1-4: Applications of Properties

Physical and chemical properties are used all the time in a variety of ways.

Density: "The Tip of the Iceberg"

There is a common saying which is used to talk about a situation in which only a small part of the total information is known. Or, it can be used if an event is the first of many similar events to come. We say that the small thing or event is "the tip of the iceberg."

The density of ice is less than that of water, so ice floats in water. We can also see this in a glass of ice-water:

The solid state of water (ice) has a lower density than the liquid state. As it turns out, this is a very unusual property: most substances have a higher density in the solid state than the liquid. For example, solid iron's density is about 7.9 g/cm³, but liquid iron's density is about 6.8 g/cm³ -- so, solid iron will sink in liquid iron, not float, because the solid is more dense.

Viscosity: Motor Oil

If you buy oil for a car's engine in a store, there will be a very important pair of numbers on the package.

Unless you know what you're looking for, you could miss these numbers:

The "5" and the "30" relate to the viscosity of the motor oil. The units are somewhat strange (square millimetres per second), but here's what the numbers mean:

1. When the oil is colder, that's the first number. When the engine first starts up, the oil will not flow as well, and the lower number represents this.

2. When the engine has been running for a while, the oil will be warmer, and that's the second number. Warmer oil flows more easily.

Each type of engine needs a different viscosity of oil. As it turns out, these numbers are the inverse of viscosity: a higher viscosity (resistance to flow) gives a lower number on motor oil. For example, 10W30 oil in comparison to 5W30 has a higher flow rate, and therefore lower viscosity, when it's cold.

Using the wrong type in an engine can damage it, so if you change the oil (or have someone else change it for you), look at the car's owners manual for that important information.

Hardness: Diamond Tipped Drill Bits

Diamond, a form of the element carbon, is best known for its use in jewelry.

When light enters diamond, it bends a lot. This causes the light to bounce off a lot of the inside surfaces of the diamond, making the light come out in a bunch of different places. We say the diamond "sparkles."

While diamonds have these interesting optical properties, their hardness makes them very useful when you want to cut through something else. You can buy drill bits to make holes in very hard materials such as ceramics, porcelain and steel, which have diamonds embedded in the end.

Eventually the diamonds will wear down and you have to replace the drill bit, but if the diamonds are not there at all, drilling through some materials would be impossible.

Reactivity with Oxygen: Stainless Steel

Steel is a mixture of iron and carbon, and has been used for thousands of years around the world. However, over time, the iron in steel can combine with oxygen in the air to create a compound known as iron oxide. We more commonly know this compound as rust.

One of the reasons steel is painted is to seal-off the steel from the oxygen in the air, to prevent rusting. If the paint gets scratched and oxygen can touch the steel, rusting will probably happen -- but this might take many years.

There are some objects which won't work well anymore if they rust, such as knives and forks. In the 1800s, scientists first noticed that if some of the element chromium is mixed in with iron, this alloy (a mixture of metals) would resist rusting and corrosion from different types of acid.

Early in the 1900s, stainless steel was advertised as the perfect material for flatware such as knives, forks and spoons. It is a part of our lives in so many ways, sometimes we don't even realize that stainless steel is everywhere. You probably have a lot of it in your kitchen drawers already!

Thermal conductivity: Aerogel

An aerogel is a very unique type of solid material; it is made from a gel (a high-viscosity liquid), but it is a solid.

It is an extremely low density solid, which is over 99% air by volume and is mostly see-through. It is made from silica, the same material from which glass is made, but obviously has some very different properties.

One very useful property, which NASA is interested in for a possible crewed mission to Mars, is its thermal conductivity: how good it is at transferring heat from one part of itself to another. Silica aerogels are extremely bad conductors of heat: they are excellent thermal insulators.

In the above picture, a blow torch is heating the bottom side of an aerogel which is about 1 cm thick. This flame is roughly 1000°C, but aerogel is so good at being a thermal insulator, it carries barely any of that heat through itself. The crayons on the top are made of wax, which will begin to melt at about 50°C... but so little heat is conducted through that they easily stay solid.

For a Mars mission, this article talks about how aerogel could be used as thermal insulation for a possible human colony there. While parts of Mars can reach comfortable Earth-like temperatures sometimes, the low density of the atmosphere means nighttime temperatures can go well below any temperature ever recorded on Earth.

Practice

The Basics

1. Solid aluminum has a density of 2.7 g/cm³. Liquid aluminum has a density of 2.4 g/cm³. Will a chunk of solid aluminum float in liquid aluminum, or will it sink? How do you know?

2. Sandpaper often has small pieces of silicon carbide glued to a thick piece of paper. When you sand a sharp corner off a piece of wood, what can you say about the hardness of silicon carbide, compared with the hardness of the wood?

Extensions

1. A chemical known as DDT was used to kill insects in the mid-20th century. It is soluble in fatty tissues, but is insoluble in water. Do some research to find out why this was a big problem for some animals, especially birds high up in food chains.