1. Steps 1 and 2 will dissolve many of the components of the tablet, including the calcium, but will leave some insoluble residue. Filtering this residue out will remove part of the unwanted part of the tablet. It's part of the process of getting the calcium separate from the rest of the tablet. You rinse the flask and paper to make sure you got all the calcium. Notice the rinse is using the same acid that was used to dissolve the tablet. The flask you're rinsing is the one you dissolved the tablet in, not the one that the filtrate goes into.
2. No, you just want to know the mass and appearance of this part of the tablet for completeness. There's nothing interesting there.
3. You add the acid in specific amounts so you can calculate exactly how many moles of acid were used, I think. This will allow you to determine how many moles of CaSO4 are produced, which tells you how much calcium there is.
4. Again, the rinse is to make sure you don't lose any material. In this case you're trying to avoid losing any precipitate.
5. Correct.
6. The reaction looks right at first glance. The water that complexes with the product is not part of the chemical reaction but comes from the solution. So, you produce a little water chemically, but the CaSO4 product afterwards complexes with any water around, and most of that won't be the water produced in the reaction.
7. I don't see anything.
8. Don't know.
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