Experimental Procedure PART E: Interpreting conductivity changes during a chemic

Question

Experimental Procedure PART E: Interpreting conductivity changes during a chemical reaction. As you make your observations, write a few sentences in the space directly after each experiment that clearly describe the results. Your discussion should address: the trends in the data and what causes the changes in the conductivity readings as you conduct the experiments Furthermore, discuss any of your predictions that were incorrect and why they were incorrect. Hint: Keep in mind that there are reactants, products, and leftover excess reactants. 1. Instructor Demo: Measure the conductivity 5 mL of 0.1 M sulfuric acid and 5 mLof saturated (approx. 0.1 M) barium hydroxide separately with the conductivity meter. Add a few drops of phenolphthalein to the barium hydroxide solution. Add the acid solution in several small portions with constant stirring (use a stir rod) and measure the conductivity in between each addition. The solution should lose its pink color, but if not, add more acid until the pink disappears, measure the conductivity, and add a few mL excess of acid and take one more measurement with the conductivity meter. Barium compounds should be disposed of into the waste container in the hood 2. Measure the conductivity of 5 mL volumes of 1.0 M acetic acid, 1.0 M formic acid, and 1.0 M aqueous ammonia in 10 mL graduated cylinders with the conductivity meter. Now add the volumes together, mix with a stirring rod, and measure the conductivity of the resulting solution. This solution can be disposed by pouring it down the drain. 3. Measure the conductivity of 5 mL of glacial acetic acid (concentrated; located by the sink Now, add 5 mL of water and measure the conductivity again. Now, add a small strip of magnesium ribbon, wait for the reaction to cease and take one last conductivity measurement.

Explanation / Answer

In (1), the balanced molecular reaction taking place is as follows:

H2SO4 + Ba(OH)2 ---> BaSO4(s) + 2H2O

The net ionic reaction is as follows:

Ba2+(aq) + SO42-(aq) ----> BaSO4 (s)

In (2), the following reactions take place:

NH3(aq) + CH3COOH ---> CH3COONH4

The ammonium acetate formed above exists as NH4+ and CH3COO- ions in solution.

NH3(aq) + HCOOH ---> HCOONH4

The ammonium formate formed above exists as NH4+ and HCOO- ions in solution.

So the overall equation is written as:

CH3COOH + HCOOH + 2NH3 ---> CH3COONH4 + HCOONH4

In (3), the balanced reaction taking place is:

Mg(s) + 2CH3COOH ---> Mg(CH3COO)2 + H2(g)

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