Acid Base Model Lab

Screen Shot from Second Day Analysis

Introduction

Methods

In class today, our teacher constructed a chemical gun for us. The gun used 2 ml of 1 M HCl with 8 ml of tap water to produce a 10 ml solution with a pH of 2.76. We measured the ph using a Vernier pH probe, CBL2 and a graphing calculator. 

These materials were placed inside a plastic test tube. The water solution was covered with vegetable oil, which floated on top of the water because it was less dense. The oil also did not react with either the acid or the baking soda that was placed on top of it.

During the next step, our teacher placed 6 grams of baking soda on top of the oil layer so that the baking soda would not react with the acid.

Finally, a rubber stopper was placed inside the test tube. My teacher then shook the test tube vigorously and I could hear and see that a gas was being produced. When my teacher released his finger over the top of the rubber stopper, it flew away.

Another student videoed the rubber stopper flying through the air so that we could measure the speed of the rubber stopper using frame by fame video analysis with Tracker Pro. 

In order to analyse the video, we had to first change the file extension so that tracker would open the video. Then, we opened the video and placed a ruler inside of it. We could tell that the video was distorted by changes in perspective, which made the video difficult to accurately measure.

Nevertheless, we then proceeded to add a point mass and we marked three frames of movement of the rubber stopper.

Data

	Start	End
pH of  water solution	2.76	6.4

Chemical Reaction

Na (CO3)2 + HCl -> NaCl + H2O + CO2

Conclusions

In this lab, we observed an acid base reaction that changed an acidic solution into a less acidic solution by releasing hydrogen gas. We know this happened because the pH changed from 2.76 to 6.7, which is a change on the order of 10,000 free hydrogens (H+) (for every hydroxide (OH-)) were released from the solution. This also proves that we formed water.

We also know we formed a gas, which we think is CO2 because we saw the bubbles and the pressure caused the rubber stopper to fly through the room.

We know we formed salt because we boiled a sample of water from the heterogenous mixture that resulted from the experiment. When the liquid was removed, the beaker was covered with salt crystals.

The carbon dioxide gas expanded quickly and built pressure inside the test tube, which is why the rubber stopper flew away. Eventually, the forces holding the stopper in place were less than the forces of the gas wanted to expand as more and more gas compressed the existing gas.

This labs shows that a chemical equation can be used to produce mechanical forces as a result of the properties of gas. We also illustrated that differences in density and solubility can be used to prevent chemical reactions. This is like a cell membrane blocking the free movement of materials inside our outside of a cell.

We also noticed that there was extra baking soda on the bottom of the test tube. We realized that the acid must have been the limited reagent because we ran out of it first, which allowed for left over baking soda.