Growing crystals at home

What is a crystal?
Crystals are regular structures formed by a regular repeating pattern of atoms or molecules.

These structures grow by a process called nucleation. During nucleation, the atoms or molecules of what we want to transform in a crystal (solute) are dissolved in a solvent. The particles of the solute will tend to cluster together, forming subunits of atoms or molecules. These larger particles will also group with each other and eventually become large enough to "pop out" the solution (crystallize).

Other solute molecules will continue to adhere to the surface of the crystal, causing it to grow until equilibrium is achieved between the solute molecules in the crystal and the solution.

Growing crystals
Three factors that can influence the growth of "home" crystals:

• A good/poor solution saturation- The first stage of home crystal growth is a saturated solute. In a saturated solution the probability of molecules colliding with each other in order to form a core for initiating nucleation is greatly increased.

• Surface type-A rough surface tends to be more attractive for nucleation. It is more likely that a crystal is formed on a piece of rough rope than the in the smooth walls of a glass.

• The presence of deposits in the bottom-This occurs when the solution is not scrambled or means that too much solute was added to saturate the solution. The presence of these deposits create areas for optimum crystal growth however prevents crystal formation in the "target."

Lets see how to grow sugar crystals, these crystals can be sucked and eaten like a lollipop. This demonstration may take up to 3 weeks.


We will need:

• 3 cups of sugar, we have to adjust this quantity, we want to saturated at 100% but no precipitate,
• cup of water, to boil,
• food coloring,
• small jar,
• small bowl,
• wood stick, or rope,
• kitchen paper or paper filter.

How to:

1. Boil the water, careful with burns!;
2. In the bowl, mix the boiling water with the sugar;
3. Stir the water until all the sugar is dissolved;
4. If you want to give sugar some color, now it's the time, add the food coloring;
5. Place this solution in the jar, attention! wash the jar really well to avoid nucleation in it's walls;
6. Avoid any amount of sugar precipitate in the jar- any not dissolved sugar-, this sugar will be a good nucleation "start point";
7. Suspend the stick or rope in the solution, do not wash those, we want this to be a suitable "start up" spot for nucleation;
8. Chose a nice and quiet spot to place your jar for at least 3 weeks;
9. Wait until the solution cool and cover it with a paper filter. 

What happens?  
After cooling the solution will use nucleation spots to form crystals.

NOTE: You must check the jar on daily basis, if you see any nucleation in jar walls, change the jar;

Wait about 3 weeks for excellent results.

Go further:

• Follow the growing crystals with a graph;
• Use salt and compare the growing velocity with the sugar;
• Use 3 jars, in the first one use boiling water, in the second tepid water, and in the last one repeat the essay with cold water;
• Try to dissolve the sugar/salt/other while the water is boiling;
• I am sure you can remember other ways to change this demonstration into a experiment...

 Source: about.com; squidoo.com; buzzle.com
Et Voilá!
Science you can eat!  

Enjoy!

Geyser Cola/ Mentos or Soda/ Candy

At first looks like a dangerous and silly prank, but if well done, on the right place is spectacular, and makes all adults want to be restless young minds.

Don't do this at home, chose an easy cleaning place!

What we need:

• 1 coke bottle, full,
• 1 Mentos pack,
• 1 cardboard, enough to "close" the bottle,
• 1 test tube... or a paper funnel,

How to:

1. Chose the place to this demonstration wisely, it will be messy, and you must be able to run away... fast;
2. Uncap the coke bottle;
3. Place all the Mentos (about 10) on the paper funnel, or test tube;
4. If you are using a test tube , place the cardboard on the top and turn the tube upside down;
5. If you are using the funnel close the end with the cardboard;
6. Place the tube/funnel on the bottle uncapped top;
7. Look around and chose a direction to run away;
8. Remove the card quickly, so the candies fall in the bottle.
9. Run!

"Parents friendly" alternative
You can do this on a smaller scale, without the amazing geyser but with same effect, and best of all, without the mess.

What we need:

• 1 glass,
• 1 Mentos pack,
• Coke or other carbonated drink.

How to:

1. Put the glass inside a bowl;
2. Fill half of the glass with your drink;
3. Throw 1 Mentos inside;
4. You don't need the running part.

Results:

Before any further conclusion, 

• What happens isn't a chemical reaction! its a physical phenomenum, witch results in the sudden production of carbon dioxide resulting in a massive bubbling;
•  If we look closer, Mentos surface is very rough... those irregularities are responsible for gas formation and sudden release.
• Soda is made up mostly of water and sugar.

Knowing, these 3 things, lets try to find out what happen:

Carbonic drinks, like coke and other sodas, contain, as its name indicates, dissolved carbon dioxide. This gas is in equilibrium  and under a certain pressure- that’s the key the pressure- ready to escape as soon as the pressure on the liquid surface lower. All we know that’s necessary to remove the cap of the bottle with careful, without shake the liquid, otherwise all the drink will come out the bottle.
Until you open the bottle, the gas remains in suspension on liquid, and it can expand to form bubbles.
Note that if you place the soda in a glass and submerge a toothpick on it, its surface will form bubbles immediately.

Why?
Water molecules attracted each other strongly, holding the gas bubble in a kind of water molecules net. To form a new bubble or to expand the existing bubbles the water molecules must to move away from each other. Extra energy is needed to break this surface tension! In other words the water shows resistance to soda bubble expansion.

In this demonstration Mentos candy is going to perturb the coke equilibrium, the surface tension, this allows the CO2 to escape.

How?
When you drop the Mentos on the bottle the surface tension is disturbed, and therefore the expansion and formation of new CO2 bubbles becomes possible. Mentos have thousands of micro holes on the surface those are called nucleation places- perfect places to form CO2 bubbles. As soon as Mentos touch the soda the bubble formation is initiated in its entire surface.
When all this CO2 is released from the bottle takes the liquid with it.

In conclusion:
This process depends greatly on CO2-under pressure- and on a element that disturb the tension -the element must be porous with nucleation holes), So we can conclude this demonstration can be done with any drink with bubbles like Sprite, beer, or even Red Bull.
We don’t know any other candy that works best then Mentos. They have thousands porous and heavy; they drown and don’t come out with the geyser.



Watch MithBusters movie "MythBusters - Diet Coke & Mentos":


Note that: Internet sources tells us that the use of diet coke works best because the low sugar ratio, witch delays the bubble formation

Sources:
Mentos e Coca-Cola- Ciência Hoje



Et voilá!

Enjoy!

Vulcano- Sodium Bicarbonate and Vinager eruption

This is one of the most popular homemade experiences, not the one that give us less work but the one that has more fans with amazing results.
Don’t build your volcano indoors, chose a place where you can do a big and huge mess, with fresh air circulation, vinegar smell can become very strong.

We will need:

• baking soda- sodium bicarbonate,
• vinegar, white and without flavors will work better,
• food coloring, lava is red but you can do it any color you chose, 
• plastic bottle, PET, medium,
• 6 flour cups,
• 2 water cups,
• 4 oil tablespoons,
• 2 salt cups,
• tap water,
• dishwasher detergent,
• big bowl,
• materials like leaves, branches, sticks... ,
• large board.

How to

FASE1

1. Prepare the place where you are going to build the volcano, beware with your clothes;
2. Mix the flour, the water, the salt and the oil in the bowl;
3. Mix until homogenized;
4. Place the bottle on the board and mold the volcano cone around it. The bottleneck will be the crater and therefore must remain open;
5. With the materials you collect- leaves, branches, sticks... - place your trees, houses, bridges, etc.

FASE 2- Eruption

1. Fill the bottle in the volcano halfway with the tap water;
2. Add food coloring, and about 6 dishwasher detergent drop;
3. Add 3 or 4 tablespoons of baking soda;
4. Squeeze vinegar bottle to the crater;

NOTE: As soon as you squeeze the vintage the chemical reaction begins, but don’t stop, keep squeezing the bottle for a few more seconds.

What happened?
Vinegar (acetic acid) reacts with sodium bicarbonate and neutralizes it. In the reaction Carbon Dioxide (CO2) is formed and produces the bubbly and effervescent effect.
Food coloring gives color to your lava and the dishwasher detergent helps the effect to last longer.

Et voila!
Enjoy!