Need help with an experiment question

Hi! There was some homework questions related to an experiment that I had some trouble with, I also wanted to see if I'm correct with some of them.
So the purpose of this experiment is to determine the actual mass of sodium hydrogen carbonate in an alka-seltzer tablet and compare it with the mass given on the product label. (the following mass data from the experiment is below)
Objects used:
-Seven 250 ml Erlenmeyer Flasks
-50 ml graduated cylinder
-Dropper
-Vinegar (is dilute ethanoic acid, HC2H3O2(aq))
-7 Alka-Seltzer tablets
Here are the questions
1. Identify the dependent variable in this experiment.
2.Identify the independent variable in this experiment. 
3.Identify 2 controlled variables in this experiment. 
4. determine the mass of the sodium hydrogen carbonate that reacted in each of the 7 trials of the investigation.  In the data, you can easily determine the mass of carbon dioxide released because it is the cause of the difference in mass between the beginning of the reaction and the end.  In order to determine the mass of the sodium hydrogen carbonate that reacted, you have to use stoichiometry to compare the CO2 product to the NaHCO3 reactant. The chemical equation for the reaction of vinegar (HC2H5O(aq)  with sodium hydrogen carbonate is:                                                          NaHCO3(aq) + HC2H5O(aq) NaC2H5O(aq) + H2O(l) + CO2(g)