What percent (by mass) of granulated sugar is fructose, and what percent of it is sucrose?

Background:
We are doing a colligative properties lab in my class where we are to add 20 grams, 40 grams, 60 grams, and 80 grams of sugar to 100 grams of water, and use the change in the water's boiling point to find the molecular weight of sugar.

I thought that granulated sugar was simply a homogeneous compound containing sucrose, whose dissacharide molecular structure contained a fructose molecule bonded to a glucose molecule, but my teacher told me that granulated sugar is in fact a mixture containing fructose and sucrose molecules held together by intermolecular forces. Which is it, and how should I tackle this issue in my lab writeup?

I'm at a loss. I thought, and think, the same as you and from what I can read on the web that is still true. Also I read that solutions of sugar could sit for years without the glycosidic bond being broken. Nothing was mentioned about temperature; it could be that boiling the solution in the lab accelerates the hydrolysis but even if that were true you would have a mixture, in my opinion, of sucrose, glucose, and fructose. What to do? I don't know what to tell you. Sometimes I disagreed with my prof(s) but I did it very carefully.

To determine the percentage (by mass) of fructose and sucrose in granulated sugar, you can approach the problem in the following way:

1. Understand the composition of granulated sugar:
Granulated sugar is primarily made up of sucrose, which is a disaccharide consisting of one glucose molecule bonded to one fructose molecule. Sucrose is a homogeneous compound.

2. Distinction between granulated sugar and powdered sugar:
It's important to note that granulated sugar is different from powdered sugar. Powdered sugar is essentially granulated sugar that has been ground into a fine powder and often contains a small amount of cornstarch to prevent clumping.

3. Consider impurities in granulated sugar:
While sucrose is the main component of granulated sugar, there might be impurities present in the form of other sugars such as fructose, glucose, or maltose. These impurities can vary depending on the source of the sugar and the processing method.

4. Laboratory approach and limitations:
In your colligative properties lab, you can use the change in the water's boiling point to find the molecular weight of sugar. However, this method does not directly distinguish between fructose and sucrose.

5. Additional experiments for determining fructose and sucrose composition:
To specifically determine the percentage (by mass) of fructose and sucrose in granulated sugar, you would need additional experimental techniques such as chromatography, mass spectrometry, or enzymatic methods. These techniques can help identify and quantify individual sugars present in the sample.

6. Addressing the issue in your lab writeup:
In your lab writeup, you can acknowledge that while granulated sugar is primarily composed of sucrose, it may contain other sugars as impurities. Mention the limitations of your experimental approach and acknowledge that determining the exact composition of sugars in granulated sugar requires further analysis beyond the scope of the current experiment.