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Nov. 18, 2011

Investigating Solubility

by Girlstart

In this activity, kids become forensic scientists to investigate the solubility of various inks. Students observe if the ink of each marker separates into different colors when placed in water. The Girlstart girls used their knowledge of chromatography to solve an inky mystery. Using household items – various pens, markers and coffee filters – learning about chromatography is fun and easy!

Overview:
Students analyze how different types of ink react when absorbed by water. Students use chromatography to identify the source of a note written in black marker. Students identify substances that are soluble and insoluble in water.

Objectives:

(5.5A) Classify matter based on physical properties, including mass, magnetism, physical state (solid, liquid, and gas), relative density (sinking and floating), solubility in water, and the ability to conduct or insulate thermal energy or electric energy.
(5.2) Scientific investigation and reasoning. The student uses scientific methods during laboratory and outdoor investigations.
(4.5A) Measure, compare, and contrast physical properties of matter, including size, mass, volume, states (solid, liquid, and gas), temperature, magnetism, and the ability to sink or float.
(4.2) Scientific investigation and reasoning. The student uses scientific inquiry methods during laboratory and outdoor investigations.

Materials:

  • Engineer’s Journal
  • Cotton cloth cut into 2 in. x 2 in. squares – two per group
  • 5 different brands of black markers (Crayola, Sharpie, and a mix of permanent and water soluble) – for each group
  • 9 oz. clear, plastic cup of water – one per group
  • Water
  • Hand lenses or one digital microscope such as a Proscope – per group
  • Paper towels
  • Coffee filters – five per group
  • Copy paper
  • Forensic Scientist Poster

Vocabulary:

chromatography a method used to separate the components of a mixture; chroma means color, and graph means to write.
Dissolve when one material forms a solution with another material
physical properties the characteristics of a substance that can be observed or measured without changing the substance
pigment the chemicals that make up color
solubility a measure of how much of one substance will dissolve in another substance
solvent the substance that dissolves another substance; water is the solvent in a saltwater solution.
Solute the substance that is dissolved; salt is the solute in a salt water solution
solution a mixture with one substance spread out so evenly in another substance that you cannot tell the two substances apart
water-soluble can be dissolved in water

Preparation:

  • Gather and test markers prior to teaching the lesson.
  • Gather cotton cloth and cut into small squares (approx. 2 in. x 2 in.)
  • Make one set of the Is it Water-soluble? card match for each group. Cut out the cards and place in plastic bags.
  • Make a color copy of the Forensic Scientist poster
  • Make copies of Investigating Solubility Results page for each student.

Careers:
Forensic Scientists use scientific principles to analyze biological, chemical, or physical samples taken into evidence during a criminal investigation. These scientists perform lab work, keep detailed records, write reports, and explain and defend their findings in a courtroom. Forensic scientists use scientific knowledge to solve real-life problems.

Engage:

  1. Organize students into small groups. Give each group a paper towel to place on their desks.
  2. Give each group two small pieces of cotton cloth, a black, Sharpie marker, a black, Crayola marker, and a 9 oz. clear, plastic cup of water. Students will make a mark with the permanent marker on one piece of cloth and a mark with the Crayola marker on the other piece of cloth.

Ask:

  • What do you think will happen when you place each piece of cloth in the water? Why? Answers will vary.
  • Students will dip one of the pieces of cloth into the cup. Using their fingers, students will try to rub the mark out of the cloth.
  • Students will repeat with the other piece of cloth. Ask:
    • What happened to the ink in each piece of cloth? Students will find that they are able to get most, if not all, of the Crayola mark out, but very little of the permanent marker. The Crayola marker contains ink that is soluble in water.
    • Where did the ink go? The ink from the Crayola marker dissolved, or spread out into the water.
    • Why were you able to remove ink from one piece of cloth but not from the other? Answers will vary. Some inks dissolve more easily in water than others.

    Explore:

      • Explain that students will observe the effects of water on different markers more closely to help explain why one marker washed out and the other did not.
      • Give each group five coffee filters, and four different black markers to use along with the Crayola marker they already have. Allow students to replace water if needed. Give each student an Investigating Solubility Results page
      • Demonstrate how to fold a filter into fourths. Each group will fold all of their coffee filters into fourths. The students will use one of the markers to color a black dot near the folded corner of the filter. Use a pen or pencil to label the filter with the name of the marker. Repeat for all markers. Ask:
        • Do the marks look the same or different? Answers will vary.
        • What might be the reason that some look different, even though they are all black? Answers will vary.
        • What do you think will happen when the marks come in contact with water? Answers will vary.
      • Explain that students will contact each mark with the water to help observe the ink samples more closely. Demonstrate how to dip the very tip of the filter into the cup of water. The mark does not need to touch the water. Students will observe the water absorbing into the paper towel and then into the mark.
      •  

      • After testing each coffee filter, groups will place them on the paper towel. Students will observe the ink samples more closely using magnifying glasses or digital microscopes.
      • Students record results on the results page.

Explain:

  1. Groups will lay out their filters and walk around to compare their results with the other groups.
  2. Discuss and share the results. Ask:
  • How did each brand of marker react when the ink came in contact with water? None of the brands of markers contain the exact same colors.
  • What colors do you see? Colors may include blue, purple, red, yellow and green.
  • How many colors to do you see in each sample? Some samples may show only one or two colors, while others may show more.
  • Did the groups have similar results? Why or why not? Groups will experience similar colors, but the patterns will vary depending on the sizes of the marks and how the water absorbs into the filters.
  • What causes the black marker to separate into other colors? As the marker comes into contact with the water, the pigments that make up the black color dissolve into the filter. Some pigments continue to move with the water as it is absorbed by the filter, while others do not. This occurs because some pigments are more soluble, or dissolve better, and move quickly, while less water-soluble pigments move slowly.
  • Did all marks separate into colors? Students will notice that some marks dissolve very little into the coffee filter. This is because they were made with a permanent marker which is not water-soluble.
  • Why do you think the process of ink dissolving into the paper is called chromatography? Chromatography is a method used by scientists to separate the components of a mixture; chroma means color, and graph means to write.

Elaborate:

  1. Explain that students will work as forensic scientists and use chromatography to identify the type of marker used in writing a note.
  2. Assign each group one of the markers they tested. Record the marker assigned to each group on the board.
  3. Each group must write a note on a piece of copy paper. Collect the notes, and then pass them back out randomly to each group. Make sure that students do not receive the note they wrote.
  4. Groups will examine the notes they received and run a chromatography test to determine which of the markers was used to write the note. Students will compare the note with the tests they ran earlier.
  5. Students must conclude the marker and group that wrote their message and then share their results and conclusions with the class.
  6. Reveal which group wrote each note.

Evaluate:

  1. Refer back to the material that students rinsed in water at the beginning of the lesson. Ask:
    • Why were you able to clean off one mark but not the other? One mark was made by a water-soluble marker. The pigments were soluble in water and dissolved into the filter. The other mark was made by a permanent marker, so water could not remove it.
    • How might you remove the permanent marker? Using a soap or chemical may remove the marker.
  2. Complete the Water-soluble card match.
  3. Students record their reflections.

Resources:
Chromatography Detectives
http://web.missouri.edu/~hanuscind/4280/chromatography_learningcycle.pdf

Chem4Kids
http://www.chem4kids.com/file/matter_solution.html

___________________________
Girlstart is an award-winning Austin-based non-profit organization dedicated to empowering girls in science, technology, engineering, and math (STEM).

About Girlstart

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