series4 10 5 0 1 2 3 4 Calculations 1. 2. 3. 4. rate inital = 10/30 rate inital = 15/30 rate inital = 20/30 rate inital = 25/30 ml/s; 1/T = 0.00341 K-1 ml/s ; 1/T = 0.00330 K-1 ml/s ; 1/T = 0.00319 K-1 ml/s ; 1/T = 0.00310 K-1 Plotting a graph again 0,0031 0,00319 0,0033 0,00341 -0,186 -0,416 -0,693 -1,109 0,2 0 1 2 3 4 -0,2 -0,4 Series1 -0,6 Series2 -0,8 -1 -1,2 Activation energy Ea Ea/R = 0,923/ 0,00031K-1 Ea =R∙0,923/ 0,00031 K-1= 24742 J/ mol ≈ 25 kJ/mol Compare, the Ea without the catalyst is 75 kJ/mol Make your own ice cream What to do 1. 2. 3. 4. Put 2 cups of crushed ice and ¼ cup of rock salt into the quart-size zipclose bag. Pour the milk(1/4 cup), heavy cream(1/4 cup), sugar (2 table spoon)and vanilla(1/2 table spoon) into the sandwich-size bag. Seal this bag tightly. Place the smaller bag inside the larger bag. Gently squeeze out the air and seal it carefully. Continue squeezing it gently for about 5 minutes. What is happening inside the bag? Drain the water from the larger bag, and add the remaining ice and salt. Seal and squeeze until mixture is very thick. Remove the small bag from the ice and dry the outside of the bag. With scissors, cut a bottom corner off the small bag and squeeze the contents into small bowls. Enjoy!