CLASSIFICATION OF SUBSTANCES
Matter can be classified as either a mixture or a pure substance. Mixtures contain at least two substances. If you can see the different parts of the mixture it is called a mixture.E.g. Soil and concrete
Properties of mixtures depend on the proportions of the parts. Have you ever made a cup of coffee and added too much sugar? Pure substances have properties that are always the same. You can identify an unknown substance by testing its properties, e.g. Gold
Which of these substances is/ is not a mixture? What made it possible for you to determine whether or not it was a mechanical mixture? What about the other substances? Is it hard to tell them apart? Of course. It is hard to determine whether they are solutions or pure substances by just looking at them.
You must take into consideration all of their physical properties. Remember…Properties are characteristics that you can use to describe or identify different substances! Can you name three properties that would be useful or helpful in determining whether they are solutions or pure substances?
We can check whether the melting point, boiling point or density on the labels match the information in the table below. If they do match, we can say the substances are more than likely a pure substance. In your lab you will examine samples of unknown substances. While you examine these substances, you need to try and classify them as either a mixture, a solution or a pure substance.
Make sure you read and then write out the lab rules before you begin. Remember to follow the safety precautions of working in the lab and have all of your materials prepared before you start!
Lab Activity: Classifying Chemicals With Data Problem:
How can you classify unknown materials as mechanical mixtures, solutions or pure substances?
Hypothesis: How do you think it is going to turn out? Use the facts you already know to come up with a guess that might really make sense.
-12 samples of unknown materials
-data table about properties of pure substances (See below).
Compounds, element, periodic table, pure substance pure Substances
There are millions of kinds of pure substances. As scientists began studying substances, they found that there were certain simple substances that were in all of the materials that they studied.
They called these “building blocks of matter” elements. Elements are pure substances that cannot be broken down to any simpler substance. Compounds, are substances made up of two or more elements combined in specific proportions. If each letter in the alphabet is an element, then words would be compounds.
There are only about 100 elements in the universe that we know. Each of these elements has their own specific properties. Some are more common, some rare, some poisonous, some radioactive, and some explosive.
As scientists began studying substances, they found that there were certain simple substances that were in all of the materials that they studied. They called these “building blocks of matter” elements. Elements are pure substances that cannot be broken down to any simpler substance. Compounds, as we have seen, are substances made up of two or more elements combined in specific proportions.
Ex. Hydrogen + Oxygen = Water (H20)
Carbon + Hydrogen + Oxygen = Alcohol Elements, Compounds and the Atomic Theory
Atomic theory, atom, bonds, chemical formula, chemical symbol, compound, element, matter, mixture, molecule, particle theory, proportions
Elements, Compounds and the Atomic Theory
Atoms are the base of chemistry! They are the base for everything in the Universe! Matter is composed of atoms. The Particle Theory states that all matter is made of particles. The Atomic Theory goes farther to say that there is a difference between elements and compounds. Atoms are the smallest particles of elements. Since there are about 100 elements, there are about 100 kinds of atoms. Atoms can join together in many combinations to form molecules.
If the atoms of a molecule are the same, the substance is an element. If the atoms of a molecule are different, the substance is a compound. Classify each item as either an element (E), a compound (C), or a mixture (M). Use this site’s glossary for definitions of these terms.
You may also use the periodic table to help you identify elements.
- iron sulfide
- human body
- chop suey
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