carbon dioxide (CO2) + water (H2O) + heat/light
or
In this lab you will light a candle and perform various tests to discover some things about burning and about candles. You will learn the practice of scientific observation. Observation is not the same as seeing. If five people see the same movie and then are each asked to tell about it you will hear five different stories. Some of the people are more observant than others or have better memories. You can make your memory better by carefully writing down your observations and you can become more observant by practicing.
When you complete your work on this lab you will be able to answer the following questions based on your observations:
You will be observing a candle and what happens when you light one. To understand what you are observing a little background would help. When you light a candle you initiate a type of chemical reaction called a combustion reaction. This reaction can be written in chemical shorthand as:
carbon dioxide (CO2) + water (H2O) + heat/light
CO2 +
H2O + heat/light
You can tell that a chemical reaction is occurring because of that heat and light: a sure sign. Combustion reactions require three things: fuel (hydrocarbons), oxygen, and a source of ignition. Hydrocarbons are molecules made up of hydrogen and carbon and are in fact what make up such things as gasoline, fuel oil and propane. Candles are made of hydrocarbon wax. Oxygen is supplied by the atmosphere and you supply the ignition (a match). One point of some importance is that different phases of matter burn at different rates. Solids burn more slowly than liquids and liquids burn more slowly than gases.
Combustion can be an imperfect process. That is, some of the hydrocarbons may not burn completely. When that happens several carbon-containing products can form besides carbon dioxide. First, carbon monoxide (a highly toxic gas) can form. This is only dangerous in cases of burning charcoal indoors or using a gas-powered generator in a closed space. Second, incomplete combustion can result in pure carbon: the hydrogen is burned away (it combines with oxygen to become water) and the carbon stays behind unburnt.
It may seem odd to think that burning the candle produces water but it is a fact even so. Water is a compound of hydrogen and oxygen and when those two elements combine the most common compound is H2O. It is hard to see the water that results from burning the candle because it is a gas (steam) and it is invisible.
A few words about carbon dioxide. It is a
gas that is more dense than air and so it can be collected from containers by
pouring. When CO2 is added to water
containing calcium hydroxide (Ca(OH)2) it reacts with the
Ca(OH)2 to form insoluble calcium
carbonate (CaCO3). This substance is
white and when the reaction occurs it makes the water turn cloudy. Water with
Ca(OH)2 dissolved in it is called
limewater.
In this lab you will make a series of observations. The purpose of doing so is to hone your observation skills for the labs you will do in the future and to learn something about an object you may have taken for granted.
Tie back loose hair and clothing. Before lighting a match don the safety goggles and keep them on during all activities performed while the candle is lit. Treat chemicals you don’t know anything about with as much caution as you treat bleach or gasoline. If you are not wearing shoes with closed toes and heels then you should be!
The procedure for this lab is mostly up to you. For each objective you must design and carry out experiments to answer the objective question(s). Keep the following in mind as you plan your work:
The lab is broken up into sections on the following pages. Complete each section and check in with your teacher to get his/her initials.
Write a formal lab report. Each individual student must write her/his own report. Attach your lab handout to your report.
You Analysis section must answer each of the questions in the Objectives section of the lab handout. In your answer to each question include:
Scientific explanations require that you refer to your observations as collected during class. Scientific information is best when it can be made quantitative: length, volume, time, etc. Report these data as part of your observations and use them to support your explanations.
You will be graded on the quality of your writing, the professionalism of your work’s appearance, the design and execution of your experiments and the degree of your understanding of the underlying science.
Record some quantitative observations about the candle before you light it. Record such things as length, mass, diameter, length of wick, or anything else that occurs to you. Try getting the mass of the candle at specific time intervals while burning: does its mass change over time?
Also record some qualitative observations about the candle before you light it. Record such things as wax color, color of wick, smell, new/old/damaged, or anything else that occurs to you.
Finally, record the sequence of events that occurs as you light the candle. Try to be as detailed as possible. These observations will be qualitative and should be as organized as possible. Reminder: each lab group member should write their own observations!
Record your data and observations in the space below.When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next objective. Initials will be given for recording a good set of observations about your candle.
Your teacher says that in order to undergo the chemical change called combustion, candles require oxygen. Oxygen is a gas that makes up about 20% of the Earth’s atmosphere (by volume). Can you prove that oxygen from the air is required for the candle to burn? Devise and carry out an experiment.
Write down the steps of your experiment below and show them to your teacher before proceeding.
When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next section. Initials will be given for a good experimental procedure.
Write down what you observe in your experiment, whether it seems relevant or not. Be sure that you have enough information to be able to answer the objective question.
When you have completed your work in this section check in with your teacher. This is a required part of the lab and your teacher’s initials are required before you can move on to the next section. Initials will be given for well-written observations and correct results.
Your teacher says that when hydrocarbon materials such as candle wax burns, they produce carbon dioxide (CO2). In the presence of CO2 limewater changes from clear to cloudy. (This is because insoluble particles of calcium carbonate—CaCO3—form in the water). Can you prove that candles do make CO2? Devise and carry out an experiment.
Write down the steps of your experiment below and show them to your teacher before proceeding.
Write down what you observe in your experiment, whether it seems relevant or not. Be sure that you have enough information to be able to answer the objective question.
Your teacher says that when hydrocarbon materials such as candle wax burns, they produce water (H2O). Burning (combustion) is a heat-releasing process and the chemical products are hot. If there is water present you will have to provide a way to cool it down in order to see it. Can you prove that candles do make H2O? Devise and carry out an experiment.
Write down the steps of your experiment below and show them to your teacher before proceeding.
Write down what you observe in your experiment, whether it seems relevant or not. Be sure that you have enough information to be able to answer the objective question.
Your teacher points out that there are at least three distinct regions in a candle flame. One: the blue-rimmed clear region very close to the wick. Two: the dim-orange-fading-to-bright-yellow region that produces light. Three: the clear region just above the visible flame. In the last several experiments you have investigated this third region, where the products of the combustion are found. Now take a moment to observe these other two flame regions. Devise and carry out an experiment to observe what is in these regions.
Write down the steps of your experiment below and show them to your teacher before proceeding.
Write down what you observe in your experiment, whether it seems relevant or not. Be sure that you have enough information to be able to answer the objective question.
Write a story about what happens to the solid wax as it melts, enters the flame, burns, and leaves the flame completely changed into CO2 and H2O.
Ask your teacher to do the Jumping Flame trick for you. Then answer the questions below.