background: it s a matter of...

Background: It’s a Matter of Composition What is matter? Anything that occupies space and has mass is matter. All substances on Earth consist of matter, such as the air in our atmosphere, the water in the oceans, and the rocks that make up the Earth’s crust are all forms of matter in different physical states. Besides physical states, matter can also be classified according to composition. All matter on Earth can be classified as either pure substances or mixtures. Matter that consists of only one type of chemical is known as a pure substance. When two or more pure substances are mixed together they become a mixture.

C.4ABD: Physical and Chemical Changes and Properties Matter and the Periodic Table��

Sandy Beach

Copper Wire

Air We Breath

Let us examine some different forms of matter starting with the pure substances. The helium used for balloons is a gas made up of only helium atoms. Mercury, a liquid metal used in thermometers, and is a pure substance. A pure substance can be an element, but it can also be a compound. Carbon dioxide gas (CO2), distilled water (H2O), and limestone (calcium carbonate, CaCO3) are compounds that are pure substances. A compound is a pure substance if it can only be separated into its respective elements through chemical processes. When two or more pure substances are combined together they become a mixture. The air we breathe is a gaseous mixture made up of oxygen, nitrogen and various other inert gases. Seawater is a liquid mixture of several different dissolved salt compounds and water. Solid forms of matter can be mixtures, such as the sand and rocks on an ocean beach or alloys of metal such as brass, which is a mixture of copper and zinc. The difference between a pure substance and a mixture is that a mixture can be separated into different components by physical processes. There are three kinds of mixtures, heterogeneous mixtures, homogeneous mixtures (solutions) and colloids.

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•  What distinguishes a pure substance from a mixture? •  What is the difference between an extensive property and an intensive property?

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Background: It’s a Matter of Composition, continued For example, seawater is a homogeneous mixture, because the dissolved salts and the water cannot be distinguished from each other in the mixture. A liquid homogenous mixture is also known as a solution. A mixture of sand and water is heterogeneous, because the individual particles of sand can be seen as separate from the water. The heterogeneous mixture of sand and water is called a suspension, and if it is left standing, the sand will settle to the bottom and can be separated from the water by a physical process. Mixtures may be separated by a variety of physical means based on the substances physical properties. Those properties include melting and boiling points, density, and hardness. A heterogeneous mixture is a combination of two or more pure substances. This type of mixture does not have a uniform composition and has particles that are visibly distinguishable from each other. Sand and rocks mixed together is an example of a heterogeneous mixture. A heterogeneous mixture formed with a solid and a liquid in which the solid particles settle out upon standing is called a suspension. A mixture of sand and water is an example of a suspension. In a homogeneous mixture, also called a solution, the particles do not separate out when the mixture is allowed to stand. The composition of a homogeneous mixture is uniform, with no distinguishable particles. Air and salt water are examples of homogeneous mixtures.


Homogenous Liquid Heterogeneous Liquid Variety of Solids

Oil and Water = Mixture

Water (H2O) = Pure Substance

Variety of rocks = Mixture

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Background: It’s a Matter of Composition, continued While pure substances can not be separated by any means, either physical or chemical, mixtures may be separated by a variety of physical means based on the substance’s physical properties. Those properties include melting and boiling points, density, and hardness.


There is a state in between heterogeneous and homogeneous mixtures where the particles are not visibly distinguishable in the mixture and do not settle out when the mixture is allowed to stand, but the mixture is not homogeneous. Milk is a colloid made up of protein particles dissolved in a liquid. This third type of mixture is called a colloid. The composition of a colloid is uniform, however, when a light is shined through a transparent colloid, the particles can be seen by the reflection of the light and it forms a path of light in the mixture. This light test is called the Tyndall effect and is used to distinguish a homogeneous mixture from a colloid.

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Complete the Background Section of your Student Journal.

Part I: Plan Your Investigation Your Mission: Classify matter as pure substances or mixtures through investigation of extensive and intensive properties. Some physical properties, such as mass or volume, depend on the amount of a substance present. These are known as extensive properties. Other physical properties, such as density or boiling point, do not depend on the amount of a substance present. These are known as intensive properties. Develop a plan to separate pure substances from a heterogeneous mixture through investigation of the properties of the substances. Examine your mixture, identifying the different components that must be separated. Create a Question of Inquiry to help you focus on what you will be accomplishing during this investigation. Review the different techniques that may be used to separate substances. Identify what technique will work for what substance. What order will you perform the separation? What are some properties of each substance that might be helpful when deciding which separation technique to use? The salt will dissolve in water, but how much water do you need? How can the iron filings be separated from the sand? Some separation techniques are best performed with a dry mixture, so make sure to consider this when outlining your process. Be aware of how much liquid you are using to dissolve your substances substances, because you will eventually need to evaporate that liquid to recover the substances. Test your separation techniques with a small amount of your substances. Part II: Implement Your Investigation 1.  To isolate the mixture’s four different components, follow your separation

procedures. Try and avoid spills. 2.  After separation, determine the mass of each of your components. 3.  After recovering and weighing your components, your instructor will provide the

original masses of each of your components. Make sure to graph your data.



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Use Part I and II of your Student Journal to plan and implement your investigation.

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Separation Procedure 1.  Create a data chart. You will need 4 rows for the different substances and 4 columns,

one for the mass of the empty baggie or weigh boat, one for the combined mass of substance in baggie or boat, and one each for the recovered mass of the substance and initial mass of the substance in the mixture (provided by teacher)

2.  Label the three bags or boats as iron (Fe), salt (NaCl) and sand with the marker. The water will not be recovered and weighed

3.  Weigh 3 separate plastic bags (or use weighing boats). Record the mass of each one in the row for that component in the data table.

4.  Place the dry solid mixture on the top of a sheet of paper and use the magnet underneath the paper to separate out the iron filings. Repeat until all the iron has been removed.

5.  Place the recovered iron in the baggie or weigh boat labeled iron. 6.  Weigh the recovered iron in the weigh boat or baggie and record in the data table. 7.  Add enough water to cover the mixture and swirl it around to dissolve the salt. Pour

the water with the salt into another beaker. 8.  Use the hot plate with the evaporating dish to evaporate (or boil) the water with the

dissolved sodium chloride to recover the salt. 9.  Dry the sand in the beaker using the hot plate at the same time as the salt. The sand

may have to be left overnight to be weighed during the next class period. 10.  Scrape out the dried NaCl using the metal spatula and place it in the baggie or boat

labeled salt. 11.  Weigh the recovered NaCl in the weigh boat or baggie and record in the data table. 12.  Pour the dried sand into the baggie or boat labeled sand. 13.  Weigh the recovered sand (when dry) in the weigh boat or baggie and record in the

data table.

When finished, clean up lab area and put away all materials and equipment.

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