Why do solutes dissolve better at higher temperatures, with stirring, and with larger surface area? Watch this video to learn how the particle model of matter explains solubility.
Lesson A6: The Particle Model and Mixtures
Figure A.2.6.1 – Hard water contains dissolved minerals.
Figure A.2.6.2 – Minerals in hard water deposit on surfaces over time, causing clogging.
Hard Water
When water flows over rocks or through the ground, mineral particles from rock dissolve in the water. Water containing a high concentration of dissolved minerals is called hard water. The tiny mineral particles in hard water include calcium, magnesium,
and iron.
Hard water creates some problems in homes. Hard water does not form a bubbly lather with soap. Instead, it combines with soap to leave soap scum on surfaces. When hard water evaporates, it leaves behind a layer of solid minerals, which is called scale.
Scale builds up quickly in machines that evaporate water, such as tea kettles and hot water heaters. Scale can also build up inside water pipes, which causes clogs.
Reading and Materials for This Lesson
Science in Action 8
Reading: Pages 32–37
Materials:
Sand, salt, gravel, vegetable oil, large jar, cups (plastic or glass), coffee filters, mesh strainer, funnel, spoon, eyedropper or turkey baster, water, cooking pot, stove.
Water Softeners
Figure A.2.6.3– Water softeners decrease the concentration of dissolved minerals in water.
Because hard water scale is difficult to clean and can clog pipes, people install water softeners in their homes. Water softeners are machines that remove minerals from hard water and change it to soft water. Soft water contains a low concentration
of dissolved minerals.
Water softeners contain a device called an ion exchanger. Ion exchangers contain a material called resin. Resin particles normally hold onto salt particles. Hard water is run through the resin. The resin releases its salt particles, because it has
a stronger desire to capture hard water mineral particles. Minerals are captured by the ion exchanger, which removes them from tap water.
Salt needs to be added to water softeners. Occasionally, salt needs to run through the ion exchanger resin, to wash out the hard water minerals and replenish the resin with salt particles.
Watch More
How Water Softeners Work
This video explains more about how water softeners work.
Connections
Figure A.2.6.4– Desalination plants use energy to separate saltwater into freshwater and solid salt.
Figure A.2.6.5– Desalination plants remove salt from ocean water using a process called reverse osmosis.
Figure A.2.6.6 – Reverse osmosis of salt water requires large amounts of energy.
Connection: Technology >> Drinkable Ocean Water
A growing concern around the world is the availability of fresh drinking water for growing populations. Fresh water is needed for human consumption and for growing food. Water shortages are particularly a concern in dry desert areas with high populations,
such as the Middle East, California, and North Africa.
Earth contains huge amounts of water. However, 97% of Earth’s water is located in the ocean. Ocean water contains dissolved salt. Saltwater is not drinkable. The human body gets rid of extra salt by eliminating water. If you drink saltwater, you actually
remove more water from your body than you take in, which leads to the health problem of dehydration. A similar issue happens with plants and saltwater.
One technology solution for freshwater shortages is desalination. Desalination is a process that removes salt from ocean water. To desalinate water, energy is used to pump seawater into pipes under high pressure. The pressure forces water through
very tiny holes in a filter. Salt can’t fit through these filter holes so it is separated from the solution.
Desalination is energy-intensive, which is its main drawback. A lot of electricity is needed to run the high pressure pumps. The high cost of electricity makes desalination very expensive. When that electricity is created by burning coal, it also
releases carbon dioxide emissions into the atmosphere, contributing to climate change.
Watch More
Desalination
This video talks about the problem of limited fresh water for all the world’s people and how to solve this problem through desalination.
This news report tours a desalination plant in San Diego, California. The benefits and disadvantages of desalination are explored in this video.
Think • Interpret • Decide
Dissolved Oxygen
This video shows an experiment measuring the amount of dissolved oxygen gas in water, as the temperature of the solution increases.
Questions:
After you have finished watching the video, carefully consider the following questions. Then, type or write your answers. When you have your answers, click the questions for feedback.
In general, higher temperatures cause more solute to dissolve in solvent. This experiment is opposite to the general rule. In this case, a higher temperature causes less solute to dissolve in the solvent. This experiment involved a gas solute
in a liquid solvent.
As the temperature of the solution increases, dissolved oxygen gas particles move faster in the solvent. This means the oxygen gas particles come into contact with the open surface of the solution more often. If oxygen gas particles touch the
surface of the solution, they can escape into the air. This process happens more frequently at higher temperatures, which is why as the temperature increases, the amount of dissolved oxygen gas in the solution decreases.
Figure A.2.6.7– Warm water is discharged from industrial plants back into waterways.
Figure A.2.6.8– Coal-fired power plants use water as a coolant.
Figure A.2.6.9– Thermal pollution causes algae to grow in waterways.
Thermal Pollution
Temperature generally increases the solubility of a solute in a solvent. The exception to this rule is the solubility of a gas solute in a liquid solvent. As the temperature increases, the solubility of a gas in a liquid actually decreases.
Industrial factories and power stations often use water to cool machinery. Thermal pollution occurs when the resulting warm water is discharged back into rivers or lakes. An increase in temperature decreases the amount of dissolved oxygen in waterways.
This is a problem, because fish and other organisms need oxygen to live. A decrease in dissolved oxygen disrupts water ecosystems. Over time, fish populations drop, and plant growth like algae rises.
Watch More
Dissolved Oxygen
Watch this video to learn more about dissolved oxygen in water.
Lesson Activity
Separating Mixtures
Problem:
Your task in this experiment is to design and test a procedure to separate a mixture of sand, salt, gravel, and oil.
Hypothesis:
A hypothesis is a testable
answer to a scientific question. In other words, what do you think the
result of this activity will be?
Hint: In this case, think about how you would state a prediction of how sand, salt, gravel, and oil might be separated.
Download:
DOWNLOAD this document. It provides a space for you to write your own
hypothesis. It also includes a sample hypothesis you can compare to your own. Also use the document to write your procedure and analysis questions that come later in this activity.
Materials:
Sand
Salt
Gravel
Vegetable oil
Large jar
Cups (plastic or glass)
Coffee filters
Mesh strainer
Funnel
Spoon
Eyedropper or turkey baster
Water
Cooking pot
Stove
Any other materials that are useful to complete the task
Safety Warning
You may choose to use a hot stove in this experiment. If so, it must be completed with the supervision and assistance of an adult. DO NOT attempt to use a stove by yourself.
Hot fluids and metal can burn you or others if you are not careful. Wear oven mitts when handling hot containers. Never leave a hot stove unattended. Take care when pouring hot fluids.
Instructions:
Design and write a procedure to completely separate a mixture of sand, salt, gravel, and oil. You can use any of the materials listed above, or additional materials as you wish. Your procedure should be written as numbered steps. The mixture components
need to be completely separated – so you can’t end up with oily rocks or sand!
Before you start writing your procedure, consider these questions:
Are there ways to physically separate or filter any of the mixture components?
Are there ways to separate any of the mixture components using solubility?
What substances in the mixture are soluble? In what solvents?
What substances in the mixture are insoluble? In what solvents?
Which substances would be easiest to separate first?
--------------------
Use the document you downloaded to write your procedure.
In a large jar, make a mixture of sand, salt, gravel, and oil. Put approximately ½ cup of each substance in the jar. Shake the mixture well.
Test your procedure. If you are not successful the first time, adjust your procedure and try again until you are successful at separating all four components.
Analysis Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
To separate oil from the mixture, you probably added water. Water particles and oil particles are insoluble because they are not attracted to each other. When water was added, all the oil eventually floated to the top of the container. The oil
could then be physically skimmed off the mixture with an eyedropper, turkey baster or spoon.
To separate gravel from the mixture, you probably poured the remaining water, salt, sand, and gravel through a mesh strainer. Sand and saltwater solution particles were small enough to fit through the strainer holes. Gravel particles are insoluble
in water, and chunks of gravel were too large to fit through the strainer holes, which separated them from everything else remaining in the mixture.
To separate sand from the mixture, you probably used a coffee filter and funnel. Salt and water particles were small enough to fit through the holes in the coffee filter paper. Sand particles are insoluble in water, and were too large to fit
through the coffee filter paper, which separated them from the saltwater solution.
When you added water to the mixture, the salt dissolved in water. Salt is soluble in water because salt and water particles are attracted to each other. This causes salt to spread out evenly throughout the solution. To separate salt from water,
you probably heated the saltwater solution. Heat caused water particles to evaporate from the solution, leaving behind salt particles in the bottom of the pot.
Sharing:
Congratulations on completing this activity! Consider sharing your completed work (or any thoughts and experiences you might have regarding this activity) in the course Sharing Forum.
You can also email your completed work to your teacher and ask for feedback.
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 6 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.
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.
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.
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.
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.
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.
Milk particles move faster at high temperatures compared to cold temperatures. When milk particles are moving more quickly, they are bump into hot chocolate particles more often. More frequent contact and attractions between milk particles and
hot chocolate particles causes the hot chocolate powder to dissolve faster.
Soda pop contains dissolved carbon dioxide gas. As the temperature of the soda pop increases, liquid and gas particles move around faster in the solution. As a result of faster motion, particles of carbon dioxide gas are in contact with the
solution’s surface more often. This causes carbon dioxide gas to escape from the pop to the atmosphere, making the pop go flat quickly.
Making hot brine ensures that all the vinegar and salt spread out evenly throughout the pickling solution. Rock salt has large grains, so if it was added directly to the pickle jars, it would take longer to dissolve. Making brine first ensures
that all cucumbers get exposed to equal amounts of salt and vinegar, which ensures that harmful bacteria don’t grow in the pickles.
An advantage of desalination is that once a desalination plant is built, it quickly provides freshwater to people and agriculture. This is especially helpful for people in dry climates. A disadvantage of desalination is that it requires lots
of energy to run, making it expensive and potentially harmful to the environment.
Epsom salt crystals have a large surface area. This means that only the outer salt particles on the crystal are exposed to bathwater particles, for dissolving. If the Epsom salts are not stirred in the bath, they take longer to bump into water
particles and completely dissolve.
Reading and Materials for This Lesson
