Rate of Reaction - removing silver tarnish

[MarioLuigi]

The experiment I'm conducting measures the rate of reaction for varying baking soda (sodium bicarbonate) concentrations. I will be putting tarnished silverware into a bath of water and soda within a beaker that is lined with aluminum foil. I conducted this experiment, and my trials suggest an exponential trend. Now when calculating the rate of reaction, I need the equation in order to find the rate order equation. Using prior research, I can determined the equation to be 3 Ag2S(s) + 2 Al(s) + 3 H2O (l) –––> 6 Ag(s) + 3 H2S (aq) + Al2O3(s). I don't see the baking soda coming into play in this equation, despite being the changing variable (as in factor affecting the rate of reaction). Is this equation being used incorrect, or is there a reason towards why baking soda isn't being incorperated. I assumed I cannot continue to find the rate of reaction without the equation with the changing concentration (being the baking soda). Thank you for your time, please help I'm struggling IA due soon 

[kw0573]

You should understand the reaction with solid aluminum is a redox reaction. That is not the only possible reaction. You should write the one instead involving baking soda instead of aluminum. If you have not yet learned about redox reactions, you should probably choose a different experiment for the IA. Wish you all the best!