Kitchen Chemistry
29.10.11
by Elina Näsäkkälä
elina.nasakkala@syk.fi
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!