My first instinct is to test water solubility. At least some of those chemicals are water soluble. I don't know if any are insoluble. Wikipedia has this information. For example,
http://en.wikipedia.org/wiki/Sodium_carbonate
shows that Na2CO3 has a water solubility of 30 g/100 mL. Sucrose, which we all know is very soluble in water, has a solubility of 212 g/100 mL, which means that Na2CO3 should be much harder to dissolve in water than table sugar.
NaCl has a water solubility of 36 g/100 mL, but this is at a slightly higher temperature (25 deg. C). This is also better than that of Na2CO3, though these solubilities should be checked at the same temperature using the CRC Handbook or something similar.
Now, let's look at calcium sulfate. According to the Wiki, it's water solubility at 20 deg. C is 0.24 g/ 100 mL. Thus we can differentiate it from the others based on solubility.
Now you have two tools; inspection and solubility tests. Find the water solubility at room temperature for each of these substances and make sure the units match and the temperatures are the same.
Simplicity is key at first. You can try chemical tests for further info, but start with simplicity.