What effect does Baking Soda and Citric Acid have on a soft drink?
Actually if we care just about the reaction between Baking Soda ($\ce{NaHCO3}$) and Citric Acid ($\ce{C6H8O7}$) the following reaction should ensure :  

$$\ce{3NaHCO3(aq) + C6H8O7(aq) -&gt; 3 H2O (l) + 3 CO2(g) + Na3C6H5O7(aq)}$$ 

So basically the reaction should produce water, carbon dioxide and trisodium citrate (as known as E331 : a food additive)