Why would the same amount of gas be produced even if we increase the amount of baking soda?

Explanation:

If you are not increasing the amount of vinegar, the adding more baking soda has nothing to react with. The limiting reagent is vinegar (or some other acid).

The usual reaction is

HC2H3O2 + NaHCO3 ===>  NaC2H3O2 + HOH + CO2 which is the gas being expelled.

If you increase the NaHCO3 nothing more will happen until you increase the vinegar.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"