8th Grade Lab Science (Cribb & Duane)
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MATTER IS "STUFF"

ALL MATTER HAS MASS & HAS VOLUME

 

OBJECTIVES:

bulletRecognize Characteristic Properties of Matter
bulletDistinguish mass from weight
bulletIdentify Unknown Substances By Measuring & Observing Characteristic Properties
bulletMeasure & Calculate Density of Matter

 

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PHYSICAL CHARACTERISTICS OF MATTER

Physical characteristics are properties that describe how the object looks, feels, tastes, etc.  They are descriptions of what it is.  Physical characteristics of matter include its mass, weight, volume, and density.  It also specifically describes its odor, shape, texture, and hardness.  In addition, physical properties describe whether the object is a solid, a liquid, or a gas – its phase of matter at room temperature.  These physical characteristics are described below:

 

Mass – Mass is a general property of matter that is the amount of matter it an object.  In other words, it is the amount of “stuff” there is.  It is easy to confuse the terms “mass” with “weight” but they are fundamentally different properties.  The mass of an object does not change from place to place.  You will measure mass using a triple beam balance and the units you will use are grams (g) and sometimes kilograms (kg).

 

Weight – Weight is not mass, but all objects have weight because they also have mass.  Boy does that sound confusing!  The distinction is important because weight is determined by gravity, while mass is not.

The weight of an object is determined by the force of the pull of gravity on the object.  Technically speaking, since gravity is a force, weight is a force. 

Because weight is based on the force of gravity, an object's weight may change from place to place.  If you weigh 120 lbs on Earth, your weight will be 20 lbs on the moon, since the Earth’s gravitational force is 6 times stronger than that of the moon.  You don’t need to diet, just change planets if you want to lose weight!  If your mass on earth is 60 kg however, you will still have a mass of 60 kg on the moon, so if you want to lose mass, cut out those fatty foods and try a little exercise!  To measure weight you need to use a spring scale.  You may know how many pounds (lb) you weigh, but the pound is not the standard unit for weight.  In science, the standard unit for weight is called the Newton (N).  

 

Volume – Volume describes how much space matter occupies.  It is not how much “stuff” there is, though that definition is a common mistake that students make.  The amount of space that an object takes up is the object’s volume.  It is a little tricky to measure the volume of gasses, but to measure the volume of a liquid, you will use a graduated cylinder for precise measurements, and a beaker or flask for less precise measurements.  The standard units that you will use are milliliters (mL), liters (L) and cubic centimeters (cm3or cc).  You will measure the volume of regular shaped objects using a metric ruler and calculating the length x width x height.  The volume of irregular shaped objects is measured using water displacement.

 

Density – Matter is anything that has mass and volume.  Scientists use those two properties to calculate the density of specific matter.  Density is the mass per unit volume of an object and it allows you to compare different types of matter.  Let me explain.  Which is “heavier” – lead or wood?  That is an ill-phrased question.  If you had a flake of lead from a pencil and a baseball bat made of wood, the wood would be heavier.  But if you had equal volumes of wood and lead, the lead would be heavier.  The proper way to phrase that question is – Which has a higher density – lead or wood?  To answer that you need to know the volume of the object in addition to the mass.  The density of a specific kind of matter is a property that helps identify it and distinguish it from all other kinds of matter.  Just ask Archimedes – the Greek philosopher of “Eureka” fame!  Since density is mass per unit volume you will need to measure both the mass and the volume of an object in order to calculate the density using the following formula:

 

Density = Mass / Volume

 

The standard unit for mass is grams (g) and the standard unit for volume is milliliters (mL).  So density is expressed as gram per milliliter (g / mL) or grams per cubic centimeter (g / cm3).  Scientists also compare the density of an object to the density of water, which is 1 g / mL.  This comparison is called specific gravity and is expressed as a ratio.

 

Table 5.1 Densities of some Materials

material density in g / cm3 material density in g / cm3
hydrogen 0.00009 aluminum 2.7
oxygen 0.0014 iron 7.9
water 1.0 gold 19.3

 

Solubility - Another physical property of a substance describes how well a substance dissolves in another substance.  Dissolving is a physical process.  If an object dissolves, that substance is soluble.  Solubility is a measure of how easily the substance dissolves in water.  You will measure the solubility of substances later this term.

 

PHASES OF MATTER

Physical properties – mass, volume density, odor, color, hardness etc, are properties that can be observed without changing the identity or essence of the substance.  Yet the same substance can have a different appearance.  Think of water, a substance that is fairly common, and that you as a living thing, cannot do without.  Ice, liquid water, and steam or water vapor all have a different appearance, but they are all the same substance.  As you know, a water molecule consists of hydrogen and oxygen.  That does not change whether water appears as solid ice, liquid water, or gaseous vapor.  These states are different phases.  The main phases of matter are solid, liquid, and gas, and matter can exist in any of these phases depending upon other factors.  What are those factors that determine the phase of matter in which a substance exists?  The primary ones that we will experiment with include temperature and pressure.  Phases of matter are technically “energy states of matter”.  Matter exists in a particular phase depending upon how fast the particles that make them up are moving and far apart they are from each other.

 

Solids – An ice cube, a pencil, a shaker of salt, and a metal coin are all solids.  They all share two important characteristics.  Solids have a definite shape and a definite volume.  The particles that make up a solid are packed tightly together and remain in a fixed position.  They vibrate back and forth in their fixed places.  This allows a solid to keep its shape since the particles cannot move from their places and flow around each other.  Solids that form a regular, repeating pattern with their particles are called crystals.

 

Liquids – Particles in a liquid are close together but they do not remain in a fixed position – they are free to move.  The particles of a liquid are moving much faster than those in a solid. As a result, they do not have a definite shape.  Instead, liquids take the shape of its container.  I liquid in a cube is square in shape, but the same liquid in a jar is round.  Although liquids do not have a definite shape, they do have a definite volume.  A 2 liter bottle of Coca Cola or Pepsi has the same volume if it is poured into a pitcher – same volume but different shape.  Even though particles in a liquid are always close to each other (always touching) they flow around each other.  Not all liquids flow as easily however – try pouring water and then honey to see the difference.  The measure of how easily a liquid flows is called viscosity.

 

Gases - Gases have neither a definite shape nor a definite volume.  A gas fills all the available space in the container, regardless of all the size or shape of the container.  This is because the particles in a gas are moving very rapidly and are spread apart.  There is a lot of empty space between these particles.  Some move as fast as 500 m / second!  These gas particles are constantly whizzing around and bumping into each other and the walls of the container – they may undergo 10 billion collisions each second!  The volume and temperature of gases depend upon the pressure.  The pressure of a gas is the measure of the number of collisions between particles.  The temperature of the gas also determines the pressure, as particles move faster as temperature rises.  Thus, there are more collision and a higher pressure.  We’ll focus more on the effects of temperature in this class.

 

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http://www.thetech.org/exhibits_events/noyce_center/topics/50a.html    TheTech from Weblearner: This site contains sites about the structure of matter, phases of matter, properties of matter, and compounds & mixtures.