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Name: Andrew P.
Status: student
Age: 14
Location: N/A
Country: N/A
Date: 10/16/2004


Question:
In my earth science class we were told to grow sugar crystals in two weeks with no knowledge of the process. He recommended that if we were not successful in growing sugar crystals to try using alum instead of sugar. I have found many different suggestions on how to make them with alum but they all supposedly will take about two weeks to make and I have one week left to grow them. What I need to know if there is a possible way to make alum crystals within one week of adequate size (around 3 to 4 inches). If there is a way to do this I would appreciate it. If not I would be helpful if you could tell me a sure way to make good sugar crystals within this time. If possible tell me why I cannot make sugar crystals in my home. I followed the correct procedures that I was told. I add 200 grams of sugar to 26oz. of water and boiled until it was gone. I put it in a jar and covered the container and it has been a week and I have not gotten any crystals.


Replies:
Andrew,

Do not give up. The experiment can still be done in the time you have. Before I give you the information however, I want you to understand some of the principles of crystal growth.

1) Crystals form when the normally solid substance come out of solution. This means that the solution has to be concentrated or contain as much of the solid substance as it can possibly hold. The more solid is in the solution, the more crystallization can happen.

2) Hot solutions can dissolve more solid than cold ones. This means that if you start of with a hot solution, when it cools, the solution will not be able to hold on to the solids and the solids will crystallize out (assuming that #1 above is true).

3) Big crystals have to be grown slowly. You can certainly grow crystals from extremely hot solutions and extremely concentrated solutions, but the crystals will come out of solution very fast that the crystals will tend to come out everywhere in the solution. If you want to have big crystals, they will have to grow slowly and only from certain spots.

4) Crystals have to grow on something - either other crystals or on some rough surface.

5) Evaporation helps to concentrate a solution.

Keep the ideas in mind.

Next, you have to make sure that you are doing this experiment in as safe an environment as possible. This means that you do not do this experiment by yourself (some adult you trust should be watching), and you have to remember that you will be working with hot - and sticky - solutions. If they get on your skin, not only will it burn, but it will be hard to remove. So please make sure that you have protective clothing, protective eyewear, and good equipment.

Now to the growing of crystals -

You will need a mason jar or some thick, heat resistant glass container. Check it for cracks, if it has any, get rid of it, find another container. Clean it well. You need a bamboo skewer (the ones used to make kebabs). You also need some paper to cover the jar (do not use the lid that came with the jar) just to keep off dust. You will also need a pan of water to place under the jar to keep ants away.

Bring about a cup or so (depending on the size of your jar) of water to a boil (remember #2 above), add sugar until no more will dissolve (remember #1 above). Allow the solution to cool slightly and then pour it into the mason jar. Place a pan of hot tap water on some sunny spot of the house, and then place the mason jar on top of the pan of water. Stick the bamboo skewer into the solution (think #4). Cover the jar with paper - not tightly - you want the water in the jar to evaporate slowly (think #5).

The only thing to do is to replace the water in the pan (not the jar) to continue to keep ants away - in about 2-3 weeks there should be plenty of crystals on your stick.

Now, think of what is different with this procedure and what you tried to do before.

Finally, if you really need to get the crystals made sooner than 2-3 weeks, think of #1 and #3. If you make your solution really concentrated, crystals will come out faster, but it will also mean that they will tend to be smaller.

The way to make the solution really concentrated is to boil as much water out of your solution (until the liquid is more syrup-like than water-like) - but this is VERY DANGEROUS, splattering of very hot droplets will certainly occur, and the surface of your stove can get messy (clean up right afterwards). Be sure to check with a responsible adult first, and make sure they are there watching you do the experiment if you want to try making more concentrated sugar solutions.

Greg (Roberto Gregorius)


Hi Andrew!

to grow crystals is called an art so it is better having no hurry, but since you have a class appointment let us help you with your sugar crystals. I hope you still have time to do it.

Try this recipe:

Boil about 250 ml (a cup) of distilled water. Let it stand a few minutes and than pour it into a glass recipient that can stand the temperature. Very slowly stir in the hot water about 3 cups of refined sugar; adding a teaspoon each time and stirring continuously.

Do that until the sugar stops dissolving. You can see then some of it begins to collect at the bottom. That means you made a saturated solution (depending on circumstances, even a super-saturated one).

Now tie the extremity of some string around the middle of a pencil, and at the other extremity of the string tie a nail or a clip.

Place the pencil horizontally over the recipient leaving the string down to the middle of the liquid volume, not touching the bottom.

Cover lightly the recipient opening to keep out dust and let it stand in a quite place undisturbed. Hopefully within 24 hours you will see some crystals beginning to grow over the nail.

If you would like prettier crystals you can add at the water some drops of food coloring stuff.

You can try different temperatures to begin with and also different sugar quantities.

Good luck!

Thanks for asking NEWTON!

Mabel
(Dr. Mabel Rodrigues)


You are probably a victim of a supersaturated solution of sugar. You need a seed crystal to ensure that a crystal will start to grow when you cool the solution to the solubility point. You did not mention that you had seeded your solution. If not, that will cause a problem. Whether you can beat the time line I am not sure because growing good crystals is an art -- very little science, and a lot of good luck. The web site below (despite its smart aleck tone) has a lot of good suggestions for growing crystals.

http://www.crystalgrowing.com/recipes/sugar/sugar.htm

Good Luck

Vince Calder


Ah, yes. Andrew, I had this same difficulty last year with my daughter's science project. Sugar crystals can be stubbornly difficult to start. We were not covered in 3" crystals at the end, either.

Big tip: your recipe has far too much water or too little sugar.

First thing you need to ask yourself is, how much sugar can dissolve in water at room temperature?

By heating the water, you force it to dissolve _more_ than that percentage. Because, of course, the hotter the water is, the more sugar can dissolve in it. Then, when the solution cools down it is "super-saturated" and it is ready to start growing solid sugar instead of dissolving it.

The procedure you have gotten is, unfortunately, wrong. The amount of sugar is much too small. 200 grams of sugar will soon dissolve in 26 oz. of water, without even heating it, and then it will keep on waiting for more sugar to gobble up. If you dangle in the solution a string with seed crystals on it, this "sub-saturated" solution will merely lick the string clean.

You need to find the true solubility limit, yourself. You could waste far more than a week doing it by trial-and-waiting experiments, or you can web-surf. Some answers are hard to get there, but his one's everywhere.

Go to , type in the box the words "solubility sugar" without the quotes.

It gives you a list of web-sites to try.

At the very top of the list is this free sugar-calculating service:

.

This web-page has boxes where you enter the temperature of the water (for you, either 25C or 100C), the amount of sugar and water and sugar to be mixed (prepare to convert your oz. of water to grams of water), And when you hit the "evaluate" buttons it tells you the density of the solution, the concentration in other units, the maximum solubility at your temperature, and even the viscosity of the liquid.

I think you will find that you need many times more sugar for that amount of water. I think somebody dropped a zero from 2000grams, and that is how your erroneous recipe was launched into an unsuspecting world. (Do not use that number, it might be wrong too.) Anyway, we mixed about 5 cups sugar and 1 cup water. Really! When it is cold, you wonder if there is enough water to even wet all that sugar. After a little slow boiling and stirring, it is rather thick but it is actually clear. It is also 30-40% heavier than plain water. When it cools down it is really thick, and still clear, and probably still not growing crystals. (By the way, Honey is a sugar solution temporarily not growing crystals.)

Viscous solutions of many kinds often refuse to start crystals spontaneously, even when they are supersaturated. The solution wants to get rid of some sugar, but it does no't quite know how to. This is when you need to provide "nucleation points" by inserting "seed crystals" into the cool solution.

Get at least 6 feet of string. Cut it into 8-12 inch lengths. Tie a simple knot in each end if you do not want it to unravel. Wet them well, then pad them off with paper towels, then dip them in your thick sugar solution. Take them out and lay them out straight on wax paper, side-by-side. Put the wax paper on a metal tray and dry it in your oven at very low heat, perhaps 200F. This forces the water to evaporate and crystallizes the sugar in the string. Now you have a bunch of "crystal-starters", each good for one try. Tie one end around a pencil or popsicle stick, or through a hole in a cardboard square. This can bridge over the top of a plastic cup, allowing the string to dangle into the solution. Only use 1 string in each container of solution, so you always have more for another try if this one does not work.

If it is going to work, the string will have visibly larger crystals by next morning. And maybe the water-surface will be growing a crust, too. If it does not work, the string will be missing the tiny crystals it had.

This still did not work for us, so we had to put the plastic cups on cardboard on a warming-plate, and wait a couple of days. Suddenly we got many crystals, but not huge.

After our fiasco I got alum at the drugstore. Simple chemicals are no longer widely used as remedies; they had to special-order it for me. This might take time you do not have, so call them to ask. Alum does have the advantage of a more reasonable solubility limit (only about 15% at room temperature, much more when hot), and lower viscosity, and easier nucleation.

Plenty of web sites on alum crystals too, one at:

.

I keep wishing it was feasible to assemble a crude machine: applying about 10 Watts of heat to a pile of solute at one end of a solution bottle, and growing crystals at the cooler other end. That might quietly grow great crystals. Part of the problem is that there must be some slow stirring. You would think that hotter solution rises, creating convection-stirring, but in crystal-growing the flow often stalls instead. Problem is, hotter solutions dissolve more solute, making them heavier. If that made backwards convection, fine, but I am not sure it does that either.

That would require applying heat and sugar at the top, and letting crystals grow at the bottom.

I cannot think of how to build it, that way. Maybe you could. With heat and powder at the bottom of a jug, you need a gentle mechanical stirring device in the middle. "Uncle Al" seems to be more optimistic than I am:

.

He has a pot with alum and heat at the bottom, and no stirring.

Please look at

.

He has simple solubility charts on sugar&water. And pictures of big sugar crystals. He seems to hint that my problem was I did not cool down very slowly, over several hours. You might have ways to make this happen. Even if you are merely turning down an electric warmer in sudden 20-degree-F steps, that helps.

With these understandings, you will have to just "wing it" and try about 3 things fast and easy. That would be the best way to get something done here. Cautious handling of boiling solution is the only thing to be careful about.

Simple but good directions at

.

If anybody in your class brings in 3" crystals in only 2 weeks, write me so I can eat a hat.

Jim Swenson



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