Chemistry in the kitchen

Sheila Grace Tan
Sheila Grace TanUP Chinese Student Association
GROUP 9
Chemistry
  in the
 Kitchen
Red Cabbage Indicator
Materials
 Red cabbage
 Boiling water
 Chopping board
 Knife
 Strainer
 Glass bottle
 Small glasses
Materials
 Lemon
 Ascorbic acid
 Vinegar
 Apple
 Wine
 Tomato
 Cream of tartar
Materials
 Baking soda
 Household Ammonia
 Lye
Procedure

1. Chop the red cabbage
into small parts
Procedure
2. Pour some boiled water over it or boil
  it.
Procedure
3. After boiling, strain it or pour them on
  a filter paper to remove the solid
  particles.
Procedure
4. Now you have the final product. Start
  testing the pH of different solutions
  around you 
Explanation
 Red cabbage juice belongs to the
  anthocyanin family of chemicals
 Red cabbage contains a pigment
  called flavin.
 This pigment contains the natural pH
  indicator in red cabbage.
pH indicators
   pH indicators are chemicals that
    change color when an acid or base is
    added to it
pH
 The name pH means “the potential of
  hydrogen”.
 It refers to the ability of a chemical to
  donate or accept hydrogen ions from
  other chemicals
pH
 pH is a measure of how acidic or basic
  a solution is.
 The pH scale ranges from 1 to 14.
 The pH 7 is neutral.
pH
   The color of the juice changes
    because of its hydrogen ion
    concentration.

   To compute the pH of a
    solution/chemical –log[H+]
Acids
   Acid comes from the Latin word
    “acidus” meaning sour because acids
    generally have a sour taste.

   Acids donate hydrogen ions in an
    aqueous solution thus increasing the
    hydrogen ions in the solution which
    gives a low pH (less than 7).
Bases

   Bases generally have a bitter taste and a
    slimy or soapy feel to the skin.

   Bases increase the concentration of
    hydroxide ions [OH-] which decreases the
    [H+] in the solution hence giving a high pH.
Chemistry in the kitchen
pH of some common
        substances
   1.0 Battery Acid (sulfuric      5.8-6.4 peas
    acid)                           6.4 cow's milk
   1.8-2.0 limes                   6.5-7.5 human saliva
   2.2-2.4 lemon juice             7.0 distilled water
   2.2 vinegar (acetic acid)       7.3-7.5 human blood
   2.9-3.3 apple juice, cola       8.3 baking soda
   3.7 orange juice                9.2 borax
   4.0-4.5 tomatoes                11.0 laundry ammonia
   5.6 unpolluted rain             12.0 lime water
Chemistry in the kitchen
Invisible Ink
 An invisible inkis any substance that can be
  used for writing, which is not visible to the naked
  eye.
 The process of rendering the ink visible usually
  requires either heat or a pH indicator.
 Solutions of iron, silver or copper salts were used
  as ink.
 It has been used for espionage, most notably by
  the British and American armies during the
  Revolutionary War.
    ◦ The secret writing was placed between the lines of an
      innocent letter, in case they were intercepted by the
      enemy army.
    ◦ They would mark their letters written in invisible ink
      with “F” for fire and “A” for acid.
Materials Needed


           Lemon extract
           Paper
           Heat source (Candle, ligh
           Cotton Buds
Procedure
   Squeeze lemons on a bowl then add a few drops of
    water.
   Use the juice as ink, then write your message by
    using a cotton bud.
   Let it dry.
   To reveal the secret message, heat the paper by
    using a candle, lamp, or ironing it.
Chemistry Behind It
 Lemon juice is a weak organic acid
 The juice contains 5-6% citric acid
  (C6H8O7)
 When heated, the carbon compound
  breaks down, which then produces a
  black/brown color.
 The compound reacts with
  air, undergoing oxidation.
 Another explanation is that the acid
  weakens the paper fibers, which causes
  the weak parts to burn first.

                  CITRIC ACID
Citric Acid
  Citric acid is a natural acid that is
  commonly found in a variety of fruits.
 Other uses of citric acid:
    ◦ Food additive and preservative
    ◦ Cleaning agent
    ◦ Widely used in cosmetics
   Other citrus fruits such as orange
    and lime contain high concentration
    of citric acid, so they can also be
    used as invisible inks.
Water – Wine – Milk – Beer

Unit on Acids, Bases and Salts
Materials
 2 ordinary drinking glasses
 1 wine glass
 1 beer mug
 Water
 25 mL saturated sodium bicarbonate
  solution 20% sodium carbonate solution
  (pH = 9)
 phenolphthalein indicator
 10 mL saturated barium chloride solution
 sodium dichromate crystals
 5 mL concentrated hydrochloric acid
Chemistry in the kitchen
A basic solution of sodium bicarbonate
(NaHCO3), which is baking soda, and
sodium carbonate (Na2CO3), which is
soda ash is prepared. These
substances are water-soluble resulting
in a clear solution with an appearance
the same as plain water. The pH of the
solution is about pH = 9 (basic)
whereas the pH of plain water is about
pH=7.
The wine glass contains a few drops of
phenolphthalein indicator. This is a
liquid that turns pink in basic solutions.
Larger quantities of phenolphthalein in
solution will produce a darker color;
therefore the solution appears to be
wine.
The milk glass contains a small
quantity of saturated barium chloride
solution. With the addition of excess
base to this saturated solution, the
barium chloride will precipitate the
carbonate ions from the solution
forming barium carbonate
(BaCO3), which is insoluble in water.
The precipitate disperses throughout
the glass as a white solid and gives the
appearance of milk.
The beer glass contains about 5mL
acid (HCl, which is a strong acid) and
a few crystals of sodium dichromate
(Na2Cr2O7). The BaCO3 from the milk
glass is soluble in acidic solutions
(pH 4) so the solids re-dissolve in the
acidic solution to form a clear liquid.
However, Na2Cr2O7 dissolves to give a
pale orange color, which resembles the
appearance of a mug of beer.
Disappearing Ink
Materials
 125 mL Erlenmeyer flask
 rubber stopper
 50 mL ethyl alcohol
 less than 1 mL of thymolphthalein indictor
 less than 1 mL of 0.1 M sodium hydroxide
 dropper
 white cotton shirt
   Pour 50 mL of the ethyl alcohol in the 125 mL
    flask.
   Add 2-3 droppers full of thymolphthalein indicator
    to the ethyl alcohol.
   Add just enough sodium hydroxide (about 2 drops)
    so a dark blue color is created. Some adjustments
    may be needed on the amount of sodium
    hydroxide to add.
   Place the rubber stopper in the flask while the
    solution is being stored.
   Fill the dropper with some of the blue indicator
    solution.
   Squirt the solution onto the white cotton shirt and
    in a few seconds the blue "stain" will disappear.
    (The residue comes off in the wash. This does not
    seem to work well with paper).
The sodium hydroxide causes the indicator of
thymolphthalein solution to turn the dark blue
color. When the solution is squirted onto the
shirt, it reacts with the carbon dioxide in the air.
The carbon dioxides reacts with the water to
form an acid called carbonic acid. The carbonic
acid then reacts with the sodium hydroxide in a
neutralization reaction. This reaction forms
sodium carbonate, which is a washing
soda, and the stain disappears. The carbon
dioxide is the acid that neutralizes the
base, sodium hydroxide. The color of the
thymolphthalein is colorless in the presence of
acid.
Ice Cream in a Bag
What you'll need:
1 tablespoon sugar
1/2 cup milk or half & half
1/4 teaspoon vanilla
6 tablespoons rock salt
1 pint-size plastic food storage bag (e.g., Ziploc)
1 gallon-size plastic food storage bag
Ice cubes
How to make it:
Fill the large bag half full of ice, and add the rock salt. Seal the bag.
Put milk, vanilla, and sugar into the small bag, and seal it.
Place the small bag inside the large one, and seal it again carefully.
Shake until the mixture is ice cream, which takes about 5 minutes.
Wipe off the top of the small bag, then open it carefully. Enjoy!
Tips:
A 1/2 cup milk will make about 1 scoop of ice cream, so double the recipe if you
want more.
Why does salt do?
   Adding salt to the ice lowers the
    freezing point of the ice, so even more
    energy has to be absorbed from the
    environment in order for the ice to
    melt. This makes the ice colder than it
    was before, which is how the ice
    cream freezes. The larger crystals of
    the rock salt take more time to
    dissolve in the water around the
    ice, which allows for even cooling of
    the ice cream.
Why salt?
 You could use other types of salt instead of sodium
  chloride, but you couldn't substitute sugar for the salt because
  (a) sugar doesn't dissolve well in cold water and (b) sugar
  doesn't dissolve into multiple particles, like an ionic material
  such as salt.
 Compounds that break into two pieces upon dissolving, like
  NaCl breaks into Na+ and Cl-, are better at lowering the
  freezing point than substances that don't separate into
  particles because the added particles disrupt the ability of the
  water to form crystalline ice. The more particles there are, the
  greater the disruption and the greater the impact on particle-
  dependent properties like freezing point depresssion, boiling
  point elevation, and osmotic pressure. To make ice cream the
  cream mixture needs to change from a liquid to a solid. This
  process is called freezing (a phase change) and requires heat
  to be removed from the mixture. The addition of salt to the ice
  is needed for the phase change to take place. This is
  because salt lowers the melting point of ice and in this
  process requires heat from the surroundings (endothermic
  change). The melting ice lose its heat energy and thus
  freezes the ice cream.
Chemistry in the kitchen
In order to generate electricity, there must be a power
source and a complete circuit. When using a citrus fruit to
create electricity, these rules still apply. In a simple
experiment using a citrus fruit, the components of the circuit
include: a lemon or other fruit, wire, two different metal
element. The lemon in this circuit serves as the battery and
power source.
Two metals often used in this demonstration are zinc and
copper. The acidic juice of the lemon dissolves small
amounts of the two metals and their electrons react with
each other. The negatively charged ions travel through the
wires, creating an electrical current. (Electricity is the
movement of electrons.) This demonstration is a closed
circuit, which allows electrons to flow from the power source
and back again, with no breaks.
The lemon, with the zinc and copper, becomes a battery. A
battery is composed of two metals and an electrolyte. An
electrolyte is a conductive liquid; here, the lemon juice
performs this function. A chemical reaction takes place
between the metals within the citrus fruit. This creates
voltage, which pushes the electrons through the circuit.
A common misunderstanding is that citrus fruits create
electricity. What happens is the electrolyte (the citrus juice)
Fruit Charger
 Lemon juice is highly concentrated with citic acid, which
  gives the fruit a bitter taste, but also makes it a great
  conductor of electricity.
 When acids are dissolved into water, the acids break
  apart into positive and negatively charged ions. These
  ions have the power to conduct electricity through a
  liquid like lemon juice.
 Through a process known as oxidation-reduction, the
  citric acid in the lemon juice and the metals pushed into
  the flesh of the lemon will form a reaction which results
  in an electric current. One metal will lose its electrons, a
  process known as oxidation, and other metal gains
  those lost electrons, a process known as reduction.
 Because the citiric acid in the lemons is so highly
  concentrated, all it takes is a few pieces of metal to
  yield an electric output much like that of a battery's
  electric current.
Sources
   http://artins.org/ben/misc/invisible-inks.pdf
   http://www.sciencekids.co.nz/experiments/invi
    sibleink.html
   http://www.scienceoutsidethebox.com/More%
    20Fun%20With%20Science_files/JCE1006p1
    479-1483.pdf
   http://chemistry.about.com/cs/howtos/ht/invisi
    bleink3.htm
   http://www2.si.umich.edu/spies/methods-
    ink.html
   http://science.kqed.org/quest/2012/03/07/try-
    this-at-home-invisible-ink/
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Chemistry in the kitchen

  • 2. Chemistry in the Kitchen
  • 4. Materials  Red cabbage  Boiling water  Chopping board  Knife  Strainer  Glass bottle  Small glasses
  • 5. Materials  Lemon  Ascorbic acid  Vinegar  Apple  Wine  Tomato  Cream of tartar
  • 6. Materials  Baking soda  Household Ammonia  Lye
  • 7. Procedure 1. Chop the red cabbage into small parts
  • 8. Procedure 2. Pour some boiled water over it or boil it.
  • 9. Procedure 3. After boiling, strain it or pour them on a filter paper to remove the solid particles.
  • 10. Procedure 4. Now you have the final product. Start testing the pH of different solutions around you 
  • 11. Explanation  Red cabbage juice belongs to the anthocyanin family of chemicals  Red cabbage contains a pigment called flavin.  This pigment contains the natural pH indicator in red cabbage.
  • 12. pH indicators  pH indicators are chemicals that change color when an acid or base is added to it
  • 13. pH  The name pH means “the potential of hydrogen”.  It refers to the ability of a chemical to donate or accept hydrogen ions from other chemicals
  • 14. pH  pH is a measure of how acidic or basic a solution is.  The pH scale ranges from 1 to 14.  The pH 7 is neutral.
  • 15. pH  The color of the juice changes because of its hydrogen ion concentration.  To compute the pH of a solution/chemical –log[H+]
  • 16. Acids  Acid comes from the Latin word “acidus” meaning sour because acids generally have a sour taste.  Acids donate hydrogen ions in an aqueous solution thus increasing the hydrogen ions in the solution which gives a low pH (less than 7).
  • 17. Bases  Bases generally have a bitter taste and a slimy or soapy feel to the skin.  Bases increase the concentration of hydroxide ions [OH-] which decreases the [H+] in the solution hence giving a high pH.
  • 19. pH of some common substances  1.0 Battery Acid (sulfuric  5.8-6.4 peas acid)  6.4 cow's milk  1.8-2.0 limes  6.5-7.5 human saliva  2.2-2.4 lemon juice  7.0 distilled water  2.2 vinegar (acetic acid)  7.3-7.5 human blood  2.9-3.3 apple juice, cola  8.3 baking soda  3.7 orange juice  9.2 borax  4.0-4.5 tomatoes  11.0 laundry ammonia  5.6 unpolluted rain  12.0 lime water
  • 21. Invisible Ink  An invisible inkis any substance that can be used for writing, which is not visible to the naked eye.  The process of rendering the ink visible usually requires either heat or a pH indicator.  Solutions of iron, silver or copper salts were used as ink.  It has been used for espionage, most notably by the British and American armies during the Revolutionary War. ◦ The secret writing was placed between the lines of an innocent letter, in case they were intercepted by the enemy army. ◦ They would mark their letters written in invisible ink with “F” for fire and “A” for acid.
  • 22. Materials Needed  Lemon extract  Paper  Heat source (Candle, ligh  Cotton Buds
  • 23. Procedure  Squeeze lemons on a bowl then add a few drops of water.  Use the juice as ink, then write your message by using a cotton bud.  Let it dry.  To reveal the secret message, heat the paper by using a candle, lamp, or ironing it.
  • 24. Chemistry Behind It  Lemon juice is a weak organic acid  The juice contains 5-6% citric acid (C6H8O7)  When heated, the carbon compound breaks down, which then produces a black/brown color.  The compound reacts with air, undergoing oxidation.  Another explanation is that the acid weakens the paper fibers, which causes the weak parts to burn first. CITRIC ACID
  • 25. Citric Acid  Citric acid is a natural acid that is commonly found in a variety of fruits.  Other uses of citric acid: ◦ Food additive and preservative ◦ Cleaning agent ◦ Widely used in cosmetics  Other citrus fruits such as orange and lime contain high concentration of citric acid, so they can also be used as invisible inks.
  • 26. Water – Wine – Milk – Beer Unit on Acids, Bases and Salts
  • 27. Materials  2 ordinary drinking glasses  1 wine glass  1 beer mug  Water  25 mL saturated sodium bicarbonate solution 20% sodium carbonate solution (pH = 9)  phenolphthalein indicator  10 mL saturated barium chloride solution  sodium dichromate crystals  5 mL concentrated hydrochloric acid
  • 29. A basic solution of sodium bicarbonate (NaHCO3), which is baking soda, and sodium carbonate (Na2CO3), which is soda ash is prepared. These substances are water-soluble resulting in a clear solution with an appearance the same as plain water. The pH of the solution is about pH = 9 (basic) whereas the pH of plain water is about pH=7.
  • 30. The wine glass contains a few drops of phenolphthalein indicator. This is a liquid that turns pink in basic solutions. Larger quantities of phenolphthalein in solution will produce a darker color; therefore the solution appears to be wine.
  • 31. The milk glass contains a small quantity of saturated barium chloride solution. With the addition of excess base to this saturated solution, the barium chloride will precipitate the carbonate ions from the solution forming barium carbonate (BaCO3), which is insoluble in water. The precipitate disperses throughout the glass as a white solid and gives the appearance of milk.
  • 32. The beer glass contains about 5mL acid (HCl, which is a strong acid) and a few crystals of sodium dichromate (Na2Cr2O7). The BaCO3 from the milk glass is soluble in acidic solutions (pH 4) so the solids re-dissolve in the acidic solution to form a clear liquid. However, Na2Cr2O7 dissolves to give a pale orange color, which resembles the appearance of a mug of beer.
  • 34. Materials  125 mL Erlenmeyer flask  rubber stopper  50 mL ethyl alcohol  less than 1 mL of thymolphthalein indictor  less than 1 mL of 0.1 M sodium hydroxide  dropper  white cotton shirt
  • 35. Pour 50 mL of the ethyl alcohol in the 125 mL flask.  Add 2-3 droppers full of thymolphthalein indicator to the ethyl alcohol.  Add just enough sodium hydroxide (about 2 drops) so a dark blue color is created. Some adjustments may be needed on the amount of sodium hydroxide to add.  Place the rubber stopper in the flask while the solution is being stored.  Fill the dropper with some of the blue indicator solution.  Squirt the solution onto the white cotton shirt and in a few seconds the blue "stain" will disappear. (The residue comes off in the wash. This does not seem to work well with paper).
  • 36. The sodium hydroxide causes the indicator of thymolphthalein solution to turn the dark blue color. When the solution is squirted onto the shirt, it reacts with the carbon dioxide in the air. The carbon dioxides reacts with the water to form an acid called carbonic acid. The carbonic acid then reacts with the sodium hydroxide in a neutralization reaction. This reaction forms sodium carbonate, which is a washing soda, and the stain disappears. The carbon dioxide is the acid that neutralizes the base, sodium hydroxide. The color of the thymolphthalein is colorless in the presence of acid.
  • 37. Ice Cream in a Bag What you'll need: 1 tablespoon sugar 1/2 cup milk or half & half 1/4 teaspoon vanilla 6 tablespoons rock salt 1 pint-size plastic food storage bag (e.g., Ziploc) 1 gallon-size plastic food storage bag Ice cubes How to make it: Fill the large bag half full of ice, and add the rock salt. Seal the bag. Put milk, vanilla, and sugar into the small bag, and seal it. Place the small bag inside the large one, and seal it again carefully. Shake until the mixture is ice cream, which takes about 5 minutes. Wipe off the top of the small bag, then open it carefully. Enjoy! Tips: A 1/2 cup milk will make about 1 scoop of ice cream, so double the recipe if you want more.
  • 38. Why does salt do?  Adding salt to the ice lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how the ice cream freezes. The larger crystals of the rock salt take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.
  • 39. Why salt?  You could use other types of salt instead of sodium chloride, but you couldn't substitute sugar for the salt because (a) sugar doesn't dissolve well in cold water and (b) sugar doesn't dissolve into multiple particles, like an ionic material such as salt.  Compounds that break into two pieces upon dissolving, like NaCl breaks into Na+ and Cl-, are better at lowering the freezing point than substances that don't separate into particles because the added particles disrupt the ability of the water to form crystalline ice. The more particles there are, the greater the disruption and the greater the impact on particle- dependent properties like freezing point depresssion, boiling point elevation, and osmotic pressure. To make ice cream the cream mixture needs to change from a liquid to a solid. This process is called freezing (a phase change) and requires heat to be removed from the mixture. The addition of salt to the ice is needed for the phase change to take place. This is because salt lowers the melting point of ice and in this process requires heat from the surroundings (endothermic change). The melting ice lose its heat energy and thus freezes the ice cream.
  • 41. In order to generate electricity, there must be a power source and a complete circuit. When using a citrus fruit to create electricity, these rules still apply. In a simple experiment using a citrus fruit, the components of the circuit include: a lemon or other fruit, wire, two different metal element. The lemon in this circuit serves as the battery and power source. Two metals often used in this demonstration are zinc and copper. The acidic juice of the lemon dissolves small amounts of the two metals and their electrons react with each other. The negatively charged ions travel through the wires, creating an electrical current. (Electricity is the movement of electrons.) This demonstration is a closed circuit, which allows electrons to flow from the power source and back again, with no breaks. The lemon, with the zinc and copper, becomes a battery. A battery is composed of two metals and an electrolyte. An electrolyte is a conductive liquid; here, the lemon juice performs this function. A chemical reaction takes place between the metals within the citrus fruit. This creates voltage, which pushes the electrons through the circuit. A common misunderstanding is that citrus fruits create electricity. What happens is the electrolyte (the citrus juice)
  • 42. Fruit Charger  Lemon juice is highly concentrated with citic acid, which gives the fruit a bitter taste, but also makes it a great conductor of electricity.  When acids are dissolved into water, the acids break apart into positive and negatively charged ions. These ions have the power to conduct electricity through a liquid like lemon juice.  Through a process known as oxidation-reduction, the citric acid in the lemon juice and the metals pushed into the flesh of the lemon will form a reaction which results in an electric current. One metal will lose its electrons, a process known as oxidation, and other metal gains those lost electrons, a process known as reduction.  Because the citiric acid in the lemons is so highly concentrated, all it takes is a few pieces of metal to yield an electric output much like that of a battery's electric current.
  • 43. Sources  http://artins.org/ben/misc/invisible-inks.pdf  http://www.sciencekids.co.nz/experiments/invi sibleink.html  http://www.scienceoutsidethebox.com/More% 20Fun%20With%20Science_files/JCE1006p1 479-1483.pdf  http://chemistry.about.com/cs/howtos/ht/invisi bleink3.htm  http://www2.si.umich.edu/spies/methods- ink.html  http://science.kqed.org/quest/2012/03/07/try- this-at-home-invisible-ink/