Matter and Measurement

The information in this module corelates to Lecture 2. In this lecture we are covering:

1) The Scientific Method

2) Classifications of Matter

3) Basic Units of Measurement

Let's start with the Scientific Method.

The scientific method is used to produce systematically reliable results and conclusions when investigating any scientific topic. The investigation always starts with a simple question. How does this work?, why does this happen?, how much is produced?, Where does this go?, etc. Once you have established the question, you need to discover as much as possible about what is already known. This research is necessary to avoid redundant work and will help to form the parameters of the next step in the investigation - the hypothesis.

The hypothesis is a clearly stated summary of what "question" is being asked and what the expected outcome of the investigation will be. The hypothesis should be written so that is can be tested and it should be written as precisely as possible. A hypothesis can be positive or negative in its statement. For example, you may have heard the statement that eating Poprocks™ and Soda can cause your stomach to explode. This statement may or may not be an "urban legend". So if we were to ask a question, it would be "does the consumption of Poprocks™ and Soda cause the stomach to explode?" If we rephrase the question into a hypothesis, we might say in a positive manner that "The consumption of Poprocks™ and Soda will cause the stomach to explode" or in a negative manner, "The consumption of Poprocks™ and Soda will not cause the stomach to explode". Once we have established our hypothesis we then need to determine the experimental steps to take to determine the validity of our hypothesis.

Question: Does the consumption of Poprocks™ and Soda cause the stomach to explode?

Hypothesis: The consumption of Poprocks™ and Soda does not cause the stomach to explode.

Testing the Hypothesis

Possible ways to test the hypothesis:

Use mice or other animals and feed them Poprocks and soda and observe the results
Search for stories of people dying from the consumption of Poprocks and Soda in the primary literature
Create a simulated setting of the stomach and observe the results of adding the Poprocks to soda under controlled conditions.

Testing a hypothesis provides the most challenge to a researcher. The hypothesis we have just stated is that the consumption of Poprocks™ and Soda will not cause the stomach to explode. The question is how to test this hypothesis. I am pretty sure we can't just feed a group of people a lot of Poprocks and soda and wait to see if it kills them. That would be dangerous and unethical if our hypothesis is incorrect. The test we use needs to have "controls". Controls are rules that we impose on the tests so that the experiment will be reproducible. Controls can be as simple as comparing all data at the same temperature to as complicated as selecting subjects that have the same genetic background which of course would require intense preparatory testing. Deciding on a test for our hypothesis will be based on these controls as well as the time and often the money available to run the tests.

Analysis and Conclusions

Once all of the experimental data both qualitative and quantitative is collected, it must be processed and analyzed. Process of data could mean converting the data from one form to another. For instance you measured the mass and volume of the substance under study but you really need the density so you must calculate that value using the data you collected.

It could also mean simply collating a large amount of data. For instance if you interviewed 700 men regarding the sport(s) they watched over a weekend you would need to put the answers into a spreadsheet and "collect" the data so it can easily be read and patterns found.

Data collected: hours of sports watched by men in 48 hours

Once the data has been processed and analyzed, conclusions regarding the validity of the hypothesis are made. These answers to the question(s) that have been asked should be stated as either supporting or denying the basic hypothesis as it was stated.

In summary, here are the steps of the Scientific Method:

Scientific Method

Classifying Matter

We already defined chemistry: Chemistry is the branch of science that deals with the identification of the substances of which matter is composed; the investigation of their properties and the ways in which they interact, combine, and change; and the use of these processes to form new substances.

But in doing so we added several other terms, "substances", "matter", "properties", etc. that now need definitions of their own.

Matter is anything that has mass and volume i.e. takes up space. This pretty much means that chemistry is the study of just about everything. We define matter by its composition - what it is made of chemically. All matter is composed of elements. The periodic table shows that there are 118 known elements. The chart below contains a list of those elements. If you click on one of the elements you can find out about its properties and where it is found in nature.

The Phases of Matter

There are 4 accepted phases of matter (although some say there are now 5). Each is defined by its physical properties. The best way to describe the differences is in the densities or the energy levels of the phases:

Solid - Solids are substances that contain low energy molecules or atoms bound together very tightly creating a high density. They also have a defined shape.

Liquid - Liquids are made up of moderate energy molecules or atoms and are bound loosely together for a moderate density. Liquids have no defined shape but rather take on the shape of the container they are placed in.

Gas - Gases are made up of high energy molecules or atoms and are not bound together at all so their density and shape is dependent on the container in which they are placed.

Plasma - Plasmas are very high energy molecules that have a relatively high density as well. Plasmas are found in places like the sun and stars.

The Fifth state of matter is relatively new and man made. This state of matter is called a Bose-Einstein condensate. This state of matter was created by using lasers and magnets to supercool a gas until its atoms "clump" together creating something like a super cooled fluid. The cooling is very near absolute zero so the atoms or molecules are very low energy.

Phase Changes

The main phases we will explore are those that can be observed at normal temperatures and pressures. That is to say phases we might observe somewhere in the world without experimental manipulation. Solids, Liquids and gases. Phase Changes are the processes that occurs at the interface between the phases.

For a solid to change to a liquid we have to add heat and we call the process melting. For a solid to change to a gas, we have to lower the pressure significantly. This process is called sublimation.

For a liquid to change to a solid, we have to reduce the temperature and we are familiar with this process: Freezing. To change a liquid to a gas, we have to add heat and this is called vaporization. We commonly know the process as boiling but in science we are creating "vapors" so we call it vaporization.

Finally, to change a gas directly to a solid, we have to increase the pressure a LOT while maintaining the temperature and this process is called deposition. To change a gas to a liquid, we need to either increase the pressure or cool the temperature or both. This process is what makes it rain and is called condensation.

Phase Diagram of a substance showing the processes needed to move between phases.

You may have noticed a couple of points in the diagram above that we have not defined as yet: The Triple Point and the Critical Point.

The Triple Point is the Temperature and pressure at which all three phases of a substance exist together.

The Critical Point is the temperature and pressure at which the gas and liquid phase of the substance have the same density. This makes the two phases indistinguishable.

The interactive activities below will allow you to play through what happens at a molecular level when you change the temperature or pressure of a system:

Molecules and Mixtures

Units of Measurement

Units are very important in all sciences. Whenever you are expressing a number you have calculated or observed it is imperative that you report the unit in which the measurement was made as well. I always ask students how they would respond to the question, "Would you like a million?" and of course the immediate response is "a million what?" This is the purpose of units, they tell you the "what" part of the answer. And it is very important because if the unit in the question above is dollars that would be great but if the unit is blisters or something equally as painful that would be horrible. So ALWAYS input units with every number you express.

In chemistry as well as most other sciences we use SI units predominantly to express values. The International System of Units includes the metric system (system based on units in partitions of 10) as well as standard units called the SI base units for specific types of measurements. The table below shows the most common of these units and YOU SHOULD KNOW THEM!