Matter: Its Properties & Its Changes First Wild Card Tour

Tom DeRosa
and
Carolyn Reeves

Matter

Its Properties & Its Changes

By Tom DeRosa & Carolyn Reeves

Investigation #1: The Physical Side of Chemicals

Think about this. A detective collected samples of food from the table where a victim was eating when he collapsed. The detective sent them to a crime lab. A few days later, the lab called to say they had positively identified a poison in the victim’s food that was not in anyone else’s food. Have you ever wondered how someone in the crime lab could figure out what chemicals are present in food or in someone’s blood or in something else?

The Investigative Problems:

How can the physical properties of a chemical substance be used to help identify the substance?

Gather These Things:

Magnet
Iron nail
Sugar cube
Copper penny
Container of water
A piece of paraffin
Small amount of vegetable oil

Procedure & Observations

Your teacher will show you ten items. Your job is to identify one of the items on the basis of its physical properties. You should eliminate any item that doesn’t match the descriptions. These are the physical properties of the item: It is round. It is flat. You would not want to eat it. It would be hard to break. It is shiny. What is the item that has all of these properties?

Your teacher will give you some more substances to investigate, but each of these will be a pure chemical substance. They will be either an element or a compound.

Bring a magnet near each substance and observe if the magnet has an effect on it. Place each substance in a container of water and observe if it floats or sinks. Note if it is soluble (will dissolve) or insoluble (will not dissolve) in the water. Note also the color and whether it is shiny or dull. Put this information in a data table.

(sample of date table)

The Science Stuff

Physical properties are often characteristics you can see, hear, taste, smell, or feel, but may include any physical characteristics of a substance. You used some simple physical characteristics to identify one of the ten items you were first shown.

Some of the items you were shown were pure substances (like the glass), and some were a mixture of many substances (like the apple). A pure chemical substance could be either an element or a compound. (We’ll learn more about elements and compounds later.) A fragment of a pure substance would have the same properties as the whole substance. All of the basic particles in a pure substance are the same. For example, a piece of pure iron only contains particles of iron and a container of pure water only contains particles of water.

Properties such as size and shape were helpful in identifying the first items, but they are seldom considered in identifying pure chemical substances. The properties of the five pure substances listed in the chart will be present regardless of the size, shape, or amount of the substance. Scientists look for characteristics that will remain the same no matter where the chemical is found. Almost any substance can be made into a round shape, so this would not be helpful in knowing what chemical is present.

We examined physical properties of several pure substances, including the effects of a magnet, whether the substance would float or sink in water, whether the substance was soluble or insoluble in water, its color, and its shininess. There are many other properties we could have considered, such as odor, taste, density, hardness, brittleness, elasticity, melting and boiling temperatures, solubility in other liquids, conductivity of heat and electricity, and viscosity.

Making Connections

There is a huge need for methods, instruments, and trained people to identify chemical substances that are present in things. Identifying unknown chemicals is part of the study of analytical chemistry. This includes what chemical are present, their characteristics, and how much is present. There are many crime labs that hire people to help solve crimes by identifying things such as drugs, alcohol, poisons, or traces of gunpowder. Medical labs test blood and urine for the presence of many kinds of substances. Other labs help identify pollutants in the air, water, and environment. Industries must consistently monitor their products for impurities. These are only a few of the places where chemicals are analyzed.

One of the most important things any society can do is to maintain a clean source of water. During the Industrial Revolution, many factories were built next to a river so they could dump their wastes into the river. Congress eventually passed a number of laws to try and keep our water sources free of pollution. Even today, environmentalists look for better ways to prevent pesticides and other harmful chemicals from being washed into rivers and lakes after a rain.

Dig Deeper

Labs generally use both traditional methods and a variety of instruments to identify chemical substances. An instrument known as a spectroscope is often used to help analyze the chemicals in something. Do some reading about spectroscopes to find out how they work and what uses thy have.

Crime labs hire forensic scientists. What do forensic scientists do? Is there more than one kind of forensic scientist? If so, what are the different areas in which they work?

What are some of the U.S. laws that try to prevent water pollution? Do all countries have similar laws? Try to find the name of one charity whose mission is to provide clean water to people who don’t have clean water to drink.

What Did You Learn?

What are physical properties of chemical substances?
When scientists want to know what chemical substances are in an item, they seldom consider the size, shape, and amount of the item. Why is that?
Give ten examples of physical properties used by scientists to describe a chemical substance.
What is a pure chemical substance?
What are some of the things students learn about in analytical chemistry?
What are some of the main things that are don in medical labs?
How might an environmental agency use a lap that analyzes chemical substances?
Are the physical properties of pure iron the same anywhere pure iron is found?

copyright 2010, Cindy (Cindy’s Love Of Books)
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