Chemistry in the kitchen

GROUP 9

Chemistry in the Kitchen

Red Cabbage Indicator

MaterialsRed cabbageBoiling waterChopping boardKnifeStrainerGlass bottleSmall glasses

MaterialsLemonAscorbic acidVinegarAppleWineTomatoCream of tartar

MaterialsBaking sodaHousehold AmmoniaLye

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

ExplanationRed cabbage juice belongs to the

anthocyanin family of chemicalsRed cabbage contains a pigment

called flavin.This pigment contains the natural

pH indicator in red cabbage.

pH indicatorspH indicators are chemicals that

change color when an acid or base is added to it

pHThe name pH means “the

potential of hydrogen”.It refers to the ability of a

chemical to donate or accept hydrogen ions from other chemicals

pHpH is a measure of how acidic or

basic a solution is.The pH scale ranges from 1 to

14.The pH 7 is neutral.

pHThe color of the juice changes

because of its hydrogen ion concentration.

To compute the pH of a solution/chemical –log[H+]

AcidsAcid 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.

pH of some common substances

1.0 Battery Acid (sulfuric acid)

1.8-2.0 limes 2.2-2.4 lemon juice 2.2 vinegar (acetic

acid) 2.9-3.3 apple juice,

cola 3.7 orange juice 4.0-4.5 tomatoes 5.6 unpolluted rain

5.8-6.4 peas 6.4 cow's milk 6.5-7.5 human saliva 7.0 distilled water 7.3-7.5 human blood 8.3 baking soda 9.2 borax 11.0 laundry ammonia 12.0 lime water

Invisible Ink

Using organic acids and heat

Invisible InkAn invisible ink is 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 extractPaperHeat source (Candle, light bulb,

etc.)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 ItLemon 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

Materials2 ordinary drinking glasses1 wine glass 1 beer mugWater25 mL saturated sodium bicarbonate

solution 20% sodium carbonate solution (pH = 9)

phenolphthalein indicator10 mL saturated barium chloride solutionsodium dichromate crystals5 mL concentrated hydrochloric acid

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 (pH4) 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

Materials125 mL Erlenmeyer flaskrubber stopper50 mL ethyl alcoholless than 1 mL of thymolphthalein

indictorless than 1 mL of 0.1 M sodium

hydroxidedropperwhite 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 BagWhat 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.

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) combined with the zinc and the copper form a battery, which in turn completes an electrical circuit.

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.

Sourceshttp://artins.org/ben/misc/invisible-inks.pdfhttp://www.sciencekids.co.nz/experiments/

invisibleink.htmlhttp://www.scienceoutsidethebox.com/More

%20Fun%20With%20Science_files/JCE1006p1479-1483.pdf

http://chemistry.about.com/cs/howtos/ht/invisibleink3.htm

http://www2.si.umich.edu/spies/methods-ink.html

http://science.kqed.org/quest/2012/03/07/try-this-at-home-invisible-ink/