My PBL Project

Driving question: How does tonic water glow?

Materials:

Visible light Source

UV light source

Beaker-600 ml

Tonic Water, 500 ml

Procedure:

1. Place 500 ml of tonic Water in a 600 ml-beaker. Note the appearance of the tonic water.

2. Turn off all the lights and completely darken the room. Place a white paper/ white background behind the beaker to increase visibility of a color change. Turn on the UV light and shine it on the tonic water. Observe that the tonic water appears fluorescent blue in color.

3. Discuss your observations, inferences, explanations and extensions.

Scientific Principle/Essential Understanding:

This will show how light interacts with matter. Also the way electrons behave under UV light.

Safety Regulations:

This activity doesn't really use harmful chemicals. Tonic water isn't really harmful. However, just to be safe, always wear chemical splash goggles and apron.

Scientific Principle/Understanding:

The Tonic water glows blue under UV light because the UV light makes the electrons glow. That's why it appears fluorescent blue. The water is florescent because of the quinine that is present in the solution.

Post Investigation; Task 6:

I chose to do a second driving question.

The sun also emits UV Radiation, so would tonic water also glow under the sun?

Here is the tonic water with a white background

Here is the tonic water with a black background

The answer to the second driving question is not really. As you can see in the photo, the tonic water appears regular in color with both a black background and a white background. However, you can see that the water appears almost blue in color. That does not look like the UV light's illumination of the tonic water but rather the black background's way of interacting with light. Compare the black background photo with the photo of the tonic water glowing in the investigation of the first driving question. You can see that the colors don't match so therefore the answer is not really.

Further investigation of Task 6:

The sun's light that it emits is mostly visible light. It does emit UV light, but that's not the most abundant emission. Also, the earth has an ozone layer that is absorbing most the UV lights. The UV lights that are absorbed are mostly UVB and UVC rays. So most of the UV rays that reach the earth are UVA. Now, the difference in each type of UV ray is the wavelength.

UVA: 400nm-320nm

UVB: 320nm-290nm

UVC: 290nm-100nm

The kind of UV light that I used had a wavelength on 390nm, so it would be a UVA light. But then I asked "If the UV rays that reach the earth are mostly UVA rays the how come the sunlight couldn't cause the tonic water to glow?" I then realized that the difference between when the UV light was illuminating the tonic water solution and when the sunlight was illuminating the solution was the fact that visible light was not present. I showed the tonic water with a black background under the light to help increase the visibility of a color change if there was going to be one. I chose black because a white background was needed in the dark, so I concluded that a black background would also be needed in the dark.