Lesson A3: Pure Substances and Mixtures

Key Ideas     Unit Checklist

  Video Lesson

Mixtures can take many forms. You can see the individual parts in some mixtures, while other mixtures look like a single substance. Watch the video below to learn about the differences between mixtures and pure substances.

 
 

  LessonA3: Pure Substances and Mixtures


Figure A.2.3.1 – Before 1950, the most popular way to drink pop was from a soda fountain.
Reading and Materials for This Lesson

Science in Action 8
Reading: Pages 18–23

Materials:
Tape (masking or cellophane), paper circular coffee filter or paper towel, water-soluble felt pens (different colours, like Crayola Original Markers™), tall cups, water, popsicle stick, empty and clean white plastic jug, (such as a milk jug or vinegar jug), sharp scissors, newspapers, 3 different coloured permanent markers (like Sharpie™), isopropyl alcohol (rubbing alcohol), eyedropper.


Figure A.2.3.2 – Before 1950, the most popular way to drink pop was from a soda fountain.
Where are those bubbles coming from?

Soft drinks are solutions of water, sugar, flavoured syrup, and carbon dioxide gas. Soft drinks are also called carbonated drinks, because they contain carbon dioxide.

People used to think that drinking carbonated water was healthy. Pharmacists in drugstores started selling carbonated water in the 1800’s. They started adding supposedly medicinal herbs to the fizzy water. For example, the bark and roots of the sassafras tree were added to carbonated water to make root beer. (Figure A.2.3.4)

While most soft drinks are bottled, soda fountains are still used in restaurants (Figure A.2.3.2). In soda fountains, carbon dioxide and cold water are pumped into a carbonating chamber. When the drink tap is pressed, carbonated water and flavoured syrup are released together into a glass.

Figure A.2.3.3 – Carbonated soft drinks are sweet and refreshing.
Figure A.2.3.4 – Root beer was once considered to be medicinal.

 Watch More

Soft Drinks

Watch this video to see how a factory produces bottled soft drinks.

 
 

Figure A.2.3.5 – Leaves contain many pigments that can be separated by chromatography.
Chromatography

Scientists use the method of chromatography to separate mixtures. In Greek, chroma means colour and graph means picture. About 100 years ago, chromatography was originally used to separate the different pigments in plant leaves, creating a “colour picture”.

Chromatography requires a carrier solvent and a test mixture. Different parts of the mixture travel at different speeds in the carrier solvent. As a result, some substances in the mixture travel further than others. The mixture separates and the parts become visible.

In science laboratories, special machines called chromatographs separate mixtures. Test solutions travel at different speeds through gas or liquid carrier solvents. Some uses of chromatography include analyzing pollutants dissolved in water, determining the components in a crude oil mixture, and testing athlete urine for illegal drugs.

Figure A.2.3.6 – Gas chromatograph machines are used to determine the components of mixtures.
Figure A.2.3.7– Chromatography is used to test pollutants in water or air.

  Try It!


Figure A.2.3.8 – Water soluble markers are necessary for this activity.
Pen Chromatography

Try this experiment to separate a mixture with chromatography.

  • Tape (masking or cellophane)
  • Paper circular coffee filter or paper towel
  • Different colours of water-soluble felt pens (Crayola Originals are best; look for markers described as being non-permanent, or water-based. NOTE: Permanent markers and dry-erase markers will not work in this activity.)
  • Tall cups
  • Water
  • Popsicle sticks

Take care with scissors; don't cut yourself or anyone else!
Instructions: 
    1. Cut the coffee filter or paper towel into several long strips.

    2. Attach one end of each coffee filter strip to a popsicle stick, using a small piece of tape.

    3. Use a water-soluble pen to draw a line along the bottom of one of the paper strips. Use a different coloured pen and draw a similar line on a different paper strip.

    4. Balance the popsicle stick on the top of the glass so that the strip hangs about â…” of the way to the bottom.

    5. Carefully add water to the glass so that the bottom of the strip touches the water, but the line on the paper remains dry.

    6. Allow the water to slowly soak into the paper and rise up through the felt pen line for about 15 minutes. What do you observe?


 
Questions: 

Think about the following question very carefully. Then, type or write your answer. After you have your answer, click the question for feedback.
 
Different coloured inks travelled at different speeds in the water as it slowly soaks along the paper. This allowed the different colours to separate from the ink mixture.

  Connections 

Figure A.2.3.9 – Ballpoint pen ink dries quickly.
Figure A.2.3.10 – People used to write with fountain pens dipped in ink.


Figure A.2.3.11 – There are many different types of inks and ink pens.
Connections – Technology
>> Communicating with Ink

Ink is an important technology, which has been essential to the development of many other technologies we enjoy. The development of ink allowed people to write and communicate their ideas to others. In the 1500’s, the invention of the ink printing press allowed people to print and share ideas faster, through books and newspapers. When people are able to share knowledge quickly, they can combine ideas to develop new technologies.

Some people think we don’t need ink anymore, because we have computers. However, ink pens are still very portable and do not rely on electricity to use. We also print a lot of documents using inkjet printers.

Ink is a colloid. It is made from tiny coloured pigment particles mixed in a solvent, to form a homogenous mixture. Different types of ink use different solvents. For example, ballpoint pens (Figure A.2.3.9) use an alcohol solvent that evaporates and dries quickly.  Fountain pens (Figure A.2.3.10) use water-based ink, which takes longer to dry. Gel pens (Figure A.2.3.11) contain a water-based gel.

 Watch More

What do you know about ink?

Ballpoint pens are easier to use, more portable, and less messy than fountain pens. Learn about the invention of ballpoint pens.

 
 
 
 
Many people in modern developed countries own an inkjet printer. Watch this video to learn more about how inkjet printers work.


 
 

  Try It! 

Marker Art

Try this experiment to blend inks together with a solvent. 

Materials: 
  • White plastic jug, empty and clean (such as a milk jug or vinegar jug)
  • Sharp scissors
  • Newspapers
  • Coloured permanent markers, at least 3 different colours (like
  • Sharpie™)
  • Isopropyl alcohol (rubbing alcohol)
  • Eyedropper

Take care with scissors; don’t cut yourself or anyone else!

This activity involves using isopropyl alcohol. This substance must be used with caution.

  • Do not directly inhale isopropyl alcohol fumes.
  • Isopropyl alcohol is very flammable; never use it anywhere near an open flame.
  • Isopropyl alcohol can cause skin and eye irritation; take care to not come in direct contact with it. If you do come in contact with it, flush with plenty of water.
  • Eye protection is recommended with handling isopropyl alcohol.
 Instructions:

  1. Cover a flat working surface with several layers of newspapers, to protect the surface from ink.

  2. Using the scissors, cut a shape out of the white plastic jug. The shape should be at least 10 cm wide.

  3. Scribble colour onto the plastic shape with the permanent markers. Try to use at least three different colours. You can scribble randomly or create patterns.

  4. Place the plastic shape flat onto the newspaper.

  5. With the eyedropper, place drops of isopropyl alcohol randomly on the coloured pen on the shape. Allow the colours to blend together.

  6. Observe the spots on the plastic that have not been touched by isopropyl alcohol. Add more drops to those spots.

  7. Allow the inks to dry.

  8. Now that you have experimented with permanent ink and solvents, you might want to try making some colourful bookmarks , or maybe some other interesting art:

 
 

Questions: 

Think about the following question very carefully. Then, type or write your answer. When you have your answer, click the question for feedback.

Permanent markers don’t dissolve in water, which is why they are “permanent” on many surfaces. However, as you saw, permanent markers do dissolve in isopropyl alcohol.

Cheesemaking

Cheese is made from cow, goat, or sheep milk. Milk is a colloid of fats and proteins in water. The first step of making cheese is to separate out the protein from the milk mixture. This is called curdling. Curdling happens naturally when milk goes bad, but there are different ways to deliberately curdle milk. Adding an acidic substance to milk will curdle it. A substance called rennet, from calves’ stomachs, also curdles milk.

To learn more about making cheese and other edible mixtures, click here to Explore with Elsie.


  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit A Lesson 3 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here .

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!

Be a Self-Check

Superhero!



Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

 
The purple ink in the pen was a mixture of red and blue inks. Water drops on the paper dissolved the purple ink. The red and blue inks travelled at different speeds in the water, which caused them to separate out of the purple ink.
Pop is a solution of water, sugar, flavour syrup, and carbon dioxide gas. The pop still tastes sweet because the sugar and flavour syrup is still dissolved in the pop. However, the carbon dioxide gas separated from the solution and escaped to the air. Carbon dioxide is no longer dissolved in the pop, which is why the pop is flat.
Eggs are an emulsifier in hollandaise sauce, to make the oily butter and water-based lemon juice mix together in a smooth colloid.
Permanent marker doesn’t dissolve in water, which is why water doesn’t remove the stain. However, permanent marker does dissolve in isopropyl alcohol, or rubbing alcohol. You could try applying some isopropyl alcohol to dissolve the stain.
Steel is made from iron, and is inexpensive. However, steel can rust. Putting a thin layer of rust-resistant metal on coins prevents rusting. The combination of a steel/copper structure and a rust-resistant coating creates inexpensive but durable coins.