A hypothesis is what you think the results of an investigation will be.
Cold Activated Thermochromic (CAT) Stickers will be used to explain how to write a hypothesis.
The hypothesis for many investigations is what the scientists hopes will happen. For example, Charles Goodyear spent much time and money trying to discover a formula for making natural rubber useful. While he changed his investigations, his hypothesis was basically the same in that the new mixture would be a type of rubber that would not be sticky. Read Charles Goodyear’s Story.
Hypothesis are not always formally written in a certain style. This is done when one is entering a contest called a science fair or if it is part of an assignment. Otherwise, a hypothesis can be a good guess.
A hypothesis should be based on some background knowledge, which can be from primary research or from secondary research.
Primary research is what you discover via investigations. Secondary research is what others have discovered and recorded. For more information about research, see Primary Research vs. Secondary Research.
CAT Sticker Research (Secondary)
CAT Stickers are made by coating white labels with a mixture of two colorants (anything that colors something else). One colorant is a thermochromic chemical in leuco dye and the other is pigment in acrylic paint. Water is added producing a liquid mixture that is painted on the labels. When the water evaporates the colorants adhere to the labels and do not rub or wash off.
Dyes with the characteristic of changing shape in response to a stimulus are called Leuco dyes. The shape of the dye molecules affect how the molecule absorbs the different colors making up white light (sunlight, indoor lighting). The molecular shape changes result in the dye changing from transparent to colored.
Thermochromic dyes change from colored to transparent when heated and back to their colored form when cooled. The leuco dyes on CAT Stickers have activation temperatures below room temperature. This means that the color of the leuco dye at room temperature changes when it is cooled to a certain temperature below room temperature. Acrylic paints do not change color with temperature fluctuations, thus a CAT sticker is the color of the acrylic paint when the leuco dye molecules are transparent. When the leuco dye molecules are colored, the CAT sticker color is a blend of the two colorants- the leuco dye and the paint.
CAT Sticker Investigation (Primary Research)
Purpose: Discover the temperature when the Leuco dye in CAT stickers is transparent and when it is colored?
Clues for investigating:
1. The leuco dye changes color at a temperature below room temperature. Thus, the stickers needs to be cooled. Try cooling with ice.
2. The acrylic paint doesn’t change color when cooled. Thus, when the leuco dye is transparent, the color of the acrylic paint will be seen.
3. The leuco dye color is never visible on the CAT Stickers. This is because when in its color form it blends with the color of the acrylic paint.
JVC CAT Sticker (Use Janice VanCleave CAT Stickers found at www.colorchangestickers.com)
small piece of ice (size should be easily held in you hand)
1. Observe and record the color of the JVC CAT Sticker at room temperature.
Example: The sticker’s entire surface is pink
2. Cool the pink colored JVC CAT Sticker with a piece of ice. Do this by rubbing the piece of ice over the surface of the sticker.
3. Observe and record the color of the sticker’s surface where it has been cooled.
Example: The cooled areas on the CAT sticker are purple
Analyze the Data (Results)
The CAT Mixture color is a combination of two colorants : dye and paint.
The possible combination are:
dye color + pink = purple [This is the best answer.]
dye color + purple = pink
Only two colors are visible, pink at room temperature and purple below room temperature. One of the colors, pink or purple, is produced by the blending of two colors. Purple cannot be mixed with another color to produce pink, but pink can be mixed with blue to make purple. While never visible, the thermochromic dye mixed with pink acrylic paint has a blue color.
Using room temperature as the standard, then thermochromic dyes that are transparent at room temperature and colored when cooled are called Cold Activated thermochromic dyes.
The color of CAT stickers at room temperature is the color of the acrylic paint. This is because the thermochromic dye is transparent at room temperature.
The color of the CAT stickers when cooled below room temperature is a blend of the color of the leuco dye and acrylic paint. This is because the thermochromic dye is colored at the cooler temperature.
Extended Science Questions
Generally, every experiment opens the door for more investigations. There are always more questions to investigate and answer.
In reference to the CAT Sticker in the previous investigation:
- What color is the leuco dye used in the CAT Mixture ? [My hypothesis would be blue. To test my hypothesis I would mix together any pink and blue paint.]
- What is the activation temperature of the Leuco dye used in the CAT Mixture? [My hypothesis would have to be a temperature range, such as below room temperature (?) and above the freezing temperature of water (0oC). I would have to design an investigation to measure the temperature at which the color of the sticker begins to change color. One way would be to dip the sticker into water at different temperatures from room temperature to (0oC).]
Science Cause/Effect Question
Hypothesis: Since mixing solutes with water affects the phase changing temperatures of water, then it is possible that mixing anything with the leuco dyes will affect the temperature at which the dye changes color.
Hypothesis: Since acrylic paint doesn’t change color with temperature changes, then mixing this paint with leuco dye will not affect the dye’s activation temperature.