what happen to white sugar when continuous heat is applied?

Question

please help... co'z its my assignment for tommorow!!!

Answer 1

It caramelises - it starts to break down into carbon and steam, and turns brown. Eventually it would turn black.

Answer 2

The following experiment will explain the results :
ADVANCE PREPARATION
Gather the materials.
TIPS
• Have the students work in groups of two or three.
• Teachers should closely supervise students when an open flame is being used.
MATERIALS
• 250 ml beaker or medium size jar
• stirring rod or spoon
• metal spoon or jar lid (disposable)
• bunsen burner or alcohol lamp
• tongs
• measuring spoon
• water
• sugar

PROCEDURE
Part I:
1. Measure about one tablespoon of sugar and add it to the 250 ml beaker. Add about 150 ml of water to the beaker.
2. Weigh the beaker and the sugar water mixture before stirring the mixture. Record the weight.
3. Now stir the mixture until the sugar is completely dissolved. Weigh the full beaker again and record the weight.
Part II:
1. Now measure another tablespoon of sugar and place it in the metal spoon or jar lid.
2. Weigh the spoon (lid) and the sugar together and record the weight.
3. Use the tongs to hold the spoon or lid containing the sugar over the open flame of the bunsen burner or alcohol lamp. Be sure you are wearing safety goggles for this part of the activity. Heat the sugar until vapors start to rise and the white crystals turn to a crusty brown substance.
4. After a portion of the sugar has turned brown then remove the spoon or lid from the heat and allow to cool. Weigh the container and the sugar again and compare the weight of the container and sugar after heating to the container and the sugar before heating.
5. The sugar will be baked onto the metal so discard the metal after it cools.

6. Dispose of liquid with water in sink; collect solid in waste container.
SUGGESTED FOLLOW-UP
Part I:
1. How did the weight of the container and sugar compare before heating to after heat-ing? If there was a difference between the weights what do you think happened to the “missing" material? If there was no change, how could this be when the sugar disappeared?
The weight of the container and solution before dissolving the sugar and after dissolving the sugar should be the same. The sugar simply went into solution when the crystals were broken apart by the water. Therefore nothing was lost to or gained from the outside environment.
2. Where did the sugar go when it was dissolved?
The sugar went into solution. The molecules of water surrounded each molecule of sugar after the crystal structure of the visible sugar grain was broken up.
3. When the sugar dissolved was this a physical change or chemical reaction? Explain.
The dissolution of sugar into water is a physical change. This is only a change of state, no chemical bonds are being broken or formed. The sugar can be separated from the water by a physical change - evaporation, boiling, etc.
Part II:
1. How did the weight of the container and sugar compare before heating to after heat-ing? If there was a difference between the weights what do you think happened to the “missing” material? If there was no change, how could this be when the sugar disappeared?
The sugar and the container should have weighed more before the heating. The difference in weight is due to the loss of water from the chemical decomposition of the sugar.
2. Was the change in the sugar chemical or physical? What is your evidence?

The change seen is a chemical reaction. The evidence that points to this fact is the change in the sugar’s color from white to brown, and the production of a gas that can be seen rising from the sugar. Both of these are signs of a chemical reaction.

3. What substances do you think were produced from the heating of the sugar?
The products from this decomposition are water and carbon.