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Properties of Matter Most likely you have already been introduced, either in the lecture for this class or in a prior science class, to the various properties used to characterize matter. Chemical properties of matter only become apparent during a chemical reaction. On the other hand, a physical property is an aspect of a sample that can be observed without changing its chemical composition. Examples include properties such as color or texture. Further, physical properties can be further described as extensive properties, those that depend upon how much of the substance is present (Ex. mass or volume), or intensive properties, those that are independent of the amount (Ex. temperature or density) of substance present. One of the most common physical properties of matter is mass, also often referred to as weight. Although these two terms are often used interchangeably, they do not mean the same thing. Mass is used to describe the amount of matter that a substance contains, while weight is scientifically defined as the total gravitational force exerted on a substance. In fact, it is this notion that explains why astronauts are ‘weightless’ in space, yet retain their mass. Another physical property that will be investigated in this experiment is volume. Like mass, the volume of a substance is an extensive property as it also depends upon how much of the substance is present. Density What is interesting about density is that it provides a direct relationship between two extensive properties, mass and volume. The density of a substance is usually reported in metric units that are a combination of the normal units used for mass, i.e. grams (g) or kilograms (kg) and the normal units for volume, milliliters (mL), liters (L) or centimeters cubed (cm3). For example, the density of solids and liquids are generally reported in g/cm3 and g/mL, respectively, while for gases it is recorded as g/L. Density Calculations Density is calculated as the mass per unit volume of a substance.
The volume of a cylinder is given by the equation,
To complete the calculation of density for the cylinder we simply substitute the value of the mass and volume into equation 1: Seeing the resulting density of the metal cylinder, of which metal do you think it is composed? (Hint: read the introduction carefully) Exploring the Concept of Density through Experimentation In this particular experiment you will have two tasks: 1) to determine the identity of two unknown metal objects by matching their experimentally derived densities to a list of known metal densities and 2) to create a successful ‘submarine’ by matching the density of a mock submarine (made of a balloon and metal pellets) to the density of the salt water in a mock ocean. Identifying a Metal by its Density As you saw in the example above, once you have calculated the density of a metal object, that density can be used to identify the metal. As in the example, in order to experimentally determine the density of a metal object, you will need to measure two physical properties of that object: its mass and its volume. Mass is simple to obtain. You will simply weigh the cylinder on an analytical balance, described below. Obtaining the volume of your metal cylinders will require more work. Determining Volume To determine the volume of a liquid is easy; you simply place it in a graduated cylinder and record the resulting volume from the calibration on the side. In order to determine the volume of your metal objects, you will have to use one of two methods: volume by displacement or volume by calculation. The first method, volume by displacement, uses the displacement of water in a graduated cylinder to determine the volume of the metal object:
The volume of water that is displaced by the metal object is exactly equal to the volume of the metal object itself.
Reading a Graduated Cylinder Accurate measurement of this volume depends on the scientist's ability to correctly read the scale on the graduated cylinder. This reading is made more complicated by the formation of a meniscus caused by capillary action. Whenever liquids are held in a narrow container, the surface tension of the liquid causes a marked curvature of the upper surface. Specifically, this is referred to as a meniscus.
In the case of water, the meniscus is concave and in order to accurately record the volume, you have to observe where the center of the curve is located. At this point, it is appropriate to mention that in order to get the most accurate results you also have to incorporate some estimation. Volume by Calculation The second method you can use to obtain the volume of your metal objects is called volume by calculation. Depending on the shape of your metal object, there are several equations shown below that may be used to calculate its volume: For a cube V = s3, where s is the length of the side in cm. You should note that each of these volume equations will result in the unit of cm3. If your calculation does not result in this unit, you should check your calculations for errors.
The Vernier Caliper For each of the equations above you will need to measure the radius and/or the height (length) of your metal object. In order to measure these dimensions accurately, we will be using a device called a Vernier caliper. Fixed Scale in mm In order to use the instrument appropriately please note the following guidelines: 1) Place the metal object in the caliper to measure your dimension. 2) Close the caliper gently, but firmly, on the object so that the sides of the caliper are in firm contact with the object’s sides. 3) Find the “0” on the movable scale portion of the caliper. Looking just above and to the left of the “0” record, in millimeters (mm), the value of the non-movable scale. 4) Now find a line on the movable scale that completely coincides with a line on the non-movable scale. Record that value to the nearest tenth of a millimeter (mm).
Measuring Mass In addition to measuring the volume of your unknown metal object, in order to determine its density, you must also find its mass. There are many types of scales and balances, varying in range and accuracy, being used in today’s laboratories and commercial operations. Different balances exist for different purposes; i.e. you would not use a milligram balance to weigh out two tons of fertilizer. All of the balances in the laboratory use the same general technique to determine the mass of an object. What follows is a brief introduction to each of the different types of balances commonly used: 1. Double-pan Balance: objects of an accurately known mass are added to one side of a two-pan scale to ‘balance’ the object to be weighed until there is no difference between the two sides. 2. Mechanical Balance: similar to the double-pan balance, instead of placing weights on one side of the balance, internal weights inside the instrument are connected to dials on the front of the balance. 3. Electronic Balance: a magnetic field is used to observe the deflection—which is compared to stored data for known standards—of the pan when an object is placed on it. In a career as a scientist or engineer, all of these types of balances will be encountered. It would benefit you to become familiar with the ways in which each of them operates and to learn how to read the scales with the appropriate amount of precision and accuracy. Please read Appendix 1, Use of the Analytical Balance, found at the end of this laboratory manual prior to coming to class. Now that you have all of the information you need on the measurement and calculation of density, you are ready to begin... A Submarine Adventure Picture this…you are at war with a group of aliens; we will call them “Gatorians” for lack of a better term. They look like big lizards with green skin and orange eyes. Yuck! They have taken over your world and have isolated you and 19 others on an island somewhere in the South Pacific. But you have hope. If you can rendezvous with the military in Hawaii, you and your friends will be protected. Your only problem is how to get there. The “Gatorians” patrol the ocean surface continuously, and Hawaii is hundreds of miles from your position. Then someone in your group suggests that you build a submarine. That way you can avoid the “Gatorians” and still make it to Hawaii. You all decide that a submarine is the only way to go and then begin to design it. In order for the design to work, the submarine must float off the bottom of the ocean but not break the surface. This means that the density of the sub as a whole has to be very similar to the density of the water that surrounds the island. Real submarines use ballast systems, of course, but you have limited time and supplies so a design based on simple density is your only option (not to mention none of you are physicists and a workable ballast system is way out of your league). The group decides that they want you (the only scientist in the group) to design the sub and to make sure it will work. Before using what little resources you have to build the actual submarine, you devise the following experiment to test the idea first. Using 20 metal pellets to represent masses of the 20 people that have to travel inside the submarine and a balloon to represent the sub itself, you experimentally determine the density of the salt water and inflate the balloon to just the right volume so that the “submarine’s” density allows it to hover between the bottom of a pail of water and the surface. Your model system is quite a bit smaller than the sub will have to be, but if you can get the model to work then simply making the real sub 100 times bigger should also work as long as the density of the sub and the water remains the same. Matching the Density of a "Submarine" to the Density of the Water around It
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Or 
(Equation 1)
where r is the radius of the cylinder and h is the height or length of the cylinder. Remembering that the radius of a circle is half the diameter, the calculation of the volume of the cylinder is:
