The UDL will be provided by me and the app and code to download the software will also be given by me.
Please add the attached UDL file to chemlab. Then, after running the experiment, report your data via the submission form below.
Important note: The ammonium molybdate solution in the procedure is called color reagent in the list of chemical in chemlab.
Background:
Coca-cola contains acids including carbonic acid which is formed from the dissolution of the carbon dioxide in the water, and phosphoric acid, which is used to give it a little “kick” when you are drinking it. In previous experiments, we were able to find the amount of acid by titrating with a standardized base such as sodium hydroxide. In this case however, titration with sodium hydroxide will titrate both acids. Therefore, we need a method to distinguish one acid from another.
Titration of the acids.
The chemical reactions for the titrations of the acids are given below. I will let you balance the equations.
H2CO3(aq) + NaOH(aq) → Na2CO3(aq) + H2O(l)
H3PO4(aq) + NaOH(aq) → Na3PO4(aq) + H2O(l)
Since sodium hydroxide is a strong base, it will react with each proton on the acids. However, because sodium carbonate is a weak acid, we will need to find an appropriate indicator to use, one that will change in the desired region. We will talk more about this before the lab.
Determination of the phosphate.
Remember that in solution, the phosphoric acid solution exists as hydrogen ions and phosphates. If we can find determine the concentration of the phosphate, we can relate this to the concentration of the phosphoric acid. For example, let’s say we found a concentration (in molarity) of 0.002M PO43-.
We can see that the ratio of phosphoric acid to phosphate is 1:1 so that the molarities will be the same. Likewise, we will use 0.01 KH2PO4 as our standard, because we do not care about the potassium and the hydrogens, we only care about the disassociated phosphate, which will react with the ammonium molybdate.
In general, this is what occurs…
Standardized potassium dihydrogen phosphate is dissolved in solution. This dissociates to give us a known concentration of phosphate in solution. This dissociated concentration of phosphate reacts with the ammonium molybdate/ammonium metavanadate solution producing a characteristic color. The amount of color is dependent on the amount of complex produced by the reaction. Using a spectrophotometer, we can measure the absorption of light passing through this solution. As the amount of color increases, the amount of light that can pass through the solution is decreased. This is because light is being absorbed as it passes through the solution.
The spectrophotometer 20 is used to measure the amount of light that passes through a solution.
The procedure and activity sheet are attached.
What to submit
Your saved .lab file (model chem lab file)
Your completed SIM Phosphates in cola STUDENT worksheet showing answers and work. Work should include units and their proper cancellation
