Classification of Matter - Laboratory Activity

 

 

This activity uses a dichotomous key to help you classify the contents of 12 containers into the proper type of matter. The classification of matter is a fundamental step in physical science. You cannot directly observe all of the traits you will be looking for, therefore you must use your own knowledge and any other information you might have available. As you make each choice for the contents, write the number and letter of each statement you choose in the column labeled “justification”. Once you reach your final category, the statements you chose will be the justification for your choice.

 

 

Overview

A starting point for the scientific investigation of anything is to observe and find similarities and differences. Scientific work must be able to be understood and repeated by others studying the same thing in order to be useful. One way that scientists accomplish these goals is to classify things according to their traits. To help others to use their method of classification, they often construct a dichotomous key. A dichotomy is a division in two parts. In a dichotomous key there are a series of paired statements. If one is true about the item you wish to classify, you go on to another pair of statements. The alternative answer leads you to a different pair of statements. In this way, by choosing one or the other of paired statements, you are led to a final category for the object you are observing.

 

 

 

 

 

 

 

 

 

 

A Dichotomous Key to the Classification of Matter

1. A. The contents have mass and take up space.............................go to Q2.

B. The contents do not have mass or take up space- therefore it is ENERGY.

2. A. The contents have variable composition, a sample of this material is not uniform or different samples could differ in the proportions of the things that make it up......................................therefore it is a MIXTURE; go to Q3.

B. The contents have a definite composition. Every sample of this material will have the same composition...........therefore it is a PURE SUBSTANCE; go to Q6.

3. A. The contents are uniform throughout, although their proportions could differ from one sample to another.......therefore it is a HOMOGENOUS MIXTURE; go to Q5.

B. The contents of the vial vary in composition or traits from one part of the sample to another. They do not appear uniform or are known to vary from one part of a sample to another or to settle out over time................................. ......................therefore it is a HETEROGENOUS MIXTURE; go to Q4.

 

4. A. The contents may appear uniformly distributed, but solid particles will settle out of the liquid portion of the mixture -therefore it is a SUSPENSION.

B. The contents vary visibly in composition....................................................

................................... ....Therefore it is a HETEROGENOUS MIXTURE.

 

5. A. The particles of the homogenous mixture are atoms, ions or molecules, in a transparent mixture they will not scatter a beam of light...................................................................therefore it is a SOLUTION.

B. The particles of the homogenous mixture are larger than molecules, they make the mixture appear cloudy or milky and they scatter light in a transparent mixture..............................................therefore it is a COLLOID.

6. A. The substance is made up of a single type of atom that has a symbol and appears on the periodic table of the elements....therefore it is an ELEMENT.

B. The substance is made up of two or more atoms chemically combined in a fixed ratio......................................................therefore it is a COMPOUND.

Answer key to Classification of Matter:

After looking closely at each of the samples of substances and using the dichotomous key of classification, decide what each substance is and justify your answer by using the number of each statement that led you to the correct classification for the substance.

Sample and number

What type of matter is it?

Justification

1. gravel

 

 

2. sugar

 

 

3. Salt in Water

 

 

4. Sulfur

 

 

 

5. Lead

 

 

 

6. Beads

 

 

 

7. Milk of Magnesia

 

 

 

8. Sand

 

 

 

9. Copper

 

 

 

10. Water

 

 

 

11. Bromothymol Blue in Water

 

 

 

12. Glue