2 How do chemists measure?

One of the first units in the chemistry curriculum is about measurement. Students need to understand the metric system and how to work in metric units. This lesson is designed to help students understand the relative size of the metric prefixes, why it is critical to convert in the metric system, and how the metric system relates to their lives.

Learning outcomes

• Students will know the metric prefixes they will encounter in chemistry class and in their daily life.
• Students will understand how nanotechnology is being used in everyday applications.
• Students will be more aware of the chemistry they encounter each day.
• Students may develop an interest in a area of science they knew little about.
• Students create an advertisement for the use of nanoparticles in their daily life.

Teacher planning

Time required

2.5 class periods (85 minutes each)

Materials needed

• Metric system PowerPoint presentation
• Computer and projector for presenting PowerPoint, video, and/or other computer-generated projects
• Student handouts:
  • Gold nanoparticles lab sheet (Adapted from “Color My Nanoworld,” Journal of Chemical Education. Vol. 81 No. 4, April 2004.) Note: Lab sheet includes teacher notes.
  • Gold nanoparticles lab rubric
  • My nanoparticle: Student ad project
• Student computers with internet access for research on the student ad project

Lab materials

Amounts will vary with class size.

• gloves
• goggles
• HAuCl₄
• distilled water
• Na₃C₆H₅O₇
• 50 ml Erlenmeyer flasks
• burners
• vials
• graduated cylinders
• laser pointer

Pre-activities

• Introduce the students to the metric system, nanoparticles, and dimensional analysis. You may use or modify the metric system PowerPoint presentation under “materials needed” above. Students should have some idea of the relative size of the metric prefixes.
• Ensure that all students are familiar with proper safety procedures and have signed safety contracts on file in the classroom.
• Prior to class, prepare the solutions needed for the gold nanoparticles lab activity. See teacher lab notes below for instructions to prepare enough solutions for eight lab groups with four students per group.

Activities

Day one

1. Hand out the gold nanoparticles lab sheet and have students follow the directions to make gold nanoparticles. This may be one of the first lab experiences of the year, so it is necessary to remind students of the need to follow all safety procedures. They must wear gloves and goggles for this lab. They will learn how to find and use the proper pieces of lab equipment. Ensure that students are using the 25 ml graduated cylinders and that they are reading the tool from the bottom of the meniscus and at eye level.
2. During the lab, students should notice the color change that occurs as the nanoparticles form. This is due to a change in the oxidation state of the Au. Have students put their solutions in labeled vials and store them in a cool dark place to be used later in the year during the unit on light. They can be used in a spectrophotometer to show the wavelength of light that is absorbed by the purple colored particles. They may be used again during the conductivity lab to demonstrate that the nanoparticles are ions and that their solution will conduct electricity.
3. Have students complete the lab questions prior to the next class.
4. About 15 minutes prior to the end of class, introduce the nanoparticle ad activity by distributing the sheet “My Nanoparticle: Student Ad Project.” Ask students to read through the assignment, visit the web site referenced and come to class the next day with ideas for their project. Students may work with a partner or individually.

Day two

1. When students arrive to class the next day, give them 15 minutes with their group or partner to decide on their topic and write a one-paragraph explanation of why they chose that particular application.
2. Have students use computers to gather data about their application and they will begin to create their ads. Students may find useful information on the Project on Emerging Nanotechnologies website. The ads are limited in size and time as outlined on the student project sheet.
3. Have students complete their projects at home over the next few days and present their ads during class on a specified day.

Teacher lab notes

These notes are also on the nanoparticles lab handout.

1. Prepare the solutions according the following directions. The amounts given will prepare enough solution for eight lab groups. Increase or decrease the amounts to suit your needs.
   • Prepare 160 ml of 1.0 mM HAuCl₄ solution by dissolving 0.063 g of HAuCl₄ in 160 ml of distilled water. Equally distribute this solution into 8 vials that are large enough to hold 20 ml of solution. This solution is unstable and keeps only a few days, so make it fresh for the lab.
   • Prepare 25 ml of 38.8 mM Na₃C₆H₅O₇ solution by dissolving 0.25 g of Na₃C₆H₅O₇ in 25 ml of distilled water.
2. The nanoparticles can be stored and used during the unit on light to show that the red solutions absorbs green light with a wavelength of 520 nm.
3. The nanoparticles can also be used to show the difference in behaviors for an ionic and a molecular compound. Follow this procedure:
   • Prepare a 1 M solution of NaCl by dissolving 0.5 g of NaCl in 10 ml of distilled water.
   • Prepare a 1 M solution of sugar by dissolving 2g of sugar in 10 ml of distilled water.
   • Have students measure 3 ml of their nanoparticles and place it in a small vial. Label this vial as NaCl (ionic compound).
   • Have students measure 3 ml of the nanoparticles and place them in another vial. Label this vial as sugar (molecular compound).
   • Add 5 - 10 drops of the NaCl solution one drop at a time to the vial marked as NaCl. Record any color changes observed.
   • Add 5 - 10 drops of the sugar solution one drop at a time to the vial marked sugar. Record any color changes observed.
4. The ionic NaCl solution should cause the gold nanoparticles to aggregate and the solution will change from red to blue. The sugar solution should not show a color change because there are no ions available to aggregate the charged gold nanoparticles.

Assessment

• Students will write a short summary of what happened during the gold nanoparticles lab, focusing on the observations made during the lab. In addition, they will answer the questions at the end of the lab.
• The gold nanoparticles lab rubric is included as an attachment if you choose to implement a simple lab report format. The rubric, which also appears below under “Rubrics,” includes a summary of the method as well as observations and possible errors.
• The nanopoarticle ad project will be assessed using the rubric included on the “My nanoparticle: Student ad project” sheet. This rubric also appears under “Rubrics” below.

Modifications

The gold nanoparticles lab could be expanded to so that different groups of students work with differing concentrations of the sodium citrate solution. The sodium citrate binds to the gold nanoparticle surface and affects the size of the nanoparticle. This in turn affects the color of the final solution.

Alternative assessments

Rather than writing a written summary of the lab observations, lab groups could orally share their observations with the class.

Critical vocabulary

• Metric system
• Nanotechnology
• Nanoparticles
• Beaker
• Graduated cylinder
• Glass vial

• Next: What element would you be?

National Standards

In addition to meeting objectives of the North Carolina Standard Course of Study, this lesson plan addresses the following national standards.

National Science Content Standard A

• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry

National Science Content Standard G

• Science as a human endeavor
• Nature of scientific knowledge
• Historical perspectives

• Next: What element would you be?
• Previous: Author's overview

Learn more

• Exploring the nanoworld This site from the University of Wisconsin's Materials Research Science and Engineering Center offers easily digestible information about nanotechnology, including videos, lesson plans, and helpful explanations of the nanoscale.
• SmallTalk podcasts: Nanotechnology This podcast series from the Exploratorium features conversations about nanotechnology with leading scientists, thinkers, artists, writers, and visionaries, as well as quirky nanoscience stories in the news.
• Project on Emerging Nanotechnologies Offers an easily browsed list of nanotechnology-based consumer products.

Related topics

• Search LEARN NC for more resources on chemistry, hands-on, labs, measurement, metric system, nanotechnology, and science.