Aug 27th, 2013 — Chemistry

Introduction to Chemistry - Antacid and Vinegar

Introduce your students to core chemistry concepts as well as data collection and analysis with a quick demonstration using common household chemicals. This classic demonstration of a chemical reaction is quantified and enhanced with pH, temperature and conductivity measurements using the Advanced Chemistry Sensor. This quick demonstration will help the students think about some of the concepts that they will see throughout the year and the types of measurements that they can make to explore those concepts.

Demonstration

  • Add ~60mL of water and ~60 mL of household vinegar to a 150mL beaker.
  • Ask the students what the pH should be. Most will assume low since it is an acid.
  • Put the pH, Temperature and Conductivity Probes in the beaker and create a graph of pH vs. Time and a digits display of pH.
  • Ask the students to predict what will happen to the pH once the antacid tablet is added.

pH vs. Time

pH v time
Overall, the pH increases as the reaction occurs. After the first tablet was added the pH increased, then leveled off. At around 100s, another tablet was also added causing the pH to increase again. Gas formation is also noticeable in the beaker.

Since the Temperature and Conductivity Probes were also in the solution, there are more opportunities for measurement-based explorations of the system.

  • Ask the students to predict the temperature change as the reaction proceeds.
  • Ask the students to predict the conductivity change as the reaction proceeds.

pH and Temperature vs. Time

Temp v Time
>Most students will be surprised to find the temperature decreases during this endothermic reaction. As each tablet is added, the temperature decreases while the pH increases.

pH, temperature and conductivity vs. Time

pH, Temp and Conductivity vs. time
The conductivity relationship is more complicated because it will be affected by the weakness of the acid, the formation of ions in the reaction and the formation of a gas.

The reaction of antacid and vinegar provides a nice visual indication that a chemical change is talking place. By monitoring the reaction with probeware, core chemistry concepts (acids and bases, electrolytes, and thermochemistry) can be also introduced.

Student Extension

Time permitting, have the students perform other experiments with beakers of “unknowns” to see of visual observations match probeware data.

  • The students can mix one “unknown” beaker containing 100 mL of water with blue food coloring and another beaker with 100 mL of yellow food coloring.

There will be a color change to green, but the measurement data will not indicate a chemical change

  • The students can mix one “unknown” beaker of 100 mL 0.1 M HCl and another beaker of 100 mL 0.1 M NaOH

There will be no obvious visual indication of a chemical reaction, but the measurements will indicate that a change has taken place.

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