More MCH Science Software

College Science Software BundleCollege Science Bundle: The three college level courses - General Chemistry, General Physics (calculus) and Organic chemistry, bundled together in one package.College Science Software Bundle

High School Science Bundle: The two high school level courses- Introductory Chemistry and General Physics (non- calculus), bundled together into one package. This bundle is very popular with High School and Home School students.Chemistry and Physics Software for High School and Home School

Stories in Higher-ed

Stories from Customers on how the Physical Chemistry textbook is being used around the world along with testimonials from users. We would love to hear how you have been using the book. Please feel free to leave your comment or contact us via the many options available onsite including Facebook and Twitter

Can you be Electrocuted while showering during an Electric Storm?

Lightning on the Columbia RiverIt is a known fact that water and electricity should not be used at the same time but have you ever wondered why? Were you ever told that you could be electrocuted while showering or bathing, during an electric storm? Can an electric current really flow through water? Continue reading

An Overview of Colligative Properties

Phase diagram of a solvent non-volatile solute system

Click to enlarge

The thermodynamics needed to treat the behaviour of solutions is explored in Chapter 5.8 of the Physical Chemistry book. The aim of this post is to use real life examples to explain the property of dilute solutions labelled colligative properties.

Colligative properties are an interesting scientific occurrence that can be applied in controlled environments (e.g. laboratory) as well as in day-to-day life.  Examples of colligative properties include freezing point, boiling point, vapour pressure and osmotic pressure.

What is a colligative property?

We can divide the properties of solutions into two main groups: colligative and non-colligative properties. A colligative property is a characteristic of a substance (such as its freezing point, boiling point, vapour pressure or osmotic pressure) that can be changed when a solute is added to it.

It is dependent only on the amount of dissolved particles in solution and it does not take into account their identity, structure or mass. In other words, irrespective of whether the substance is salt, sugar or gasoline – it will behave the same way.

Non-colligative properties on the other hand, depend on the identity of the dissolved species and the solvent.

Freezing Point Depression

It is common knowledge that salt applied dry is not efficient at melting ice in the winter until it is dissolved into brine. This process can be explained in terms of colligative properties. Once salt is dissolved in water, the solute (in this case salt brine) will determine its freeze-point lowering potential or freezing point depression.

Any substance that dissolves in water has this effect. In other words, adding another compound or substance to a liquid result in a phenomenon called freezing point depression, whereby the solution has a lower freezing point than that of the pure solvent. Similarly, this occurrence can be applied to explain why seawater has a lower freezing point than that of pure water.

Boiling Point Elevation

A common example of boiling point elevation can be observed when salt is added to water; thus increasing the boiling point of water. Boiling point elevation occurs when the boiling point of a solution becomes higher than the boiling point of a pure solvent. The temperature at which the solvent boils is increased by adding any non-volatile solute.

Vapour Pressure Lowering

Again we can explain vapour pressure lowering as a colligative property of matter because the vapour pressure of a liquid will decrease when another substance is dissolved in it. The decrease will be proportional to the quantity of the added substance.

We can analyse why this occurs. By adding substance to a liquid, the number of liquid molecules at the surface to escape and produce pressure will be fewer, since the surface now contains a mix of liquid and added substance. Therefore the solvent molecules will have a lower probability to escape the solution than the pure solvent. This fact is reflected in the lower vapour pressure for a solution relative to the pure solvent.

Osmotic Pressure

Measuring Osmotic Pressure

Osmotic pressure arises when there is a concentration difference between two solutions separated by a semi-permeable membrane. The (osmotic) pressure is the force of a liquid against this special membrane. The pressure required to stop osmosis is called the osmotic pressure (illustrated above in Figure 5.16).

For instance, when a cell is added to an aqueous solution with a much higher concentration of ions than the liquid within the cell, water leaves the cell by flowing through the cell membrane until the cell shrinks and ultimately breaks the membrane. Alternatively, when a cell is placed in a solution that has a much lower ionic strength, water pours into the cell, and the cell expands until the cell membrane bursts.

These are examples of colligative properties of matter which means that it depends on the number of particles in a solution (its concentration) and not on the structure of the particles or their mass. These properties ideally depend on changes in the entropy of the solution on dissolving the solute. The rationale for these colligative properties is the increase in entropy on mixing solutes with the water.

Phase Changes with the most amazing substance ever!

There is one substance today that still has the power to amaze and entertain me as it did as a child. I never lose a chance to sing its praises and or to expound on its powerful chemical characteristics to all my students, young and old alike. Continue reading

The world of Equilibrium

Screen Grab of interactive anim - Le Chatlier's principle from Physical Chemistry Book

Chemistry would be a whole lot simpler if all the reactions would just make their expected products (or even some by-products) and then be done. Reactants and products have a mind of their own though and are influenced by temperature, concentration, some even by the weather (pressure)! Worse, some products can’t seem to make up their mind and turn back into reactants. Continue reading

Digging into Phase Diagrams & Cooling Curves

Thermal Analysis

Thermal Analysis to determine a phase diagram (click to enlarge)

Condensed Binary Systems and  Thermal Analysis  are described in sections 6.4 and 6.5 of the Physical Chemistry textbook.

While most of us may not realise it, phase and phase transformations are ubiquitous in everyday life. The most simplistic illustration is a saucepan filled with boiling water – here the bubbles of steam formed by the water changes from liquid to vapour phase. Continue reading

Try our bestselling undergraduate Physical Chemistry courseware

Thermodynamics Module - Physical Chemistry
Thermodynamics module
Chapters 1 to 6 of Physical Chemistry - Laidler, Meiser, Sanctuary

Includes multimedia that opens on relevant pages and allows the student to visualize many of the concepts by varying parameters and plotting different graphs. Things students often have difficulty with, such as isothermal, isobaric, isochoric and adiabatic process, are clearly visualized.

Get it from: Thermodynamics Module - Physical Chemistry

Physical Chemistry - Laidler, Meiser, Sanctuary
Physical Chemistry textbook
by Laidler, Meiser, Sanctuary

This popular Physical Chemistry text book is now available in electronic format. We have preserved much of the material of the former hard copy editions, making changes to improve understanding of the concepts in addition to including some of the recent discoveries in physical chemistry. Many chapters have new sections and the coverage of several chapters has been greatly expanded.

Get it from: Physical Chemistry - Laidler, Meiser, Sanctuary

PChemistry Tips by Email

Don't miss out on Physical Chemistry tips & special offers sent via email

* indicates required


MCH on Twitter