# Summer SAVY Session 2, Day 4 – Common and Practical Chemistry (Pao)

Posted by on Thursday, June 22, 2023 in blog, SAVY.

Day 4: Today we learned about light waves and reviewed topics from earlier in the week. We began the day by doing a strawberry DNA extraction. In this extraction, students added a salt and detergent mixture to smashed strawberries. The detergent helped the strawberry cells lyse by damaging the cell membrane, releasing DNA from the nucleus of the cell. Because the salt neutralized the negative charges in the DNA backbone, the DNA strands did not repel each other but instead clumped together, allowing students to use a skewer to take out the DNA.  We also discussed how DNA can be used after it is extracted. Often, it is stained with ethidium bromide, which allows DNA to emit light so that it can be seen or easily for processes such as gel electrophoresis. This activity allowed us to review information about charges and move on to discussing light!

We talked about the basic components of waves (amplitude, wavelength, frequency, speed, peaks, and troughs) and learned how to calculate frequency, speed of light, and amplitude by using the equation c = λv, in which c is the speed of light, λ is the wavelength, and v is the frequency. While most students found it challenging at first to use algebra to isolate the variable of interest, they asked many questions and worked hard so that they could understand the calculations. Then, students completed a lab in which they tested the efficacy of different types of sunscreen. Students placed UV-sensitive beads into a few bags, and they covered the bags in different types of sunscreen. Then, they went outside and placed the bags in the sun to see if the beads would change color when exposed to UV light. Most students found that sunscreens with higher SPFs were more effective by noticing that the beads in bags with higher SPF sunscreens on them had smaller changes in color. However, not all students got the same data, so we had a great discussion on sources of error and how to improve the lab next time.

Some key takeaways from today include:

• The electromagnetic spectrum consists of different types of waves with various wavelengths and unique characteristics
• Waves are defined by properties such as speed, wavelength, frequency, and amplitude. Speed, frequency, and wavelength are related, as shown in this equation: c = λv
• UV light can lead to color changes in some materials, such as UV color-changing beads and t-shirts with particular dyes