My PBL Project

Introduction

In this project I will be observing the effects of saturated sodium carbonate solution on a dilute solution of hydrochloric acid and universal indicator. If done correctly, colors will develop as the sodium carbonate sinks to the bottom and carbon ions spread upwards and neutralize the acid.

Driving Question

How does saturated sodium carbonate solution affect a dilute solution of hydrochloric acid and universal indicator?

Materials

  • Test tube, Large, 20X150 mm

  • Test tube rack

  • Beral-type pipet, 2

  • Hydrochloric acid solution, 0.1 M, 20 mL

  • Sodium carbonate solution, saturated, 6 mL

  • Universal indicator, 3 mL

Procedure

  1. Add about 3 mL of universal indicator solution and 20 mL of hydrochloric acid solution to a large test tube. Swirl the test tube to mix. This should produce a bright red color.

  2. Fill a Beral-type pipet with sodium carbonate solution. (This is approximately 3 mL)

  3. Tilt the test tube slightly and slowly squeeze the sodium carbonate solution down the side of the test tube to the bottom. The sodium carbonate solution will sink to the bottom of the test tube. Refill the pipet with more sodium carbonate and add to the test tube in the same way. (Total amount of sodium carbonate added is 6 mL)

  4. Place the test tube on the test tube rack and observe the changes.

  5. Colored layers form gradually resulting in a rainbow spectrum of colored layers in the tube that will remain for several days if left undisturbed.

Observations and Data

In the first trial, I didn't tilt the tube which led to the chemicals mixing correctly and making a dark green liquid which I had to pour down the sink. But in the second trial, I tilted the test tube like I was suppose to and added the sodium carbonate solution which made the dark green color again, but after a few minutes you could see the layer of colors start to form, which was actually pretty cool.

Calculations

Universal Indicator Solution - 3mL

Hydrochloric Acid Solution - 20mL

Sodium Carbonate Solution - 6mL total

Analysis and Conclusion

When you tilt the test tube, it allows the sodium carbonate solution to slowly sink down to the bottom of the hydrochloric acid solution-universal indicator solution mixture and after a few minutes it creates a rainbow spectrum of colored layers. But if the test tube isn't tilted, the mixture just creates a dark green color when the sodium carbonate solution is added, but unlike the trial where the test tube is tilted, it doesn't eventually turn into colored layers.

Scientific Principle

To create the colored layers, a universal indicator is added to the mixture of hydrochloric acid and sodium carbonate. The universal indicator is an acid-base indicator which is a weak base or acid. It indicates the concentration of H+ ions in a solution through color change. This color change is caused by the separation of the H+ ion from the indicator itself. The separation of a weak acid indicator led to the solution's change in color.

Safety Regulations

Dilute hydrochloric acid and saturated sodium carbonate solutions are skin and eye irritants. Avoid contact of all chemicals with eyes and skin. Universal indicator solution is alcohol-based and is therefore inflammable. Keep away from flames and other ignition sources. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Review current Material Safety Data Sheets for additional safety, handling, and disposal information.