<meta http-equiv="refresh" content="1; url=/nojavascript/"> Laboratory Activities for Chapter 3 | CK-12 Foundation
Dismiss
Skip Navigation
You are reading an older version of this FlexBook® textbook: Chemistry - Second Edition Teacher's Edition (With Answers) Go to the latest version.

3.5: Laboratory Activities for Chapter 3

Created by: CK-12

The Scientific Method and the Socratic Method

The development of the scientific method was the result of centuries of cultural and societal evolution. Ranging from the philosophers of the Golden Age of Greece, through the applications of the Islamic scientists and into the ultimate flowering of the Scientific Revolution. The main premise of the scientific method is the synthesis of a hypothesis and the collection of evidence, and the persistent application of experimentation designed to support or disprove that hypothesis.

Among the first practitioners of what developed into the scientific method was Al Hazen (965 – 1039), an Islamic mathematician renowned for his extensive studies in the fields of optics, physics and psychology. In particular, Al Hazen may have been among the very first to collect experimental evidence and to assemble his observations. For example, he conducted a series of tests on observing the light of external lanterns from an inner room to lead to the conclusion that the light emanated from the lanterns, not from the long held idea that light instead was the result of particles emerging from the eyes.

An alternative approach, called the Socratic method, consists of a method of inquiry in some ways following a parallel approach to the scientific method. The dialogues of Socrates, as collected by his student, Plato, consisted of framing a question, often about a philosophical dilemma, and addressing this issue with a logical answer. The strategy was pursued with series of questions intended to support or undermine the problem at hand. The goal of the Socratic method was to arrive at a conclusion via this sequence, mainly by uncovering any inconsistencies in their logic. This type of reasoning, utilizing only logic and the “thought experiment,” lead to early misconceptions about the nature of physical realities. At times, the lack of simple experimentation produced erroneous conclusions that remained entrenched in many cultures for many years. The eminent philosopher Aristotle wrote about objects moving with “natural motion,” that is, moving according to their composition and their speed, a result of their weight. More than a thousand years elapsed before the experiments conducted by Galileo rolling different objects down a ramp removed the role of weight in free fall acceleration.

The Nature of Energy

The Four Fundamental Forces

There are four fundamental forces within all atoms, that dictate interactions between individual particles, and the large-scale behavior of all matter throughout the universe. They are the strong nuclear force, the weak nuclear force, the electromagnetic force, and the gravitational force.

Gravity is a force of attraction that acts between each and every particle in the universe. It is always attractive, never repulsive. It pulls matter together. It is gravity that keeps the planets in their orbits around the sun, the moon in its orbit around the earth, binds galaxies together in clusters, causes apples to fall from trees, and keeps you standing on the earth.

The electromagnetic force determines the ways in which electrically charged particles interact with each other and also with magnetic fields. This force can be attractive or repulsive. Like charges (two positive or two negative charges) repel each other; unlike charges attract. The electromagnetic force binds electrons in electron clouds around the positively charged nucleus of an atom and also governs the emission and absorption of light and other forms of electromagnetic radiation. Since the outside of atoms is an electron cloud, the electromagnetic force controls the interaction of materials when they touch each other and thus is the cause of the existence of liquids and solids and allows you to talk, move, breathe, and so on. All of the interactions between objects that you see every day is controlled by the electromagnetic force.

The strong nuclear force is the force that binds the atomic nucleus together. You may not have thought about it at the time the atomic nucleus was introduced to you but the atomic nucleus contains a number of positively charged protons held tightly together in a tiny space. From what we know about the repulsive force between like charges, the atomic nucleus should not stay together. The positive protons should repel each other strongly and fly apart. The fact that the protons and neutrons stay together in an atomic nucleus is because they are held there by an extremely strong force – namely, the strong nuclear force. Both the strong and weak nuclear forces operate only when the particles being attracted are extremely close together.

At this level, the weak nuclear force will skipped over with little consideration. We will just note that protons and neutrons are also composed of smaller particles (quarks, etc.) and these particles have a force which holds them together to form protons and neutrons. This force is the weak nuclear force.

Energy

Energy, like matter, is an important factor in our universe. Without energy, all matter – living and non-living – would be at a standstill; nothing would move, nothing would live. Energy is considered to be the “mover of matter”. The idea of energy is one that unites all the sciences. Energy does not have mass and does not take up space so it is not matter. Energy is defined as the ability to do work. An example of doing work (in the physics sense) is when you lift an object from the ground onto a table. The amount of work done depends on the force you had to apply to lift the object (its weight – or – the force of gravity on it) and the height you lifted the object. The greater the weight of the object or the higher it is lifted, the greater the amount of work done.

Energy comes in many forms. Besides mechanical energy, there is heat, light, sound, electricity, magnetism, chemical, and nuclear energy. Almost any form of energy can be converted into any other form. Our chief source of energy is the sun. It provides us with light, which can then be converted into other forms of energy. Light can be absorbed by matter and converted into heat. Light can also be absorbed by plants in the process of photosynthesis and be converted into chemical energy.

Kinetic and Potential Energy (Mechanical Energy)

Energy can be classified as either kinetic energy or potential energy. The original definition we gave for energy was the ability to do work. The ability to do work could also be stated as the “ability to make matter move”. Anything that can make a piece of matter move has energy. It should be obvious that a moving object has the ability to make another piece of matter move simply by colliding with it. Therefore, all moving objects have energy. This type of energy (the energy of moving objects) is called kinetic energy.

There are also non-moving objects that have the ability to make matter move. These objects have the ability to make matter move because of their position. For example, a rock held up in the air has the ability to make matter move – all that is required is that whatever is holding the rock up must release it. A stretched rubber band has the ability to make matter move – all that is required is that whatever is holding the rubber band must release it. This type of energy is stored energy or potential energy.

This baseball flying through the air has both kinetic and potential energy. The kinetic energy is due to its motion and the potential energy is due to the balls’ height above the ground.

The kinetic energy of an object can be calculated by multiplying one-half of its mass times its velocity squared.

KE = \frac{1}{2}mv^2

The gravitational potential energy of an object can be calculated by multiplying the mass of the object times the acceleration due to gravity times the height the object can fall.

PE = mgh

Potential energy is always present when two objects are attracted or repelled and are held in position. The most obvious case is an object that is held above the earth. The object is attracted to the earth by gravity but is kept from falling (gravitational potential energy). This same type of energy is present in bent sticks, compressed or stretched springs, stretched rubber bands, like or unlike electrical charges, and like or unlike magnetic poles. In all these cases, the potential energy can be calculated by multiplying the force of attraction (or repulsion) by the distance one object will move.

Energy Transmission

Scientists use three words to indicate the different methods by which energy moves from place to place. These three words are conduction, convection, and radiation.

Conduction

We are all familiar with the concept of molecules in constant random motion. This molecular motion increases when we heat the molecules and decreases when we cool the molecules. The energy of these moving molecules is kinetic energy. Kinetic energy is transferred between molecules when molecules at different temperatures collide with each other. When molecules at different temperatures collide with each other, energy is transferred from the “hotter” molecules to the “colder” molecules. Consider an object such as an iron bar – we can view the bar as a long chain of molecules crowded very close together. Remember that molecules or atoms in a solid are in a tightly packed pattern.

If this bar lies on a table for a few minutes, all the particles will be at about the same temperature. This is because each molecule is constantly bumping into its neighbors and these collisions transfer kinetic energy from a faster moving particle to a slower moving particle. If one end of this bar is placed into a flame and heated, the bar particles that are in the flame will get very hot.

When the hot particles bump into cold ones, the cold particles gain kinetic energy from the hot ones and thus the cold ones also become hot. Those particles then bump into their neighbors down the bar and eventually, all the molecules in the bar will be hot. This process of passing heat (kinetic energy) from particle to particle by collision is known as conduction.

Any time two objects at different temperatures touch each other, heat will be conducted from the hot one to the cold one by this process.

Molecules that make up living systems (like you) are called organic molecules. Most of these molecules are much more fragile than non-organic molecules. Non-organic molecules can usually reach quite a high temperature before the molecules are damaged. Organic molecules, however, are frequently long chains of carbon atoms and are easily to break if they are jerked around. If a hot object conducts heat to your hand, like all other conduction, the increased temperature causes the molecules of your hand to move around more rapidly. At temperatures at or below 40^ \circ C, your nervous system reacts in such a way that the sensation is not unpleasant. But at higher temperatures, your molecules begin moving around so rapidly that some of them break apart. When this happens, your nervous system sends a signal to your brain that you are in PAIN so that you will remove your hand from the heat as fast as possible. If many molecules are broken, the tissue is permanently damaged and must be replaced (healed) by the body.

Convection

Another way to move heat (energy) from one place to another is to heat up some substance, like air or water for example, and then to move the heated substance to another place. Essentially, the matter holds the energy in the form of heat, and when you move the matter to another place, you are also moving the energy it contains. In most homes, we use a furnace to heat air and use a fan to blow the hot air through ducts to various places in the house to warm it. In some places, water is heated and then pumped through pipes and into radiators to transport the heat from where it is produced to other areas. The process of moving matter that contains heat to other places is called convection.

Nature has its own convection system of heating up air in one place and then wind blows the air to another location. There are also convection currents in lakes and oceans, where cold water sinks and warm water rises causing water flow (and thus heat transfer) from place to place.

Radiation

When you build a campfire, the heat produced from the flames mostly goes upward. This is because hot air is less dense than cold air and so the hot air behaves like a helium balloon and goes straight up. If you stand a few feet to the side of a campfire, however, you will also feel heat coming from the fire. This heat does not get there by conduction or convection. This heat arrives at your position by radiation. Radiation is a type of energy transfer that can occur even through a vacuum – it needs no air or any other matter to carry it. This is quite different from conduction and convection which both require molecules of matter to transfer the energy.

This is the way that light from the sun travels through the vacuum of outer space and arrives at the earth. This type of energy is called electromagnetic radiation. There are various levels of energy for electromagnetic radiation. One of the lower energy forms of EMR are radio waves. As the energy of EMR increases, we encounter infra-red light, visible light, ultra-violet light, and x-rays. The highest energy form of EMR is gamma radiation. The radio and television signals we use for communication are electromagnetic radiation. Astronauts in outer space can still communicate with people on earth because the radio and TV signals do not need matter to travel through – they can travel through a vacuum.

Infra-red light is frequently used in remote control devices like your TV remote. The energy that cooks your food in a microwave oven is EMR. Radio signals are used to operate automatic garage door openers and infra-red “eyes” are used to stop the garage door if something is in the way of the door. Doctors and dentists use x-rays to make pictures of bones and teeth. X-rays are such a powerful form of EMR that the energy passes through skin, flesh, and many other substances. Electromagnetic radiation at the level of x-rays and gamma rays are so powerful that they can be dangerous to human beings.

Ultraviolet light is another form of EMR. UV light is the part of the sunlight responsible for tanning skin, burning skin, and in some cases, causing skin cancer.

For humans, the most common form of EMR is visible light, which our eyes use for vision.

A Little More on Gravity

Every particle of matter attracts every other particle of matter with a force which Isaac Newton named the force of gravity. We know this force exists, we can calculate the size and direction of the force, but we cannot yet explain how or why the force works. This force between particles of matter exists everywhere in the universe and it attracts all matter everywhere in the same way.

The size of the force of gravity is dependent on the masses of the two attracting objects and also on the distance between the centers of the two objects. The amount of matter in an object is called its mass and whenever the mass of one or both of the objects is increases, the force of gravity between the objects also increases. If the objects are brought closer together, the force of gravity increases and if the objects are moved farther apart, the force of gravity decreases.

The force of gravity between two small objects, such as two people, who are standing one meter apart is so small that we cannot even measure it. When one of the objects is very large, such as the earth, the force of gravity becomes large. The force of gravity pulling on a 50 \ kilogram person standing on the surface of the earth would be about 500 \ Newtons. In this English system, this force would correspond to about 110 \ pounds. The weight of a person is, in fact, the force of gravity acting on that person. If you weigh 120 \ pounds, it means that the earth is pulling on you with a force of 120 \ pounds.

If two objects the size of the earth were right next to each other, the force of gravity between them would be about 10,000,000,000,000,000,000,000,000 \ Newtons. As you can see, small objects have very small attractions to due gravity but very large objects can produce a gigantic force of gravity.

If we hold two 1,000,000 \ kg objects (like a battleship) one meter apart, the force of gravity between them would be about 70 \ Newtons. If we move the objects to a 10 \ meter separation, the force would become about 0.7 \ N and if we separate the objects by 100 \ meters, the force becomes 0.007 \ Newton. The force of gravity weakens rapidly as the distance between objects increases.

With two really large objects, like the earth and the sun, there is a certain distance where the force of gravity is just enough to keep the objects circling each other. The smaller object does most of the moving in this circle (actually, more like an oval).

Image Attributions

Description

Categories:

Grades:

Date Created:

Aug 18, 2012

Last Modified:

Jan 07, 2014
Files can only be attached to the latest version of None

Reviews

Please wait...
You need to be signed in to perform this action. Please sign-in and try again.
Please wait...
Image Detail
Sizes: Medium | Original
 
CK.SCI.ENG.TE.2.Chemistry.3.5

Original text