Properties of Solutions
Reading
BJU: Ch. 12 "Solutions"
Topics
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes.
Here is a list of possible labs for this lesson. I will choose from this list when we get here.
BJU: Ch. 12 "Solutions"
Topics
- Types of solutions
- Solvents and solutes
- Molarity and percent concentration
- Colligative properties
Labs
Memo: 2020-2021 labs will include hands-on and virtual, and may vary as the Covid-19 situation changes.
Here is a list of possible labs for this lesson. I will choose from this list when we get here.
- The "Water Treatment lab - part II" is our regular lab, but there are numerous virtual labs which cover the topics well. There are also labs you can do at home. We'll decide when we get here.
- With proper supervision, you could do some or all of the Water Treatment lab at home.
- Famous solubility lab: Measure the solubility of NH4Cl aqueous solution over a wide range of temperatures. Plot solubility vs. temperature.
- There is also a well-known "colligative properties" lab using salt, alcohol, and celery to illustrate freezing point depression and osmosis.
- "Molarity" PhET weblab
- "Concentration" weblab
- "Salts and Solubility" PhET weblab
- "Sugar and Salt Solutions" PhET weblab
Study the video below: How water dissolves salt
Lecture overview
A solution is a homogenous mixture of two or more substances. The most abundant component is called the solvent, and the less abundant components are called solutes.
Solutions are very important in chemistry. Practically all of life (cells, tissues, blood) occurs in aqueous solution. Early chemists (Arrhenius, etc) devoted their life's work, and won Nobel Prizes, trying to figure out what solutions were and how they worked. Solutions play a big part in modern medical research, alternative (renewable) energy development, materials science, and many other areas.
Need-to-know
Solutions
Types of solutions
A solution is a homogenous mixture of two or more substances. The most abundant component is called the solvent, and the less abundant components are called solutes.
Solutions are very important in chemistry. Practically all of life (cells, tissues, blood) occurs in aqueous solution. Early chemists (Arrhenius, etc) devoted their life's work, and won Nobel Prizes, trying to figure out what solutions were and how they worked. Solutions play a big part in modern medical research, alternative (renewable) energy development, materials science, and many other areas.
Need-to-know
- Types of solutions: liquid, solid, and gaseous
- Concentration measurements: molarity, mass percent, and parts per million
- How temperature and pressure (and pH) effect solubility
- Boiling point elevation, freezing point depression, and osmotic pressure
- Colloidal dispersions
Solutions
- A solution is a homogeneous mixture comprised of two or more substances. In such a mixture, the "solute" is dissolved in the "solvent".
- The most abundant substance is called the solvent, and the other components are the solutes.
- An easy example is seawater.... a mixture of 3.5% salts (the solutes) dissolved in water (the solvent)
- A more subtle example is air.... a mixture of 22% oxygen and other gases (the solutes) dissolved in nitrogen gas (the solvent)
Types of solutions
- You can have solutions of solids, liquids, or gases
- Fourteen-karat gold is a "solution" of 42% silver (the solute) in 58% gold (the solvent)
- All the metal alloys - brass, bronze, copper-nickel, etc - can be thought of as solutions
- Oxygen dissolved in blood is a type of solution
Molarity concept
Parts per million
Colloids
- Molarity (M) is one way to measure the concentration of a solution. Molarity is defined as moles of solute per liter of solution (mols/L of solution). A 6M solution of HCl contains 6 moles of hydrogen chloride in 1 liter of aqueous solution. We would then refer to it as "1 liter of 6-molar hydrochloric acid". This is an important concept in chemistry and we'll cover it again and again.
Parts per million
- We often use "parts per million" or "ppm" to describe concentration, especially in aqueous solutions.
- 1 ppm = 1 mg/L
- For example, tap water in So. California contains about 500ppm dissolved solids. That means there are 500mg of various salts contained in 1L of tap water.
Colloids
- Colloidal dispersions are a very important class of mixtures
- The easiest way to imagine a colloidal mixture is to picture a beaker of water with fine silt stirred in. The silt particles aren't really "dissolved", but they are so small and light that they never settle to the bottom.
- Colloids aren't mixtures or suspensions. Mixtures are homogenous, and suspensions eventually settle out. Colloids aren't either.
- Examples: fog, clouds, mist, paint, smoke, blood, polluted water with fine particulate matter
Water Treatment Lab, part 2
"Environmental chemistry" makes a really good a launching pad for learning important concepts.
Removal of Calcium & Magnesium Hardness from water supplies using the Lime-Soda precipitation process. First, we will create 'ultra-hard' water by adding Calcium Sulfate, Calcium Chloride, and Calcium Carbonate salts to cause permanent and temporary (alkalinity-based) hardness. Solubility vs. pH charts will be consulted and these salts will be added up to their solubility limits. Soap-tests will be performed to compare soft-and-hard water's ability to generate suds. The sample will then be softened by precipitating-out the hardness and scale-causing compounds with Slaked Lime and Sodium Carbonate, using Alum as a flocculant aid. The dissolved hardness ions will form a thick precipitate and settle to the bottom, leaving softened water on top. Additional soap-testing will confirm the softness of the treated water. This process is used Worldwide to remove hardness and scale-causing contaminants from municipal and industrial feedwaters.
Handouts
"Environmental chemistry" makes a really good a launching pad for learning important concepts.
Removal of Calcium & Magnesium Hardness from water supplies using the Lime-Soda precipitation process. First, we will create 'ultra-hard' water by adding Calcium Sulfate, Calcium Chloride, and Calcium Carbonate salts to cause permanent and temporary (alkalinity-based) hardness. Solubility vs. pH charts will be consulted and these salts will be added up to their solubility limits. Soap-tests will be performed to compare soft-and-hard water's ability to generate suds. The sample will then be softened by precipitating-out the hardness and scale-causing compounds with Slaked Lime and Sodium Carbonate, using Alum as a flocculant aid. The dissolved hardness ions will form a thick precipitate and settle to the bottom, leaving softened water on top. Additional soap-testing will confirm the softness of the treated water. This process is used Worldwide to remove hardness and scale-causing contaminants from municipal and industrial feedwaters.
Handouts
| 11._solutions_handout_with_3_tables.docx |
| chart-_solubility_vs_temp_for_numerous_salts.jpg |
| chart-_solubility_vs_ph_for_6_heavy_metals__from_epa_.png |
Homework
NOTE: As of 3/4/2020 you can now turn in your completed assignments on Canvas.
NOTE: As of 3/4/2020 you can now turn in your completed assignments on Canvas.
| 11._gold_recover_assignment1.docx |
| 11._solutions_homework_problems.docx |